The White-striped Agaves: A Gallery of Desert Dazzle
As interest in cacti and succulents revs up worldwide and more desirable species and hybrids become available than ever before, a few plants continue to stand out despite more than a century in continued cultivation. Among them, the decoratively-marked and curly-threaded agave species from the deserts of Arizona and northern México still captivate growers with their attractive rosette forms and unusual but striking color patterns on their leaves.
(clicking on or hovering cursor over images here will display additional information and open them in an expanded lightbox)
The first species in horticulture from this somewhat artificial arrangement was introduced into cultivation in 1834. This was the central Mexican Agave filifera, described by the German botanist, Joseph Salm-Reifferscheid-Dyck. The diminutive Arizona-Sonoran boundary species, A. parviflora, was discovered and published in the 1850s but did not become popular in cultivation until almost a century later. A few other species entered cultivation later in the 19th century, most notably the closely-related and highly ornamental northeast Mexican A. victoriae-reginae (described by Moore in 1875) and A. nickelsiae (described by Roland-Gosselin in 1895). Other smaller species trickled into cultivation between the early 20th century (e.g. A. toumeyana), the 1970s (A. impressa) and the 1990s (A. microceps). Over the past decade, a couple additional taxa that are of interest to horticulture have been described from northwestern Mexico; A. pintilla (2011) from southeastern Durango and A. parviflora ssp. densiflora (2014) from southeastern Sonora. As botanical fieldwork continues in the dry forests and deserts of northern and westernn México, it is probable that other species or subspecies will be described from this group.
The agaves considered here are, with a few exceptions, exclusively Chihuahuan and Sonoran Desert plants ranging there from sea level (Agave felgeri) to over 8,400’/2,600 m (A. schidigera). The extralimital species are A. colimana (Colima and Michoacán), A. schidigera (from that same area south to western Guerrero) as well as A. filifera, occuring on the central Mexican plateau from Aguascalientes to México States at elevations from ~8,100’/2,500 m to over 10,000’/3,100 m. They are all members of the subgenus Littaea and include several sections; the Parviflorae, Marginatae and Filiferae (Gentry 1982). Largely as the result of their usually allopatric distributions, natural hybrids in this group are usually intersectional. Because of their concentration in arid environments at higher latitudes and elevations in Arizona and México they are, by and large, extraordinarily tough and cold hardy plants for ornamental desert succulents.
Stenciled leaf imprints are one of these agaves’ most compelling features, and many popular species show attractive patterns on the leaves that are embossed while budded in the growing point. “Look-downs” and closeup photographs of the rosette centers of most of the agaves shown here often reveal intricate, lacquered white geometric designs that are strongly reminiscent of certain types of tribal art. Likewise, copiously threaded or filiferous leaf margins on some species are also eye-catching and occur in many related Nearctic desert genera such as yuccas and hesperaloes, where they add a nice accent to these plants’ forms.
One of the obvious questions that arises when looking at these plants is why the convergent color patterns and rosette morphology across so many of the smaller, lightly-armed, mostly lithophytic agaves from the northern Sierra Madre Occidental and adjacent regions to the north and east? It seems reasonable to postulate that the bright white markings reflect sunlight and help reduce leaf surface heat, and that curled threads on the leaf margins function as catch-nets to augment the amount of surface area that plant has available to harvest dew and fog and direct this moisture to the rosette center. Both adaptations would be of obvious value to plants growing in very dry environments where sunshine is very bright almost year-round and rainfall is usually light and very seasonal. In fact, many of the “hairiest”-looking small agaves come the most arid parts of the Sonoran and Chihuahuan desert.
Beyond this, the zigzag patterns and curly leaf threads disrupt the silhouettes of the rosettes and are likely of camouflage value to the plants growing among rocks and grasses. With one exception, none of the species treated in this article possess the defensive marginal teeth that are otherwise ubiquitous in the genus Agave. Compared with the majority of their cogeners, most are effectively defenseless except for their terminal spines. These dark green and white striped designs are reminiscent of dazzle camouflage patterns that were widely applied to Allied ships during the First World War. While the advent of range finders and radar obviated the value of disruptive camo on maritime vessels and warships, there is little doubt that these patterns are very confusing to the eye. Dazzle patterns are also well known in many vertebrates (e.g. zebras and okapis, antshrikes, snowy and black and white owls, whiptail lizards, juvenile marine angelfish, etc.) to break up their outlines and to confuse potential predators and prey.
Despite a few species being highly sapogenous as part of their chemical arsenal (e.g. A. toumeyana and A. schottii), others mentioned here are known to be palatable to man after baking and have been used as sweet “wild treats” and for small-batch mezcal production by people in northwestern México. Rather surprisingly given their relatively small size, these include A. polianthiflora, A. parviflora and A. pintilla. Since we know that hoofed mammals sharing their range will browse on agave rosettes and inflorescences, and that the Pleistocene megafauna of this region was far more diverse than it is now, this disruptive color pattern of white striping on darker-colored leaves may have been of even more value to populations of these plants then than it is now. Extant native hoofed predators of agave leaves and stalks include Desert-Mexican bighorn sheep (Ovis canadensis nelsonii-”mexicana”), desert and Rocky Mountain mule deer (Odocoileus hemionus eremicus and O. h. hemionus), and collared peccary (Pecari tajacu). Besides these, other extinct indigenous ungulates that disappeared in the late Pleistocene also presumably browsed on many regional agaves.
The fact that this color pattern and habit model is almost entirely restricted to relatively small Agave species native to some of the driest areas of the eastern Sonoran and Chihuahuan Deserts, is absent from the Baja Californian Peninsula, and tends to become far less prevalent in the southern part of this complex’s range (Colima, Guerrero and México States) suggests that this adaptation evolved in response to very specific influences and/or exigencies of northern desert ecosystems.
Seed-grown plants from most species in this group usually lack conspicuous contrast striping until they reach a few years of age, which suggests that this color pattern comes at a cost to the plant. Agave victoriae-reginae is one notable exception to this rule. Other species will show light-colored leaf margins in lieu of striping until final subadult rosette form becomes evident. Conversely, offsets will usually be near duplicates of the mother plant from the start, possibly because their stripes add to the overall “visual noise” of both solitary adult plants and fairy rings.
