Heterotaxis

Heterotaxis
Heterotaxis sessilis
Scientific classification
Domain: Eukaryota Kingdom: Plantae Division: Magnoliophyta Class: Liliopsida Order: Asparagales Family: Orchidaceae Subfamily: Epidendroideae Tribe: Cymbidieae Subtribe: Maxillariinae Genus: Heterotaxis Lindl. 1826
Type species
Heterotaxis crassifolia Lindl. 1826
Species
14 species, see text
Synonym
Dicrypta Lindl. 1830 Marsupiaria Hoehne 1947 Pentulops Raf. 1836

Heterotaxis is a genus of orchids formed by a group of circa fourteen neotropical species which previously were considered part of genus Maxillaria. They are strong epiphytic plants with shiny dark green leaves which make a showy display making a very good first impression but 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, because they vary a lot and are much similar to each other, to diferentiate them is hard, with very few exceptions.

Distribution

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.

All species are mostly epiphytic, despite some hardly ever can 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 diferent environment conditions, since very wet forests of Florida and Amazon, to cloud mountain forests in the Andes and along Serra do Mar mountains in Brazil, and even in dry jungles of highlands of Central Brazil. 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.

Description

Heterotaxis are comparatively large and robust plants, usually of sympodial growth, with unifoliate lateraly compressed pseudobulbs, protected by several foliar stealths of almost always glossy foliage; or they can also lack pseudobulbs and have distical leaves, then growing simulating monopodial growth. All species have small thick flowers, which frequently do not open interely, ordinaryly yellowish, but also orange or white, sometimes with purple-bluish, lilac or brown-red spots. A thickening on the center of the lip is also common, sometimes it is covered by waxy trichomes that atract pollinators. Their column is very short. As all species once subordinated to Maxillaria the inflorescences are lateral and bear just one flower, and here are long, short or very short, in small numbers, ordinarily blooming more than once a year.

Taxonomic notes

John Lindley proposed this genus in 1826, when he described Heterotaxis crassifolia, its type species. Four years later, he described another new genus and species, Dicrypta baueri, which is today considered a synonym of the former. Within a few years, contemporary and subsequent taxonomists described or transfered 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.

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 e 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 restablishing the ancient genus Heterotaxis, the first proposed by Lindley. Both modern phylogeny and recent descriptions agree with the acceptance of this genus but, so far, nurseries and growers still use their former names and old synonymes, mostly Marsupiaria e Maxillaria.

Species

Some species of Heterotaxis are hard to identify. From the fifteen species submited to this genus, forteen are accepted but only six can be easyly recognized. Moroever 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 disjuction of the areas it does exist. This wide distribution originated several very closely related species that when com from close areas are very hard to separate. For instance, if we start with the specimens that exist in Florida, they 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 beguins. 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 lenght of the leaves, shape and size of the pseudobulbs, shape of the calli on the labellum of their flowers, flower colors and lenght of the inflorescence. Different combinations of each one of this variations get different species names.

Despite the difficulties along this group of species derivated from 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.

• The one mentioned before can be called "Heterotaxis sessilis complex, it is characterized by pale yellow to bright yellow or orange flowers, with labellum of same colors or deeper, and short or long inflorescensces. They are eight species, Heterotaxis brasiliensis, Heterotaxis discolor, Heterotaxis fritzii, Heterotaxis maleolens, Heterotaxis santanae, Heterotaxis schultesii Heterotaxis sessilis, and Heterotaxis villosa.

• Heterotaxis violaceopunctata complex: species with pseudobulbs; withe ordinarily white flowers, exceptionaly yellow or cream, always with much darker labellum or sometimes spotted, generally of purple; and long or shortinflorescence. There are three species: Heterotaxis proboscidea, Heterotaxis superflua and Heterotaxis violaceopunctata.

• Heterotaxis valenzuelana complex: species withouth 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 inflorescensces. Two species belong to this group, Heterotaxis microiridifolia and Heterotaxis valenzuelana.

• Heterotaxis equitans. It 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, theis flowers are white or very light pale green, with labellum of very intense and dark blue-purple.

References

• R. Govaerts, M.A. Campacci (Brazil, 2005), D. Holland Baptista (Brazil, 2005), P.Cribb (K, 2003), Alex George (K, 2003), K.Kreuz (2004, Europe), J.Wood (K, 2003, Europe); World Checklist of Orchidaceae. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet accessed February 2009.
• Isidro Ojeda, Germán Carnevali Fernández-Concha & Gustavo A. Romero-González; New Species and Combinations in Heterotaxis Lindley (Orchidaceae: Maxillariinae) - Novon: A Journal for Botanical Nomenclature, Volume 15, Issue 4, pp. 572–582 (December 2005).
• Blanco, M. A. G. Carnevali, W. M. Whitten, R. Singer, S. Koehler, N. H. Williams, I. Ojeda, K. Neubig, & L. Endara. 2007. Generic Realignments in Maxillariinae (Orchidaceae). Lankesteriana 7(3): 515-537.
• Whitten, W.M., M. A. Blanco, N. H. Williams, S. Koehler, G. Carnevali, R. B. Singer, L. Endara, & K. M. Neubig. 2007. Molecular Phylogenetics of Maxillaria and Related Genera (Orchidaceae: Cymbidieae) Based Upon Combined Molecular Data Sets. American Journal of Botany 94: 1860-1889.
• Fábio de Barros, Notas taxonômicas para espécies brasileiras dos gêneros Epidendrum e Heterotaxis (Orchidaceae), Hoehnea 29: 112 (2002).