Heterotaxis is a genus of orchids formed by a group of circa fourteen epiphytic neotropical species which previously were considered part of genus Maxillaria. Most of the species are robust plants with shiny dark green leaves which presents a showy display making a very good first impression but that end disappointing because of their small flowers, usually yellow, which, because of their short inflorescences, hide between the foliage and can hardly be seen. Although the species that belong to this genus are easy to identify as members of it, because several species are highly variable and some species are very similar to others, to differentiate them is hard. The limits between each species not seem well established, with few exceptions, thus the concept of some species sometimes overlap others. Among all Heterotaxis species, H. equitans is a favorite of orchid collectors because it has visible and showy white and dark blue-purple flowers; and H. valenzuelana is sometimes collected due to the uniqueness of their fan shaped foliage.
The range of distribution of Heretotaxis is wide, particularly because of the type species, H. sessilis, which can be found from south Florida, Caribbean and Mexico, spread through all Central America countries to tropical America, reaching Bolivia and south Brazil. Two other species have a wide range of distribution: Heterotaxis equitans, found through several countries in Central South America, and H. valenzuelana which exists from Costa Rica to Ecuador and Venezuela, Caribbean and southeast, south and central regions of Brazil.
Few species are endemic or distributed for limited areas like Heterotaxis fritzii, which just exists in Ecuador; H. maleolens in Costa Rica; H. microiridifolia in Peru; H. santanae, in Venezuela and French Guyana; and H. schultesii in Amazon Forest, nearby Urubu River in Brazil.
All species are mostly epiphytic, despite some can occasionally be seen living as litophytes on shady and humid cliffs. The species of Heterotaxis hardly ever are found living under full sunlight, being more common under the shelter and shade of trees. They are strong plants that can adapt to different environment conditions, since very wet forests of Florida and Amazon, to cloudy mountain forests in the Andes and along Serra do Mar mountains in Brazil, and even in dry jungles of highlands of Central Brazil, however, most of the species live in warm humid equatorial and tropical forests. Some species, like Heterotaxis equitans can be found also living at the edges of the jungles were the get more light than most of other species of this genus.
Heterotaxis species are easy to grow provided they are potted in a well drained substrate, able to get dry few hours after watered, under medium light, in a well ventilated place preferably humid, or at least humid during the night hours.
- The floral pedicel is wider than the other internodes of the peduncle.
- The junction of the column and the pedicel is slanted at an angle of 45º.
- The sepals and petals have a subapical mucron.
Heterotaxis are comparatively large and robust plants among orchids. According to their morphologic characteristics they can be split into two main groups, identifiable at the first glance, all bearing comparatively minute flowers growing from several or few inflorescences produced sequentially from each leaf axil, almost any time of the year. As any species once subordinated to Maxillaria the inflorescences are lateral, they hardly are taller than the pseudobulb and often are very short, bearing just one flower. All species have small thick flowers, which frequently do not open entirely, ordinarily yellowish, but also orange or white, sometimes with purple-bluish, lilac or brown-red spots. A thickening or variable calli on the center of the lip are common, sometimes covered by waxy glandular trichomes that attract pollinators, mostly meliponine bees. Their column is very short and the fruits show lateral dehiscence.
The core group of Heterotaxis species present sympodial growth and short rhizomes, with unifoliate laterally compressed, minutely wrinkled, pseudobulbs, protected by several foliar stealths of glossy foliage. The pseudobulbs are minutely wrinkled bearing one leaf at the apex, of varied thicknesses, sometimes purple underside, which may be very long or sometimes shorter, depending on the species or whether when the plants receive plenty of light. Here belong the majority of the species and the type species.
The second group entirely lacks pseudobulbs, showing a pseudomonopodial growth with flat distichous leaves. One species, Heterotaxis equitans has ascending habit and is vegetatively very similar to some Vanda and Angraecum species. The other species, which the most noted member is Heterotaxis valenzuelana have very long rhyzome and their leaves are highly flattened forming a sort of fan, thus can be vegetatively compared to Ornithocephalus species. The leaves of this later subgroup, unlikely all the other Heterotaxis species, are not glossy; they seem to be covered by white dust. Because these obvious vegetative differences Frederico Hoehne proposed the genus Marsupiaria for them in 1947.
The genus Heterotaxis corresponds to a group of plants previously classified as Maxillaria subgen. Heterotaxis; Maxillaria sect. Heterotaxis; Maxillaria sect. Iridifolieae; yet encompassing the concepts of genera Dicrypta and Marsupiaria.
The first species to be described which now belongs to the genus Heterotaxis was Epidendrum sessile by Olof Swartz, in 1788, over a plant found in Jamaica. At that time, few were the orchid genera already described and most of epiphytic orchids were then described under the genus Epidendrum. The genus Maxillaria, where all Heterotaxis species described later were classified during almost two centuries, just was described in 1794 by Ruiz and Pavón, The species descriptions at the time were very simple and the one made by Swarts consisted of only four lines.
Only thirty eight years later, in 1826, John Lindley again received a plant from Jamaica and decided to propose the genus Heterotaxis for it. The plant he received and described as Heterotaxis crassifolia, the type species of its genus, happened to be the same Swarts had described earlier, however, for some reason Lindley missed Swarts description. Four years later, he described another new genus and species, Dicrypta baueri, which is today considered yet another synonym of the same species. In 1839, Lindley received from Demerara, Guiana, another species which he found similar to Dicrypta baueri although with the underside of the leaves of deep purple color and flowes orange with a callus almost all along the center of the lip. He denominated this species Dicrypta discolor. Within a few years, contemporary and subsequent taxonomists described or transferred all known species to Dicrypta. During the decade of 1850, Heinrich Gustav Reichenbach decided that there was no reason enough to maintain these species separated and moved them all to Maxillaria.