Two species from this group are subject to special protections at both state and federal level in the U.S. and México. These species, Agave parviflora and A. victoriae-reginae, are also subject to restrictions on their international trade via their respective CITES Appendix I and II listings. While vendor lists show that wild seed continues to be collected from native populations of both species in Mexico, international commercial trade in these plants is now overwhelmingly based on artificially-propagated material. Unfortunately, local collection of A. victoriae-reginae and other species reportedly continues for the domestic market in México.
Mass production from both seed and plant tissue culture (PTC) has made young examples of the common forms of almost all of these white-striped agave species accessible to the budget of almost any succulent collector. Smaller and medium-sized examples of most of these species are readily available and retail at between USD 10.00-25.00 from internet and brick and mortar nurseries. Specimen-sized plants and coveted clones of the variegated forms can be considerably more expensive, with larger Agave nickelsiae, A. victoriae-reginae and A. impressa commanding USD 100.00-300.00 depending on the source. Large, well-grown variegated forms of these species can command much higher prices on eBay and at the high-end retail nurseries that carry them. During the height of the demand craze for A. victoriae-reginae ‘White Rhino’ in late 2017 and early 2018, I saw several larger, well-grown plants of this cultivar being sold for between USD 500.00 and USD 1,000.00.
On to the plants! Taxa and cultivars marked with an asterisk are currently being grown by the author in California:
Agave victoriae-reginae*. Queen Victoria Agave, lechuguilla. Two subspecies, victoriae-reginae* and ssp. swobodae. Undoubtedly, one of the most iconic of all ornamental succulent plants and a must-have for any agave collector. I have been growing different examples of this species continuously for almost 40 years both as pot plants and in the landscape and never tire of contemplating the perfect form and arresting leaf designs of a well-grown mature plant. This species, together with its two sibling species discussed below, have the most conspicuously-sculpted leaves in the genus. This trait, unlike the striping, is dominant in their hybrids where faint markings plus faceting on lower leaf surfaces usually betray its influence. There are a bewildering number of older varietal names published, reflecting the considerable intraspecific variability of this plant as well as the possible influence of past hybridization on the gene pool. Most are difficult to distinguish from one another (for me at least). The very best large forms can attain some size over the years and can reach ~30”/75 cm in diameter and several hundred leaves before finally bolting. Two subspecies are currently recognized, the nominate subspecies from eastern Nuevo León and extreme eastern Coahuila, and the similar ssp. swobodae (smaller at maturity, reportedly with lower leaf numbers) from southern Coahuila and eastern Durango. Both subspecies occur across a wide elevational range from the foothills around 1,900’/585 m to ~5,500’/1,700 m. I believe that a couple of the more distinct types in horticulture are valid when they have been stabilized and breed true from seed, most notably f. compacta (arguably, this is what ssp. swobodae represents). This form is generally more spherical in habit, with visibly higher leaf numbers than the standard form and with a strong tendency to offset in youth. That said, some plants labelled “f. compacta” in cultivation do “change their spots” and transform themselves into quite normal-looking vic-regs when planted out.
Two outstanding, fully mature examples of Agave victoriae-reginae f. compacta in cultivation. Left, Desert Botanical Garden, Phoenix, Arizona. Right, private garden, San Carlos, California.
Agave victoriae-reginae can usually be distinguished from the superficially-similar A. nickelsiae by their leaf surfaces and tip and terminal spine combinations. The former species has glossy leaf surfaces with white leaf margins and tips with short, fine gray or black straight or slightly curved terminal spines that erupt from a white base; A. nickelsiae has dusty-matte leaf surfaces, black leaf tips (sometimes with a narrow white band along the lower edge) with long and stout black, curved or S-shaped terminal spines, often flanked by two or more or less conspicuous secondary spines. For whatever reason, several of the yellow-variegated cultivars of A. victoriae-reginae display very formidable black terminal spines.
Left, leaf tip details of Agave victoriae-reginae and right, A. nickelsiae grown as fully-exposed potted plants in highland Guatemala. Author’s collection.
This is an incomparable species for use in focal and mass succulent plantings and I would strongly urge xeric gardeners with the conditions and space to establish at least one. Ganna Walska Lotusland in Montecito, California and some southern European collections were pioneers of the use of this species in this format (see Plate 48 in Irish’s “Agaves, Yuccas and Related Plants” 2000), but many other gardens – public and private – have followed suit. Its extreme cold and heat tolerance makes it an excellent subject for temperate and subtropical landscapes across the world, particularly if some overhead protection can be provided to minimize damage to the leaves from excess rain or hail. The Brits, French and Spaniards have grown some very nice-looking Agave victoriae-reginae outdoors in areas of mild climate in their countries. Very drought tolerant but always looks its best when provided with supplemental water during the dry months in desert environments. I have not seen it used in vertical plantings per se, but a few years back I experimented with planting them in rock crevices in a local landscape to great visual effect.
Left, a newly-established mass planting of Agave victoriae-reginae in a private garden on the Peninsula, San Francisco Bay Area, California. Author’s design. Right, an established mass planting at the Desert Botanical Garden, Phoenix Arizona. Both photos were taken in late 2016. The inter-planted cacti in the photo on the right have since been removed.
It is not a particularly good choice for lowland tropical gardens but can be grown under these conditions in pots filled with mineral-based substrates and protected from excess rain. The plants that I’ve looked at in Miami in the past, as well in as recent photos sent to me generally looked markedly inferior to those grown in the western states and carried unsightly skirts of dead, decomposing basal leaves.
Left, a pair of enormous (28”+/70 cm+ diameter) Agave victoriae-reginae ssp. victoriae-reginae on display at the Desert Botanical Gardens, Phoenix, Arizona. Right, an unusual A. victoriae-reginae clone showing vestigial marginal teeth, a rare occurrence that sometimes appears as a tiny percentage in some large batches of seed-grown plants. Plant at Ruth Bancroft Garden, Walnut Creek, California.
The two plants (both f. compacta) that I flowered in Guatemala did so following ~25 years from seed sow, but the larger forms reportedly take as long as 35-40 years to bolt in temperate climates.
