Epiphytic, lithophytic, or rarely terrestrial herbs, caespitose, sympodial or rarely monopodial and then usually branching above, erect, creeping or hanging. Roots fleshy, glabrous, terete to flat, sometimes rooting from nodes along the stem but usually only from the basal node on each sympodium. Stem usually cane-like, simple or branching, sometimes thickened and then fusiform, rarely pseudobulbous, branching basitonic or acrotonic, with or without predetermined renewal buds; if monopodial, monocaulescent or more often forming a branched crown, all shoots equivalent or some specialized for reproduction and others solely vegetative. Leaves one to numerous per stem, distichous, petiole tubular, sheathing, blade usually articulate and eventually deciduous or rarely non-articulate and then persistent, linear, ligulate, lanceolate, elliptic to ovate, rarely semi-terete, membranaceous, coriaceous to fleshy, green to variously blotched, lined or tinged with purple, margin entire or crenulate. Inflorescence apical, lateral, or rarely basal, if basal, the flowering shoot sometimes intercalated in the rhizome with the vegetative shoots, single-flowered, subcorymbose, racemose to paniculate, producing flowers only once, or new racemes from an old inflorescence over several years, thus producing in time a pluriracemose structure from what was a racemose inflorescence at first flowering (paracladial), sessile to long-pedunculate, when apical often produced from within one or two prominent spathaceous bracts that develop long before the inflorescence, or rarely at the same time and at the end of a flattened peduncle, the peduncle sometimes covered by imbricating, conduplicate bracts when lacking spathaceous bracts. Flowers resupinate or not, secund, helically arranged or distichous, and then often with the labellum facing the rachis, simultaneous or successive, perianth usually membranaceous, sometimes fleshy-thickened or stiff, mostly greenish yellow to white, sometimes brightly coloured yellow to red or pink to purple or black, often fragrant during a few hours of the day or night. Sepals subequal, usually free, sometimes partially connate, often dorsally keeled, especially the lateral sepals, partially spreading, spreading or reflexed, rarely forming a funnel-shaped flower, usually smooth, sometimes dorsally pustulate, muricate or verrucose. Petals usually narrower than the sepals, sometimes filiform, spreading, partly spreading, reflexed or pendent. Labellum mostly united to the column margins along the entire length of the latter, occasionally partially to totally free, forming a nectar tube that usually penetrates the ovary, the blade usually ornate with two basal, globose calli, a pair of laminar calli ending in a narrow keel, or a complex, tuberculate callus, occasionally lacking any callus, the blade sometimes with one or several parallel to radiating keels, sometimes ornate with trichomes or papillae, entire to deeply 3- or 4-lobed, mostly distinct from the sepals and petals. Column semiterete, straight to arcuate, when free sometimes with prominent involute column wings, rarely forming a column foot to form a basal sac with the labellum, rarely with a narrow cavity along the lower half of its ventral surface, clinandrium hood reduced or a funnel-shaped structure that may be tubular and much longer than the body of the column and then hiding the anther, apical margin entire to slit or fimbriate; anther dorsal to terminal, incumbent, reniform to ovoid, sometimes minutely papillose, occasionally with a horn-shaped process, 2- or 4-celled, pollinia two or four, obovoid, subglobose, laterally compressed to strongly ancipitous, in the shape of bird-wings, subequal to unequal, sometimes the inner pair much reduced; caudicles two or four, forming a pair, granulose to loose tetrads piled up, or laminar, cartilaginous in Neowilliamsia, shorter to about three times as long as the pollinia; stigma ventral, covering part to rarely the whole ventral surface of the column, a concave, sticky surface, usually with well-developed to protruding lateral lobes; rostellum apical, parallel to the longitudinal column axis and arching downwards at the apex, producing a semi-liquid viscidium attached to the caudicles of the pollinarium as it is removed from the column during pollination, leaving an elliptical slit, except in Oerstedella in which the rostellum forms a transverse sinuous structure that is not partly removed during pollination. Nectary usually a cuniculus, a deep tube penetrating part to the whole of the ovary, sometimes ventricose producing an inflated vesicle, when not penetrating the ovary sometimes forming a wide cavity between the labellum and column, rarely a sac, the nectary tube usually smooth, sometimes papillose or pilose, rarely producing nectar, the entrance to the nectary (keyhole) usually circular, rarely laterally constricted by thickenings of the column wings. Ovary unilocular, the placenta occupying the whole or part of it, then located at the base, in the middle or towards the apex. Capsule ellipsoid, pyriform to subspherical, three-ribbed, unilocular, often pedicellate with an apical neck, surface smooth to rarely muricate, sometimes winged. (EH, MS).
