Middle American Epiphytic Cacti Part I: Disocactus and related
Epiphytic and hemiepiphytic cacti (Family Cactaceae, tribe Hylocereeae) are some of the most interesting understory plants of Neotropical ecosystems. They can be very conspicuous in some areas and range from mangrove thickets and Tropical Dry Forest (TDF) through lowland tropical wet forests and into lower montane cloud forests. Like many others in the family, this group of cacti remain a challenge for botanical fieldworkers and taxonomists and their names have been in a constant state of flux for almost 100 years. Opinions conflict quite a bit about “correct” names and some recent proposals are considered controversial. Several Mesoamerican genera are well-represented in both ornamental (orchid cacti) and commercial horticulture (dragonfruit), including Epiphyllum, Selenicereus, Hylocereus, Disocactus and Pseudorhipsalis. Some of these have been hybridized in cultivation at least since the early 19th century. Common names for more familiar species include orchid cactus, night-blooming cereus, Dutchman’s pipe cactus, rat’s-tail cactus, pitayas and epicacti as a generic term used by collectors. In parts of Central America, the ornamental species are known as “Galán de la Noche”. Their spectacular flowers make hybrid epiphytic cacti very popular with hobbyists and many societies exist worldwide dedicated to promoting their cultivation.
The four northern Central American species of Disocactus with terete or flattened crenate stems and colored flowers remain uncommon in cultivation and appear to be represented by very few captive clones in EU and U.S. collections. Ironically, the true species are more readily available in the EU than they are in the U.S., probably since German and Czech tillandsia enthusiasts have picked them up during their collecting jaunts to the region. They are excellent subjects for hanging basket cultivation and can be confined to 6-8”/15-20 cm containers for many years. Disocactus are easily propagated from stem cuttings but, like most (all?) epiphytic cacti species, are self-sterile so at least two clones are required for viable seed set. Access to pure seed from reliable sources remains elusive, so several very showy-flowered species are still very hard to find in cultivation.
Unfortunately, a quick web search of many of the species discussed here will show nurseries and private growers selling hybrid plants as “the real deal”. Collectors should look for material with good source origin from reputable suppliers (usually major botanical gardens) or impeccable matches to the species’ descriptions when acquiring these cacti. To further complicate matters for novices, it is obvious when looking at online herbaria records that there are also any number of misidentified dried plants in cabinets as well as a blizzard of erroneous locality reports. And finally, image searches for Disocactus species on the internet photo banks often reveal mistaken identities.
Note that all these cacti will hybridize promiscuously in cultivation where pollinators are present, so growers of pure species with good accession data should be aware that all open-pollinated fruit set on single clones will be parthenocarpic or of hybrid origin. Some of these garden hybrids will be very attractive (see below), but should be distributed as such, NOT as the maternal species.
Disocactus, like other Middle American epiphytic cacti, tend to flower heavily in the spring from early March through late May. This corresponds to the middle of the dry season and beginning of the rainy season for Mesoamerica. Off season flowers may also occur during the summer.
Most contemporary treatments for Disocactus have absorbed several very familiar cultivated genera, including Aporocactus, Heliocereus and Wittia. In 2016 a molecular phylogeny of Disocactus was published (Cruz, et. al.) that included just over a dozen species in the genus and confirmed the very close relationships between the cloud forest species whose distribution is centered in Guatemala that had previously been accepted based on flower morphology alone (Hunt, et. al. 2006). This publication also transferred several additional white-flowered species to Disocactus from Epiphyllum, a move that has been met with skepticism by some enthusiasts, but also supported the long overdue resurrection of the Mexican genus Aporocactus.
All these plants prefer rich, acid and very well-drained growing media with high percentages of perlite or pumice to facilitate rapid drying. Processed fine conifer bark, heat-sterilized leafy composts or “forest products” mixed at a 1:1 ratio work well for all of the epiphytic cacti I have grown over the decades. Wooden baskets with plastic screen or shade cloth inserts to prevent the media running out work well, as do standard plastic hanging pots and baskets. Epiphytic cacti can be heavy feeders when large and should be well-fertilized going into the blooming season. Time release fertilizers incorporated into new growing media should be supplemented with liquid feeds of balanced orchid fertilizers during the growing season. Plants in light dormancy during the winter benefit from drying out completely between watering and a steep reduction in the frequency of fertilization.
My interest in Disocactus is primarily focused on the species native to Guatemala, but I have also grown several others from southeastern Mexico and other parts of Central America.