Bare-rooted plants should be re-established in pots for about six months before planting out to the landscape. I have recently worked with several 22”/55 cm specimens sent clean bare-rooted from a nursery located outside of my area and suffered no setbacks nor leaf loss. From widespread reports this species is known to be very cold tolerant to 5-10 degrees F/-15 to -12 C if kept dry.
Although still widely believed to hybridize with Agave lechuguilla in nature, the parent in one well-known cross (= A. x pumila*) has now been corrected to A. nickelsiae by González-Elizondo, et. al. This same hybrid may also be the source of plants formerly called A. victoriae-reginae f. viridis in cultivation. Ruth Bancroft Garden and others grow an artificial cross apparently involving A. victoriae-reginae and A. lechuguilla (fide San Marcos Growers). The three live plants that I have seen all share stiff, narrow leaves, faint leaf markings, smooth leaf margins and long, stout terminal spines. There are reliable reports of hybrids involving A. victoriae-reginae and other agaves species that occur in sympatry growing in nature in the Huasteca Canyon and elsewhere in their range (W. Young, pers. comm.).
Two Agave victoriae-reginae hybrids in the landscape, both reportedly involving A. lechuguilla. Left, at the Ruth Bancroft Garden, Walnut Creek, California. Right, at Desert Foothills Nursery, Cave Creek, Arizona. I have a young example of another clone of this hybrid that shares most of the key features of these two plants, but with even more intimidating terminal spines.
Agave victoriae-reginae has many variegated sports, including several that have made their way into the broader market through PTC. These include ‘Kazo Bana’* and ‘Lemonade’* (aureo-marginate), ‘Kizan’* (cream aureo-marginate), ‘White Rhino’* (albo-marginate) and ‘Sun King’ (mediopicta-aurea). Some of the albovariegated clones can command very high prices when compared to normal-colored forms. The pair of unnamed mediopicta alba forms that I have seen may be the finest of all the variegated vic-regs. The clones with cream, tan and yellow variegated leaves will usually vary in color and degree of contrast depending on age, light intensity, nutrition and season. Albo-variegated forms are very color stable throughout their lives, but are particularly prone to etiolation or “stretching” if not grown with enough light.
Left, a young Agave victoriae-reginae ‘Lemonade’, right a subadult A. victoriae-reginae ‘White Rhino’. Author’s collection
Left, a young, offset-grown Agave victoriae-reginae ‘Kizan’ starting to show some contrast color on the lower leaf margins. Right, look-down on the rosette of an A. victoriae-reginae ‘White Rhino’. Author’s collection.
High-white clones of non-variegated plants may be priced at a slight premium from some sellers. Cultivar names are sometimes used for these dubiously distinct plants, such as Agave victoriae-reginae ‘Himesanoyuki’/‘Snow Princess’. A perusal of several flats of seedling A. victoriae-reginae from hand-pollination will usually yield at least a few heavily-marked individuals. Low-quality plants from PTC sometimes mutate, lose any semblance of apical dominance and clump themselves into oblivion over time.
Agave nickelsiae*. Ana Nickels’ Agave, King Ferdinand’s Agave, pintilla. Resurrected from synonymy with A. victoriae -reginae in 2011 by González-Elizondo, et. al., this very distinctive species was introduced to horticulture in the late 19th century by Ana Buck Nickels, owner of the Arcadia Nursery in Laredo, Texas. Originally published as A. nickelsii by Roland-Gosselin, the correct termination for a feminine appellation in botanical Latin (= -ae, -iae or -iana) has subsequently been appended. Better known under the synonym A. ferdinandi-regis Berger. A southern Coahuilan endemic occurring mostly between 4,900-5,500’/1,500 and 1,700 m. This is a fairly large and striking agave that can reach at least 36”/92 cm in diameter and over 28”/70 cm tall with time, although cultivated plants grown outside of central and southern Arizona and southern California are rarely seen with dimensions like some of those shown here.
It hybridizes promiscuously in nature with the at least two other sympatric agaves, including Agave asperrrima (formerly A. scabra) to produce plants that have been popular in cultivation for some time. Known variously as A. x pumila, A. x nigra, A. x saltilloensis, A. x nikelima, A. ‘Sharkskin’ or A. ‘Sharkskin Shoes’, these plants are instantly recognizable even when introgressed further. Since artificial hybrids are the product of several releases of seed-grown and offsetted material and have since been propagated via open pollination to F2, the formal clonal names ‘Sharkskin’, etc. that use single quotes, etc. are not valid for neither cultivated nor wild plants. Stable, pale-margined forms are in commercial cultivation from PTC (e.g. A. ‘Great White Shark’, A. ‘Mustard Shark’ and A. ‘Shark Bite’) but are still uncommon and high-priced.
Left, a nice colony of large Agave x Sharkskin at Ruth Bancroft Garden, Walnut Creek, California. Right, juvenile phase Agave x pumila. Author’s collection.
Of easy culture and usually a bit faster-growing than most forms of Agave victoriae-reginae. Very cold tolerant (to 5-10 degrees F/-15 to -12 C) but dislikes prolonged wets anywhere, but particularly in the winter.
Left, Agave nickelsiae in a private garden on the Peninsula in the San Francisco Bay Area. Right, a trio of 30”/75 cm diameter A. nickelsiae specimens for sale at a commercial nursery in Scottsdale, Arizona.
I have never flowered one, nor seen a cultivated plant that has flowered, so I suspect they take at least a few decades to bolt.
Curiously, while dozens of variegated sports of Agave victoriae-reginae have entered cultivation over the past 20 years, only a few conspicuously variegated A. nickelsiae have made it to market, at least two of which are mediopicta-aurea forms.