Epidendrum species are ubiquitous in the forests of tropical America, some even found in treeless areas such as sand dunes, scrub, and páramos. Epidendrum magnoliae is the only epiphytic orchid that occurs in the warm temperate, deciduous forests of southeast North America. Many species are entirely terrestrials, among them the groups including E. cernuum Kunth, E. chioneum Lindl., E. frutex Rchb.f., E. elleanthoides Schltr., E. pilcuense Hágsater, and E. dendrobioides Thunb. They are found in open vegetation in the Andean páramos and tepui vegetation, often on embankments or prostrate on shrubs. In these high-elevation species, such as E. cernuum, there is a main stem that grows unbranched during some years, which then produces several branches that flower profusely. Several species of the E. secundum group have a weedy habit, occupying open areas such as lake beds, steep slopes devoid of vegetation after landslides, roadside cuts, and sand dunes. Epidendrum radicans is common as a roadside weed in Central America, and E. calanthum Rchb.f. & Warscz., E. ibaguense, and the E. elongatum complex occupy similar habitats in South America. These species thrive in competitive habitats, and they have rapid germination and growth rates. Plants of E. radicans and E. secundum are known to produce flowers when they are only one year old, and their seeds are among the largest in the orchid family. After a few years of secondary succession, many cannot compete with species that subsequently invade. Ruderal habits are unknown in other groups of the genus. However, the vast majority of Epidendrum species are epiphytes and lithophytes that may constitute an important part of the epiphytic biomass in particular areas. They have adapted to almost all epiphytic biotopes of Neotropical forests except twigs. In Central America, some species are among the first orchids to seed into the upper branches of the crown, a restrictive environment with strong sunlight and little water and nutrient availability. Two of these successful species are E. cardiophorum Schltr. and E. isomerum Schltr. Many other Epidendrum species are humus epiphytes found in large branches and limbs. Epidendrum raniferum Lindl. and several species of the E. paniculatum complex grow in humus accumulations of tree crotches, where they can attain large sizes. In these species, biomass is often concentrated in the root system, and a particular stem may require up to three years to reach maturity and produce flowers. In contrast, some species are found on tree buttresses in the dark, humid environment of the forest understorey. These species are usually small, bark epiphytes with rudimentary waterstorage tissues, except for those in the thick leaves. Species such as E. macroclinium and E. allenii L.O. Williams fall in this category, sharing several traits that seem to be adaptations to this particular environment. Their stems have a strongly plagiotropic orientation, and flowering is slowly successive, usually with one flower open at a time. The raceme ceases development if a flower is pollinated, probably a mechanism for resource maximization. As an adaptation to dark conditions, the lower surfaces of leaves are suffused with purple anthocyanins that enhance photoassimilation (Lee et al. 1979). A different specialization is shown by some species growing on the small branches of the windy upper crown, such as E. cystosum Ames and some species of the E. incomptum, Oerstedella, and Neowilliamsia groups, although they are not true twig epiphytes. Some monopodial species such as E. ramosum, E. isomerum, and E. strobiliferum Rchb.f. are abundant in plantations (Catling et al. 1986). In pristine habitats they occupy the upper crown. Similarly, an orange-flowered species of the E. secundum group, E. portokalium Hágsater & Dodson, is common in the citrus and guava plantations in Amazonian Ecuador. A few Epidendrum species are found in ‘ant gardens’. Some of them are strictly myrmecophilous such as E. flexuosum G. Mey., but most are facultative and may be found in other microhabitats, More luxurious specimens, however, are found in ant nests, among them E. baumannianum, E. macrocarpum Rich., E. blepharistes Barker, and E. smaragdinum Lindl. This obligate and facultative ant symbiosis seems to be restricted to the Amphiglottis clade of Epidendrum. The ant nest provides a favourable, nutrient-rich habitat, and the insects give protection to the plant from other herbivores, whereas the root mass reinforces the ant nest. As in other members of the E. secundum