In 1962, famed American botanists Paul Standley and Louis Williams wrote of this species in the monumental “Flora of Guatemala”:
“This plant was considered by the senior author, whose experience in Guatemala has been exceeded by no other botanist, to be one of the most attractive plants of all Guatemala. The flowers, though small, are produced in great abundance, making the plant conspicuous from some distance, and they are of a lovely shade of rather pale reddish purple…”
I have also seen very large examples of this species in full flower on cloud forest edge near the type locality at San Martín Sacatepéquez-Chile Verde, Quezaltenango during the dry season and agree that they are a stunning spectacle in nature.
Described in 1944 as Bonifazia quezalteca, in a monotypic genus erected by Paul Standley and Julian Steyermark for this remarkable epiphytic cactus. Previously considered to be endemic to a very small area in the volcanic highlands of southwestern Guatemala between about 5,500-6500’/1,700 and 2,000 m, it has since been collected just over the border at similar elevations in southeastern Chiapas, México and has also been reported at a locality in the uplands of south-central Guatemala. It is known to occur proximate to D. biformis on the southern slope of Volcán Siete Orejas in Quezaltenango Department, but the two species are separated by an almost 1,600’/500 m elevational gap. Images stored online on the iNaturalist site of putative “D. nelsonii” growing wild in Motozintla, Chiapas, México strongly resemble the flowers of the known artificial hybrid discussed here under D. x Vista Hermosa.
This species, together with its sibling taxon D. echlamii exhibit unique flower morphologies for the genus, having tubular corollas with exerted stamens and styles. They differ from each other not only in flower color (pink or light purple versus carmine red), but also in that D. quezaltecus has recurved corolla tubes. The authors of the recently-described D. salvadorensis (Cerén, et. al. 2017) from Cerro Montecristo in Santa Ana Department of El Salvador place that plant alongside these two species. However, its admittedly variable flower morphology appears closer to D. biformis, which is restricted to cloud forests on the Pacific versant of western and south-central Guatemala. For many years, preserved specimens of this form stored at La Laguna Botanical Garden in San Salvador were (mis) identified as D. nelsonii ssp. nelsonii. The extreme and unparalleled variability in corolla form and color for the genus strongly suggests a bird-dispersed, hybrid origin for D. salvadorensis. The presence of D. eichlamii and D. biformis in the uplands of southeastern Guatemala, coupled with the known diversity of sympatric white flowered Epiphyllum (Disocactus) species such as E. crenatum (= D. crenatus in Cruz, et. al.) there makes these very probable candidates for parent stock for this plant. Many species of Nearctic and local avian migrants are known to feed on the fruits of Hylocereeae cacti species, most notably tanagers (Thraupidae; personal observation), making them possible dispersal agents. A hybrid origin would also partially explain the genetic makeup and corolla color variability of D. salvadorensis reported by the authors.
I suggest that the recently-described Disocactus salvadorensis should be re-evaluated as a naturally occurring hybrid population involving at least two epiphytic cactus species native to the region, possibly D. biformis and Epiphyllum crenatum (D. crenatus).
Described in 1911 as a Phyllocactus by Wilhelm Weingart, it was transferred to Disocactus in 1913 by American botanists Nathaniel Britton and Joseph Rose. Over the years, its identity and status has been confused by a number of botanists, including Standley and Williams who wrote, “Probably one of the more common Epiphyllums in Guatemala”. Quite the contrary, it is one of the least common epiphytic cactus species in the country! I have only found D. eichlamii in high elevation cloud forest at ~6,200’/1,900 m in south central Guatemala, but it is reported at a wide elevational range from 3,250 -9,100’/1,000 to 2,800 m at a number of localities in the central and southeastern parts of the country. It can be locally common at a few highland localities, but appears to have a spotty distribution across its known range. Surprisingly, it can still be found in forest fragments relatively close to the capital and can persist in degraded habitats. The upper elevational reports would make it, together with the widely-distributed Disocactus speciosus ssp. cinnabarinus, the highest elevation epiphytic cacti species occurring in Central America. Its bright red or carmine, tubular corollas are very conspicuous in canopy when the plants are in flower, and it certainly deserves wider cultivation.
Images of cultivated Disocactus eichlamii flowers may be seen here: https://cactiguide.com/cactus/?genus=Disocactus&species=eichlamii
The first species discovered from this group, originally described by John Lindley in 1843 as Cereus biformis, but transferred to Disocactus by him in 1845. It was introduced to cultivation in Cornwall, England in 1839 by plants sent by the famous Guatemala-based orchid collector, George Ure Skinner, erroneously labelled as from “Honduras”. This origin locality was subsequently assumed by some to mean “British Honduras” (Belize), but it now appears that Skinner got his localities mixed up, intentionally or otherwise. This species is known from several Guatemalan stations where he collected, so it is almost certain that the type material originated from there. It was in cultivation elsewhere in Europe by the 1850s and first flowered in Kew Gardens in 1874. There are several versions of hand-colored plates published of it in late 19th century botanical texts and magazines that are posted online. Now known to be endemic to southwestern and central Guatemala, it is a striking species in cultivation, notwithstanding its rather small flowers. As is evident from the image here, large specimen plants are spectacular when well-flowered. Easy in cultivation but becomes large, leggy and woody with time; older plants require annual stem pruning to maintain good plant form.