Agave pintilla*. Pintilla. A relatively new carve-out from A. victoriae-reginae by Dr. Socorro González-Elizondo and coauthors. This is a southeastern Durango endemic that is the only species in this complex that occurs on the Pacific versant, on the eastern slope of the Sierra Madre Occidental between ~4,700-5,200’/1,450 and 1,600 m. This is marginally the smallest species from the A. victoriae-reginae complex, with leaf numbers comparable to A. nickelsiae and long-triangular leaves. Mature rosettes reported to 24”/60 cm in diameter although are usually a bit smaller. Some individuals are among the most striking-looking agaves, with very broad, enamel white stripes on their glossy leaves. This species may have been introduced into ornamental horticulture some years back as an A. victoriae-reginae or A. nickelsiae wild-collected seed release, since there are larger in cultivation in the US that match the description and images of wild A. pintilla. Recent introduction of A. pintilla plantlets grown from seed collected in habitat show they have fairly long, glossy leaves, are noticeably darker in color, have scattered striations and are markedly more tuberculate on the undersides of their narrow-triangular leaves as young plants than most A. nickelsiae I have handled. All have elongated, stout terminal spines like A. nickelsiae but the leaf tips are white as in A. victoriae-reginae. After five years’ growth and at 7-10”/17-25 cm diameter, mine are just beginning to show first evidence of the very vivid white striping that this species is best known for. Limited trials and its origins suggest that it probably as weather tolerant as its close relatives. Due to its size and rarity in cultivation, coupled with its slow growth, A. pintilla is probably best suited as a pot plant for most collectors until it gets some size to it. Presumably cold hardy to 10-15 F/-12 to -9.5 C.
Known to hybridize in nature with Agave salmiana ssp. crassispina to produce a very robust-looking, concolorous plant.
Fieldwork over the past decade by Mexican and U.S. researchers has been invaluable in clarifying the status of all the populations in the Agave victoriae-reginae complex. It has also been useful to partially sort out the confusion left behind by Howard Scott Gentry – who gave surprisingly short shrift to these plants in his 1982 monograph - and other older taxonomists and authors. It is particularly interesting to note that the different taxa proposed by González-Elizondo, et. al. are shown mapped as disjunct, allopatric populations that, in a couple cases, occur quite distant from one another. Their detailed analysis of the natural hybrid swarms interbreeding with each other/back to the different species in nature is also very interesting and helps to shed light on the probable origins of some problematic plants in cultivation (e.g. A. victoriae-reginae f. viridis = A. nickelsiae x lechuguilla/A. x pumila). Further research into the incidence and distribution of wild hybridization within this species group is needed.
Agave impressa*. Masparillo. If it weren’t for its formidable mature size, sharp marginal teeth and reasonably fast growth, A. impressa would be an extremely popular pot plant with succulent enthusiasts. This very beautiful species from low elevations of the western foothills of the Sierra Madre Occidental in Sinaloa and Nayarit gets BIG in cultivation, readily topping 5’/1.60 m in diameter. While not as cold sensitive as its tropical origins suggest, it will reliably blow up when kept frigid and wet – or just very, very cold - in winter. Gentry (1982) mentioned that his experience with small wild-collected plants taken to collections in southern Florida and southern California was that the species presented “difficulties” in cultivation. Fortunately, this has not been the recent case with seed-grown and PTC origin plants in California. Large plants that I have grown under old-growth oak canopy in the landscape in northern California have survived overnight lows of 26 degrees F/-3.3 C with frost blankets and shown surprisingly little damage. Wet winters will produce some rotten basal leaves and leaf tips, despite excellent drainage and preventive drenches of Banrot (= etridiazole and thiophanate-methyl), but damage is usually more or less grown through by the late spring. Unprotected plants exposed to temperatures below freezing for prolonged periods will die quickly. Plants available from both seed-grown introductions and PTC, including the “Green Giant” clone sold by Rancho Soledad Nurseries and others. A fantastic plant for succulent gardens with some overhead shelter or fortunate enough to experience dry, fairly mild winters. Non-offsetting so far. Seedling plants show little evidence of leaf imprinting until over 10”/25 cm in diameter. Some seed-grown plants from southern Sinaloan accessions have pale pink striping in youth.
Agave parviflora*. Small-flowered agave, Santa Cruz striped agave, sobari. Three currently accepted subspecies, ssp. parviflora*, ssp. flexiflora* and ssp. densiflora*. The nominate subspecies is one of the smallest agaves (6-10”/15-25 cm diameter), is fairly localized and threatened with extinction in parts of its native range in the mountains of extreme south-central Arizona and northwestern Sonora. The other two (?) subspecies are also restricted to small populations in the grasslands and oak woodlands in northwestern Sonora (ssp. flexiflora) and southeastern Sonora (ssp. densiflora). Gentry (1972) segregated plants with deflexed corollas as ssp. flexiflora. Some plants exhibiting this trait also have longer, more linear leaves than the nominate subspecies, and cultivated plants under this name usually match this description together with having lightly-marked upper leaf surfaces. Since this peculiar flower morphology is reported to occur in and adjacent to populations recognized as ssp. parviflora, it may be that this is just a local variant. Single plants in cultivation are genuine dwarf agaves and can easily be grown to flowering size in 6”/15 cm pots, although ssp. densiflora is almost twice the size of the nominate form and will require more legroom when mature. Many A. parviflora show a leaf morphology that unusual in agaves in that the widest areas of the leaf are located at basal AND apical ends. My somewhat limited experience with these plants confirms others’ views that they can be relatively fast-growing in cultivation and that some clones offset reliably while others don’t. They do appear to resent bare-root transplanting, so care should be taken when re-establishing material purchased online from out of state nurseries, particularly if they are dehydrated on arrival. Cold tolerant to 10-15 degrees F/-12 to -9.5 C.
Agave parviflora can be extremely variable as to the amount of white and number of marginal threads that the leaves show on individual plants. Some very good clones are very heavily marked, look almost white and are very bristly. It also has a few variegated forms in PTC, including the very attractive clone ‘Pinpoint’ – a mediopicta alba form.
Agave polianthiflora*. Red-flowered agave. Mescalito. Essentially indistinguishable from A. parviflora when not in flower. Usually about the same size at maturity as a large example of the nominate subspecies of A. parviflora (8-12”/20-30 cm). May occur at higher elevations (to 6,500’/2,000 m) than A. parviflora but does occurs sympatrically with ssp. densiflora near Yecora, Sonora state at 4,500-5,200’/1,400-1,600 m. Reportedly still common in nature. Overall, a very handsome plant in flower with orange, rose or red peduncles and flowers. Its care is the same as for A. parviflora and A. toumeyana. Very cold tolerant to 5-10 degrees F/-15 to -12 C when kept dry.