group, high growth rates have been observed in E. flexuosum. Extrafloral nectaries are also widespread in the genus and attract ants, which are either prevented from entering flowers and damaging them or keep other herbivores from doing so (Delabie 1995). The ecological success of Epidendrum is apparently the result of the diverse array of vegetative architecture. Most Epidendrum species are sympodial, but in many others the sympodium is far from the substrate, permitting the plant to ‘explore’ parts of the tree crown, possibly exposing the foliage to better light. This exploration of the vertical space of the epiphytic biotope includes ascending and hanging species. The sympodium is ascending in the E. arbuscula group and the E. incomptum complex but pendent in E. parkinsonianum or E. vesicatum Lindl. In a few successful groups, the plants are monopodial with erect or long, hanging stems, as in the E. ramosum and E. imbricatum groups (subgen. ‘Strobiliferae’). Monopodial architecture in Epidendrum has evolved independently several times in the genus, associated to some degree with the existence of semelparous species. This phenomenon is observed in the E. platystigma Rchb.f. alliance and to a lesser degree in E. mixtum Schltr., E. ramosum and related species and also E. cernuum and its allies. In these plants there is a vegetative stage that may last several years. The monocaulescent architecture is similar to a Vanda plant. Initially it does not branch, but once the stem reaches an appropriate height, it produces subapical branches that eventually become numerous and produce a massive crown before the branches flower simultaneously. This mode is exemplified by E. paraguastigma Hágsater & García-Cruz, which may produce several thousand flowers on a single occasion and then die after fruiting. This is an extreme monocarpic event that fits the definition of semelparity. Loss of predictability of the position of the renewal bud, non-annual growth periods, modules specialized for either reproduction or vegetative functions, proliferation, and reiteration are some of the architectural specializations of the genus that should be considered key features that played an important role in the evolutionary history and ecological success of Epidendrum. Most of these adaptive traits are found in species of the wettest cloud forests. Some other Epidendrum species are true xerophytes with notable adaptations to dry conditions. In seasonal habitats, a few species such as E. miserum Lindl. and E. longicaule are deciduous and bear foliage only during the rainy half of the year. The E. schlechterianum Ames complex are small plants with succulent leaves, similar to some crassulaceous plants, and E. parkinsonianum leaves have an expansion zone, increasing the number of cells in the mesophyll (Baker 1972). In other lowland species from seasonal habitats, pseudobulbs are more common. Other means of water storage include the fleshy roots of the E. anisatum group, the unifacial, equitant leaves of E. lockhartioides Schltr. and its allies, and the terete leaves of some Lanium species. (EH, MS).
Epiphronitis Veitchii was one of the first orchid hybrids produced, involving Sophronitis coccinea (Lindl.) Rchb.f. and E. radicans. However, Epidendrum has not been much favoured by orchid breeders, although E. x O’Brienianum is a common pot plant in many subtropical areas. Several species of the E. secundum group have been used in horticulture for hedges and were used by Goodale Moir in Hawaii to produce other hybrids that produce flowers year-round. There are several cases of these plants having escaped cultivation in Florida, Puerto Rico, and Jamaica, and herbarium records exist for them in Uganda, Sri Lanka, and elsewhere. Some of these species have also been used to produce intergeneric hybrids, in particular E. radicans. Epidendrum pseudepidendrum has been used in hybrids as a source of orange and green colours and for the ‘plastic’ quality of the lip, and E. ilense Dodson for the large fringed lip. Epidendrum medusae, with its large red flowers, has also been tried, but the resultant muddy colour is not attractive. Generally the plants are large, cumbersome, and small-flowered. As the generic name Epidendrum has been retained in horticulture for hybrids of segregated genera, especially Encyclia and Prosthechea, there are numerous hybrid genera that do not correspond to true Epidendrum hybrids, especially in Epicattleya, Epilaelia, Epilaeliocattleya, Brassoepidendrum, and many multigeneric hybrids. (EH, MS).