Disocactus nelsonii ssp. hondurensis
The nominate subspecies was originally described as a Chiapasia in 1923 by Britton and Rose in their classic monograph on the Cactaceae. Like other monotypic genera erected by others for what are now known as Disocactus species, their peers dicarded Chiapasia in favor of Epiphyllum in short order.
Disocactus nelsonii ssp. hondurensis is a very beautifully-flowered, isolated form of the species endemic to premontane tropical forests of the Caribbean versant of northern and central Honduras. The subspecies was described by Myron Kimnach in 2002, based on a specimen collected near Siguatepeque, Comayagua Department. It is separated from the nearest population of the nominate subspecies, which occurs in middle elevation cloud forests of the Pacific versant of western Guatemala and eastern Chiapas, by well over 200 miles/320 km airline. Unlike that plant, ssp. hondurensis is still very rare in cultivation. Flowers are larger, much fuller and generally more attractive in this subspecies than those seen in the Mexican and western Guatemalan populations. As far as I am aware, molecular work has not been done on this taxon and I suspect that it is an excellent candidate as a standalone species (i.e. D. hondurensis). Limited collections indicate that this cactus grows as both a lithophyte and epiphyte and is restricted to a fairly narrow elevation range between 1,600-2,600’/500-800 m in warm, wet tropical forests.
Disocactus x Vista Hermosa
This beautiful hybrid of two plants originating from collections made in middle elevation cloud forests in Quezaltenango Department derives from a hummingbird-pollinated event in my garden in Guatemala earlier this decade. The seed parent is the D. biformis shown here and the pollen parent is a D. quezaltecus clone also shown above. The resulting hybrid plants are very vigorous and fast-growing, and branch early in life. The flowers blend both color and form of both parents well, have good substance and last almost a week in perfect condition. Several seedlings have been grown on from this cross in the U.S. and all are quite uniform in appearance.
Excluding the trio of white-flowered Epiphyllum species (E. angulifer, E. crenatum and E. lepidocarpum) that Cruz, et. al. somewhat controversially resolved as Disocactus, the following species are now recognized as valid for the genus:
D. ackermannii (two subspecies)*
D. nelsonii (two subspecies)*
D. speciosus (five subspecies)*
*Species marked by an asterisk have been grown by the author.
From images that I have seen taken in nature in both El Quiche and Zacapa Departments of Guatemala, it appears that there are at least two undescribed Disocactus taxa occurring in cloud forest on the Caribbean versant of Guatemala. I would also expect that there are novel members of this genus awaiting discovery/description from elsewhere in Mesoamerica.
Pseudorhipsalis amazonica, the Disocactus that wasn’t
One of the most commonly-cultivated “collectors” epiphytic cacti that occurs in the area is Pseudorhipsalis amazonica, a beautiful lowland species that has the confusing taxonomic history typical for this group. It has been known relatively recently as Wittia amazonica, W. panamensis, Wittiocactus amazonicus and Disocactus amazonicus. It is widely but discontinuously distributed from the TDF in the Pacific lowlands of northwestern Costa Rica through the Caribbean lowland rainforests of Panama and western Colombia, south through premontane habitats in Ecuador to the Amazonian departments of Perú. There are also isolated populations on the Caribbean coast of Venezuela and inland in the southwestern parts of that country. It has handsome, uniquely colored tubular corollas and is hummingbird pollinated like most of the day-flowered species. Some wild populations appear to have uniformly magenta-colored flowers rather than the two-tone corollas shown here. Cultivated plants grown under shaded conditions can produce pale pink or whitish flowers. The widely disjunct populations of this plant across a vast expense of Central and South America suggest that it may indeed represent more than one valid species. Three subspecies (amazonica, panamensis and chocoensis) have been described but this arrangement is not universally recognized by botanists.
This species is of easy culture and can remain root-bound in a 10-12”/25-30 cm pot for several years with no ill consequences. Plants flower best when large and can be grown as hanging plants or pot plants on a bench or patio. Very light shade and warm temperatures are preferred, but the species is cold tolerant to at least the mid-40s F/7s C if kept on the dry side in winter.
For collectors of cloud forest plants, especially bromeliad, orchid and Neotropical blueberry enthusiasts, these are especially attractive and easily grown additions to a garden, sun room or greenhouse.