Agave toumeyana*. Toumey’s agave. Two subspecies, ssp. toumeyana* and ssp. bella*. A very beautiful, compact and frondose species in nature that rarely looks anywhere near as good in cultivation. A central Arizona endemic usually found growing as a lithophyte or in rocky scrub at higher elevations but may also occur lower at ~2000-2,500’/615-770 m. Very cold tolerant if kept dry, but often briefly buried by snow in winter at higher elevations in habitat. Not especially tolerant of prolonged cold, wet winter conditions. Subspecies are differentiated by leaf size as adults and by the presence (ssp. bella) or absence (ssp. toumeyana) of denticles or tiny spines visible along the basal edges of their leaves. Some of best ecotypes of ssp. bella are very small (~6”/15 diameter) and have very wide, bright white striping on their leaves. These forms are among the smallest and showiest of the tabletop agaves. Unless mass planted in a suitable environment, probably wasted in most landscapes. Like its close relatives A. parviflora and A. polianthiflora, “hard” pot cultivation (full morning and early afternoon sunshine, mineral substrates, spare watering, light fertilization) is required to develop and maintain a natural appearance. Like others in captivity, mine get insufficient light and too much water to closely resemble the small, tight rosettes of wild plants. Cold tolerant to at least 10-15 degrees F/-12 to -9.5 C.
The natural hybrid. At a few upland localities in central Arizona, Agave toumeyana ssp. bella hybridizes with the sympatric A. chrysantha to produce A. x arizonica*. This taxon was discovered in the 1960s, described as a full species and placed in Section Urceolatae (alongside A. utahensis*) by Gentry and Weber in 1970. As such, it was considered to be critically threatened with extinction and vulnerable to commercial collecting pressure. It was subsequently listed as both an Endangered Species by the US Fish and Wildlife Service in 1984 and on CITES Appendix I in 1987. Ironically, prior to being added to to CITES, the US Forestry Service had petitioned that it be de-listed from the ESA in 1985, based on its (then) suspected F1 hybrid origin. It was removed from the Federal List of Endangered and Threatened Plants in 2006 and from CITES in 2007. It is still considered to be a threatened natural hybrid in Arizona and receives limited protection from wild collection at state level. This is a small (14-16”/35-40 cm diameter x 12-14”/30-35 cm tall), cold tolerant agave (to 15-20 F/-9.5 to -6.7 C) that grows well as both a pot plant and in the landscape. It tends to offset prolifically when young, so judicious pup removal will produce a more attractive-looking specimen. When it bolts, stand back since this hybrid is famous for its outsized ~12’/3.70 m tall inflorescences. This plant was undoubtedly more in demand by specialist collectors when it was still considered to be a critically endangered species. While not particularly common in cultivation outside of succulent collections in Arizona and southern California, it has been further hybridized in open-pollinated events to produce small, attractive F2 pot plants such as A. ‘Dianita’.
Left, a young group of Agave x arizonica. Author’s collection. Right, a group of the F2 hybrid that has A. x arizonica as the seed parent, A. x ‘Dianita’ at the Desert Botanical Garden, Phoenix, Arizona.
Agave schottii. Shin digger. Amole. Two subspecies (for now), ssp. schottii and ssp. treleasii. Gentry (1982) states, “The plants have little if any value as ornamentals”. OK, this is the obnoxious small maguey that no one wants to grow, but it still fits in here as an untidy, homely sibling. Part of Section Parviflorae, its closest relative are the three species mentioned just previously. Endemic to south central and southern Arizona, the Animas region in extreme southwestern New Mexico, northern Sonora and northwestern Chihuahua. Prefers open grasslands and oak woodland, mostly at elevations below 3,250’/1,000 m. Individual plants are usually (much) less than 18”/45cm wide but colonial and clumps rapidly to 3’/95 cm across. Subspecies (?) treleasii from southern Arizona is larger and with wider leaves than the nominate form. Some Arizona-based agave growers who have observed them in the field support the hypothesis proposed by Arizona Game and Fish (2005) that this is probably another natural hybrid (see A. x ajoensis below), but with A. chrysantha as the other parent. Images and written descriptions show that it lacks conspicuous leaf imprints and filaments on the leaf margins. This taxon is rare in cultivation.
The species is exceptionally cold hardy to 0-5 degrees F/ -17.8 to -15 C. The nominate subspecies is locally common to abundant in native ecosystems across its range. Very drought tolerant but looks best with supplemental water in the summer. Not a great candidate for pot culture but makes an interesting addition to the xeriscape. Outside of plantings in regional botanical gardens, possibly the least-cultivated agave on this list.
A. x ajoensis = A. schottii ssp. schottii x A. deserti ssp. simplex. A rare and rather attractive natural hybrid restricted to elevations between 3,000-3,600’/900-1,100 m in the Ajo Mountains of Organ Pipe National Monument on the Arizona-Sonoran boundary. When not clumped, it can occasionally resemble a somewhat emaciated A. ocahui. Probably in a few private collections in Arizona and California, but otherwise only known to be in cultivation at the the Desert Botanical Garden in Phoenix.
There are also reports that this species may hybridize with at least one other sympatric Agave species in southern Arizona.
Agave colimana*. A localized, lightly-striped thread-leaf species growing to about 4’/1.20 m in diameter in nature, restricted to coastal cliffs and adjacent low-elevation foothills in southwestern Jalisco, Colima and extreme western Michoacán States. Still rather uncommon in cultivation and may be confused with some light-green ecotypes of the closely-related A. schidigera. My experience with this species is based on observations of plants in public gardens and a single plant purchased in 2017 from a southern Arizona nursery and put into the landscape in northern California. Not even as cold-tolerant as A. impressa, which occurs a few hundred miles (~500 km) north of the core populations of this plant. Tested to 30 degrees F/-1 C with minor leaf damage. Not a good pot plant because of its adult size. Besides ticking a box on a collector’s list, there is not a great deal to recommend this species when compared to A. impressa or A. schidigera. The names A. ortgiesiana and A. maritima are synonyms for this species sometimes used in the EU and México.
Agave felgeri. Mescalito. A small lowland desert species, originally collected on the edge of the Gulf of California near Guaymas, Sonora. Now restricted to the coastal plain of northwestern Sonora and isolated populations that persist near the Gulf. Small with rigid leaves. To about 12”/35 cm across, densely clustering, with pale leaf stripes and threaded leaf margins. Surprisingly cold tolerant, tested to 15-20 degrees F/-12 to -6.7 C in southern Arizona. Probably needs overhead protection from winter rains. Looks much nicer in managed small clumps than as massed colonies.