As mentioned before, in 1947 the Brazilian Botanist Frederico Carlos Hoehne suggested a new genus, Marsupiaria, to subordinate the species lacking pseudobulbs. Later taxonomists, such as Garay, Senghas, Brieger, Illg and Pabst, followed Hoehne and, one by one, along the years, subordinated all species of this group today known to Hoehne's genus.
Finally, Fábio de Barros published a review in 2002 reestablishing the ancient genus Heterotaxis, the first proposed by Lindley. On this publication he reinstates the former name of the type species and makes five new combinations. Three years later Ojeda and Carnevale, supported by phylogenetics studies, added eight species more to the genus, six were new name combinations of previously described species and two were new ones.
Heterotaxis most closely related genera, both also once considered to be part of a large genus Maxillaria are Nitidobulbon and Ornithidium. Both the flowers of Heterotaxis and Nitidobulbon are distinctly fleshy usually possessing fiber bundles in the sepals and petals.
The Brazilian taxonomists Hamilton Brieger and Dieter Illg considered Nitidobulon nasutus as a member of Heterotaxis group, but this species belongs to a separate clade along with N. cymbidioides.
Despite morphologists and phylogenists are in agreement with the new classification of these fourteen species, so far nurseries and growers keep using their former names and old synonyms, mostly Marsupiaria e Maxillaria.
From the fifteen species submitted to this genus, fourteen are accepted but only six can be easily recognized. Moreover there is no consensus about the real number of species to be accepted, according to the reference this number varies and different species are accepted. This is a result of the wide range of distribution of Heterotaxis sessilis, and the disjunction of the areas it does exist. This wide distribution originated several very closely related species that, when found in close areas, are very hard to separate. For instance, the specimens that exist in Florida are a little bit different from the ones of Mexico, the ones from Mexico, a little bit from the ones of Panama, and so forth, thus, when two plants from very distant places are compared they show many differences although there is a continuous change and numerous variations in the middle, making very hard to establish when a species ends and another one starts. Heterotaxis sessilis may be considered in fact a superspecies, or as it is named today, a complex of cryptic species. The variations one can see among all these closely related species are, thickness and length of the leaves, shape and size of the pseudobulbs, shape of the calli on the labellum of their flowers, flower colors and length of the inflorescence. Different combinations of each one of this variations get different species names.
Despite the difficulties along this group of species related to H. sessilis, not all Heterotaxis species are so confusing and some are actually very easy to recognize. Heterotaxis can be divided in four clearly distinct groups.
Heterotaxis sessilis complex is characterized by pale yellow to bright yellow or orange flowers, with labellum of same colors or deeper, and short or long inflorescences. They are eight species, Heterotaxis brasiliensis, Heterotaxis discolor, Heterotaxis fritzii, Heterotaxis maleolens, Heterotaxis santanae, Heterotaxis schultesii, Heterotaxis sessilis and Heterotaxis villosa.
The story of some synomyms of Heterotaxis sessilis was mentioned before, but it is even longer and more complicated. Frederico Hoehne and João Barbosa Rodrigues identified a common species from the southeast Atlantic Forest of Serra do Mar mountains, as Maxillaria crassifolia, and Barbosa Rodrigues described another species, Maxillaria villosa, for the species existing on northern region states. Later, Porsch, confused by the similarity of both, cited the later to São Paulo seashore. Hoehne himself commented that was not sure if the later and Heterotaxis villosa were on not synontms of Heterotaxis crassifolia. Alexander Curt Brade described a variety of Heterotaxis villosa with purple leaves that seems to be exactly Heterotaxis discolor.
In 1977, Brieger and Illg, concluding that the species from Serra do Mar, which shows longer and wider leaves, besides slightly larges pseudobulbs, was not the same Maxillaria crassifolia from Central America and described Maxillaria brasiliensis for this variety.
As mentioned before, there is also Dicrypta discolor, described by Lindley, which shows very few differences, mostly on the color of the leaves and on the labellum, which additionally has a continuous callus whiule the other species have the labellum lighter colored with small dots and the callus separated in two, one close to the baso of the lip and another to their apex.
In 2005 it was described Heterotaxis fritzii, another variety from Ecuador but with very thick and narrow leaves of triangular section. In 2007, Mark Whitten revised this genus and accepted all species but Heterotaxis crassifolia which is a synonym of Heterotaxis sessilis, although he affirms more research is needed to limit every species.
Heterotaxis violaceopunctata group is formed by three species with pseudobulbs; with ordinarily white, yellow or cream flowers, always with much darker labellum or sometimes spotted, generally of purple; and long or short inflorescence. There are three species: Heterotaxis proboscidea, Heterotaxis superflua and Heterotaxis violaceopunctata, which have flowers with white segments minutely dotted of lilac and darker labellum.
Also in this group there was some confusion to identify the species. Barbosa Rodrigues described Dicrypta longifolia, which, being homonym of a previous one, was renamed by Hoehne as Maxillaria tarumaensis. now considered a synonym of Heterotaxis superflua.
Heterotaxis valenzuelana group is formed by two species without pseudobulbs, the plants are fan shaped; pale yellow to bright yellow or orange flowers, with labellum of same colors or deeper, and short or long inflorescences. Two species belong to this group, Heterotaxis valenzuelana and Heterotaxis microiridifolia that is a similar but smaller species.
Heterotaxis equitans is a very distinctive species of neotropical orchid for this plant looks like very much with monopodial species from Asia and Africa. They do not have pesudobulbs, their flowers are white or very light pale green, with labellum of very intense and dark blue-purple.
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