Agave filifera. Thread agave. Thread-leaf agave. This is a high elevation, central Mexican endemic that is easily confused with the wide-ranging, and sometimes considered conspecific, A. schidigera. This is the easternmost and highest elevation occurring member of the plants discussed here. Described from cultivated plants in Europe, it is now known to occur in Aguascalientes, Querétaro, Hidalgo and México states. A clumping species to about 24”/60 cm in diameter. Fast-growing for a species in this group. Better suited to landscapes than pots because of its colonial habit. Water and heat-stressed plants may show attractive red or purple tints to their leaves in high light environments and some specific ecotypes are now being offered by US nurseries.
There is a dwarf, sparely-offsetting cultivar in PTC, Agave filifera f. compacta that has small rosettes (to ~12”/30cm) with a relatively low number of wide leaves. ‘Cream Edge’ is a very handsome albomarginated clone in PTC.
Cold tolerant to at least 10-15 degrees F/-12 to -9.5 C.
An artificial hybrid, A. x leopoldii (= A. filifera x A. schidigera) is relatively common in cultivation. Smaller than both parents and with curlicued threads, it is usually photographed when potted as a single rosette but is annoyingly prone to recurve and clump. I found several clones amenable to highland tropical conditions as a fully exposed pot plant in Guatemala City. Because of its very untidy habit I see little to recommend it due to its rampant adult form. There is a variegated sport. Cold tolerant to 15-20 F/--9.5 C to -6.7 C
It is likely some plants labeled Agave filifera in cultivation under this name represent the following taxon.
Agave schidigera*. Thread-leaf agave. Occasionally considered a larger (to 36”/95 cm across), non-colonial subspecies or form of A. filifera, this wide-ranging taxon is a superb plant for pot culture and landscapes and will usually maintain a handsome, solitary form until blooming. Unlike A. filifera, this is a very widely-distributed and variable plant that occurs as a lithophyte throughout much of western México from northern Sinaloa to western Guerrero states at elevations from 1,600’-8,400’/~500 to 2,600 m. Some exceptional, heavily-marked clones such as ‘Durango Delight’, ‘White Stripe’ and the cream-tinted albomarginates like ‘Shiraito no Ohi’* (‘Queen of White Thread’ or f. compacta marginata) are among the most beautiful cultivated agaves. The winter-blooming inflorescences are also showy (see photo at the beginning).
Agave schidigera ‘Black Widow’ is a darker-colored, fairly compact clone from PTC. The rare, very showy ‘Sun Starr’, a f. medio-picta alba is an outstanding selection, as is the aureovariegated ‘Royal Flush’.
There are a few nondescript hybrids involving this species out there in “Agaveland” in addition to one very promising-looking hybrid made at Ruth Bancroft Garden, A. schidigera x ocahui, that definitely warrants wider distribution.
Cold tolerant to at least 15 F/-9.5 C.
Agave microceps*. Dwarf Thread-leaf agave. Separated from A filifera in 2007 this is a small striped and threaded species that appears restricted to steep volcanic slopes of a single locality in northern Sinaloa. Another easily confused species that bears quite a strong resemblance to the other miniature species discussed here. Some individuals show a distinct mid-stripe on their leaves. Still rare in cultivation but wild-collected seed does make its way from habitat on an infrequent basis and it is grown at several U.S. public gardens. This species is very suitable for pot cultivation due to its compact size at maturity (12”/30 cm). Probably limited cold tolerance to around 30 F/-1 C.
Agave multifilifera*. Hairy agave. Chahuiqui. Another plant that was formerly treated as an A. filifera subspecies in the past, but quite distinct overall. A mediopicta-type or lightly-striped plant that is extremely frondose with hundreds of narrow leaves having very filiferous margins as the name indicates. Offsets rarely and with great age. Large, to >5’/1.50 m wide x 3’/1 m tall, high elevation and presumably very cold tolerant from the northern Sierra Madre Occidental on the Sonoran-Chihuahuan border to northwestern Durango and northeastern Sinaloa from 4,500’ to over 6500’/1400->2,000 m. Can form a short trunk in nature over time. Although very slow-growing, not the best pot plant unless grown very hard; exceptional in the landscape. Requires full exposure and careful watering to maintain proper plant form. While unremarkable in youth, outstanding when mature. Cold tolerant to 15-20 F/-9.5 to -6.7 C.
Agave multifilifera ‘Starshine’ is a beautiful albomarginate clone in PTC with creamy-white leaf stripes.
Agaves hybridize readily in nature and cultivation, both in intra- and intersectional crosses. Some natural hybrids have stabilized over time, and several “species” known from the southwestern US and Mexico are now believed or known to be the product of hybridization. Examples discussed herein once believed to be full species that were later shown to be natural hybrids include A. x arizonica and A. x pumila. In artificial settings such as large gardens, public and private, where agaves can consistently grow to maturity, open-pollinated hybridization events occur routinely. Unfortunately, few are controlled, so the resulting offspring’s reported parentage is often just guesswork by collectors, nurserymen and their employees.
The two more common species of the Agave victoriae-reginae complex produce attractive and desirable hybrid offspring, some of which have been propagated in large numbers via PTC and sold as mass-market plants in the nursery trade. As far as I am aware, very few of them are the product of controlled crosses. The familiar A. nickelsiae x asperrima hybrids were discussed above. A couple well-known and widely-distributed hybrids have mysterious parentage that has not been fully sorted out even today. These plants are occasionally the subject of acrimonious online debate by agave aficionados and nurserymen.
The better-known Agave victoriae-reginae man-made hybrids are discussed below. All are widely misidentified, even (mostly?) by some well-known succulent nurseries. The differences can sometimes appear subtle, particularly when they are grown “soft”.
Agave ‘Blue Emperor’*. Probably the least controversial of the primary hybrids in cultivation in terms of its pedigree. Reportedly A. macroacantha x victoriae-reginae or the reverse cross and certainly looks it throughout its life. ‘Blue Emperor’ has a distinct glaucous cast to their blue-gray leaves when well-grown, small marginal teeth for much of their length, one to several visible tubercles on the lower leaf surfaces near the tip, and dark brown to glossy black apical spines. Rancho Soledad is reported to have introduced this plant into cultivation.
Terminal spines on all these plants hurt a lot if you get stabbed by one.
Agave ‘Little Shark’. Reported to involve the same parents and looks suspiciously similar in life, down to the presence of tiny tubercles on the lower leaf tips. Perhaps a sibling that was also propagated on, or just the same clone exhibiting the effects of a bit of mutation in PTC.
Agave ‘Royal Spine’*. True A. ‘Royal Spine’ is olive to dark green overall, lacks marginal teeth (although it does have tiny denticles along the leaf edges when young) and has broad, reddish to dark brown or black corneous leaf margins and stout, red or brown terminal spines. Tubercles absent from lower leaf tips. Reports indicate that this is also an A. victoriae-reginae x macroacantha cross but made with a green leaf form of the pollen parent. Different sources claim different origins for these plants. Moore (2016), Starr (2012) and others cite an employee at the Tropic World Nursery in Escondido, California as being the original breeder of ‘Royal Spine’ in the mid-1990s while some claim that it is a Rancho Soledad hybrid. It is not unlikely that several different crosses of the same species were made by different people in California over the years. Introduced to the commercial nursery trade by Allen Repashy from PTC. Reportedly susceptible to rot and collapse if over-watered as a pot plant.
Agave ‘Burnt Burgundy’*. Another older hybrid, putatively A. victoriae-reginae x palmeri and originating from seed collected off a plant grown at Gene Joseph’s Living Stones Nursery-Plants for the Southwest in Tucson, Arizona (fide G. Starr). Rosettes have markedly upcurved leaves in and small marginal teeth in youth, but mostly smooth leaf margins as an adult. Easily confused with A. ‘Blue Ember’ but, in my experience has proportionately narrower leaves, has fewer and smaller marginal teeth, and a more open rosette form.
Distinct glaucous banding is hard-wired into the genetic backgrounds of all five of these clones and is readily evident if soil and water conditions are even close to optimal. Despite some reports to the contrary, watering frequency does not influence the degree of banding on hybrid agave leaves. Bright exposure during spring, summer and early fall usually enhances both cross-banding and overall plant color.
Agave ‘Blue Ember’*. An artificial hybrid almost certainly involving A. victoriae-reginae, but recent claims have been made online by a breeder in southern California that A. potatorum x ocahui may be an alternative possibility. Distinct marginal teeth present along the length of the leaves. The terminal spines and leaf margin colors are variable (red through violet to black) depending on source and growing conditions. More than one clone may be in PTC and on the market under this name, either a sibling or from a remake of the cross. True A. ‘Blue Ember’ is another widely mislabeled cultivar. It is a very handsome plant and a worthy addition to any succulent collection. Be aware that there seem to be many photoshopped images of this clone published online, so not all plants have exquisite-looking powder blue leaves and hyaline, ruby red teeth and terminal spines.
Agave victoriae-reginae x ovatifolia (= A. x victorifolia) and A. ocahui x victoriae-reginae. These are fairly new, apparently controlled crosses made by nurserymen on both coasts with very limited releases. The second cross appears to have also been made in the EU. Rare in the trade. I have never seen a live example of either hybrid, but images on the internet show they are both interesting-looking. Images of a few open-pollinated hybrids that surfaced in an eastern Australia succulent nursery, reportedly of A. victoriae-reginae x parrasana, also appear online.
All of these hybrids are cold tolerant to at least 20 degrees F/-6.7 C, and most can handle moderately wet winters as well with minimal or no damage.
Besides deliberate obfuscation of parentage by some hybridizers to confound and stymie other agave breeders, it seems quite clear to me that random open-pollination events and sloppy record-keeping have also led to the confusion as to species involved in these crosses. In my opinion, all of the hybrids listed above are worth owning if you have the space. Note that individual conditions will often change the leaf color and (to a lesser degree) form of these plants. Several will also spread their wings towards >3’/95 cm spans as they mature and may also clump. Fortunately, most are reasonably slow-growing as pot plants, particularly if kept root-bound.
Other than the natural hybrids and Agave schidigera crosses mentioned previously, almost none of the other species discussed here have been used in hybridization for the nursery trade.
Pot cultivation. Most of the species listed above are eminently suited – for quite a few years at least – to pot cultivation on terraces, patio tabletops and windowsills. Light feeding and “hard’ culture will slow growth rates for species that are wider than 24”/60 cm in diameter as adults and keep them at manageable sizes. I have grown many species described here as young plants for over five years in a large, very bright bay window in California with excellent results.
Nurseries and many hobbyist growers prefer plastic pots over clays due to their lower cost, weight and strength, and many perfectly-grown plants have spent their entire lives in plastic pots. Having cultivated almost all my agaves in climates that experience heavy rain - late spring and summer in Guatemala and winter and early spring in northern California – I personally favor terracotta pots since the growing media can dry out faster.
Like most ornamental plants, agaves benefit from the use of high-quality water when grown in pots. Highly alkaline tap water can generate issues with nutrient availability and should be acidified or alternated with rain, bottled or reverse osmosis (RO) source water whenever feasible. Unsightly mineral deposits from the constant use of hard water are another reason to avoid over-reliance on poor quality municipal or well water sources. That said, acceptable-looking plants can be grown with municipal water in most areas. Given their origins, Agave colimana and A. felgeri are probably very salt-tolerant.
Growing media. I have always favored very high content of pumice in my succulent growing mixes to facilitate drainage and better atmospheric gas exchange with the roots. In Guatemala my source of organic matter was heat-sterilized, well-composted oak leaf litter. In California I generally use ProMix or similar. Ratios for medium-grade pumice to organic matter for plants grown indoors are 2:1 and outdoors 3:1 or even higher. I also amend these mixes with encapsulated gypsum, dolomite and balanced Nutricote 180-day formula. Growers with hard irrigation water can dispense with additional calcium sulphate and dolomite. Pure, clean hort grade pumice coupled with bottom heat is very useful for re-establishing valuable agaves that have lost their roots to rot.
In the landscape. Site plants carefully, taking into consideration their mature sizes, proclivity to clump, proximity to foot traffic and access for future maintenance. Prepare beds for planting by amending heavy soils with pumice or other light aggregates, add slow release granulated fertilizers to the hole, blend with prepared soil and tip plant out of pot into it. Tamp soil firmly around the base of the plant. Agaves should be planted with their “necks” slightly higher than the surrounding soil level (i.e. mounded) to allow for natural subsidence and to keep the base of the stem dry. Do not plant them in depressions where their bases will stay permanently wet. This is not quite as important in arid climates than it is in areas that receive a lot of rainfall but is a good general rule for growers everywhere.
The use of boulders as thermal mass/heat sinks that radiate stored warmth when the sun goes down is very useful when trying to improve the chances of marginal plants in temperate and subtropical landscapes. Besides the aesthetics, I like to site cold temperature sensitive species against basalt and black lava outcrops to give them the benefit of irradiated warmth overnight on the chilly predawns of late fall and winter.
Periodic drenches of fungicides designed for control of fungus in turf planting, etc. (e.g. Banrot) are of great value in wet climates. Not an endorsement. Use common sense when using any pesticide and always follow label instructions and local laws.
Hail. I have suffered a few very severe hail strikes on my outdoors succulent collections over the past several decades. In agaves, evidence of damaging hail storms is usually left in the form of many small, light-colored “fractured” spots (technically referred to by horticulturalists as “dings”) on the upper leaves that are oriented on a fully horizontal plane. Species with rather brittle or glossy leaves, such as A. impressa, A. pelona, A. guiengola, A. chazaroi, etc. usually show the damage much more conspicuously than the rugose-leaf species like A. parryi, A. guadalajarana, A. potatorum, etc. I like to follow up these stressful events with sprays of broad-spectrum contact fungicides with surfactants, but in dry climates these are probably unnecessary. If you’re unlucky enough to get a visit by large-bore hail, hope that it occurs while your plants are still fairly young; time (and new leaf production) heals all wounds.
Non-specific rots and leaf spotting, including anthracnose (Colletotrichum spp.) and lookalikes. In the real world, hobbyists and most nurserymen don’t continually fire samples off to their local agricultural extension office’s lab for positive identification of every suspected pathogen that surfaces in their inventory, so “shotgunning” broad spectrum fungicides or antibiotics seems the order of the day. Cleary’s 3336 or Daconil + mancozeb fungicidal drenches at labeled rates or sprays to runoff in combination with together a spreader-sticker will usually halt the spread of many leaf spots, etc. A couple of passes will usually dry things up unless the climate is really being uncooperative. I also favor removal of leaves showing a lot of active rot with a clean cutting tool. Sterilize between cuts with a burner, TSP or alcohol. Syringe cut areas with hydrogen peroxide, let dry, then dust with fine powdered horticultural grade or activated charcoal. See above recommendations about responsible and legal ag-chem use.
Agave snout weevils (Scyphophorus acupunctatus) and running bugs (Caulotops barberi) . These often very problematic critters are largely a problem where native agaves occur in the desert U.S. southwest, but they can be invasive and other true bugs are occasionally pests elsewhere. I’ve never seen them on my plants in Guatemala nor in northern California, but I understand they are a problem in the landscape further south. Various treatment protocols are published online and in print, but as a general recommendation for landscape growers, watch out for any evidence of snout weevil infestations in your area and respond accordingly if you have large specimen-sized or flowering agaves in your collection.
Mealybugs (Pseudococcidae, many genera). These sucking insects are an ubiquitous pest of agaves grown indoors. There are several non-toxic options for treatments of minor infestations in a small collection, including soapy water and dilute alcohol dabs. Any potent, broad-spectrum insecticide that is labelled for sucking insects will usually control mealies. Systemics as drenches work particularly well in controlling both mealies and scale insects during the growing season. Avoid oil-based products for spraying agaves.
Agave mites (Eriophyidae, genus uncertain). Now a relatively minor headache following the development of chemical control protocols, agave mites were a major challenge to U.S. agave growers about a decade ago. Outbreaks of agave/eriophyid mites in private collections can almost invariably be tracked back to introductions of unquarantined plants from nurseries that don’t have them under control. They concentrate in the meristem and produce leaf damage in the form of unsightly scarring and irregular patches of discolored, “oily”-looking leaf tissue. They can also kill plants if left unchecked. There is a great deal of (mis) information on how to eradicate these pests on the internet, unfortunately, some of it from sources who don’t understand eriophyid mite control. Since few of the products required to successfully combat agave mites are readily available to amateur growers, and two very effective miticides are quite costly even on a per spray basis, I won’t discuss these particular products other than to say that best practices dictate that THREE separate pesticides with different modes of action and whose labels advertise translaminar absorption are required for thorough control. I quarantine new plants for several months and all receive at least two full spray cycles (usually three) prior to being introduced to my general collection. Several flushes of healthy, undamaged leaves are indicative that the infestation has been eradicated. Note that a few sources online suggest that eriophyid-infested agaves will stop offsetting. This is not always true, and I have seen several large A. nickelsiae with fresh eriophyid mite damage that continued to offset prior to, during, and following treatments made over a several month period.
Left, oily staining and older leaf damage on a recently-purchased Agave pablocarilloi. Right, more conspicuous older damage with accompanying leaf staining on an Agave nickelsiae that had previously gone through a full treatment cycle on my end involving several recommended pesticides. This particular plant later flushed completely clean leaves and its appearance has greatly improved since this photo was taken in mid-2017.
Over the past couple of years, I received more than a few agave mite-infested agaves from two very reputable US cactus and succulent nurseries that I have purchased plants from over the years (see images above for two examples) and that I know use chemical control measures, as well as one that apparently doesn’t. Due to high inventory rotation and overlooked “back benches”, things can slip through the cracks in the best-run nursery or public garden. Because of this, no-one gets a pass from me anymore.
Casual collectors should take pains to inspect agaves prior to purchase and only buy ostensibly clean examples that are not jumbled up together with questionable-looking ones. Due to the relatively high cost of eradicating agave mites in an individual plant, the most practical solution for most hobbyist growers is to simply discard any suspect or infested plants. Beyond that, strictly quarantine and treat all incoming agaves and closely-related plants to valued, established collections with several recommended miticides in rotation, full stop.