Orchid types

Some authors, e.g., Dahlgren et al. (1985), recognized three families of orchids based on the number of anthers of androecium: Apostasiaceae, with two or three anthers only partially fused to the gynoecium; Cypripediaceae, with two anthers fused to the ovary; and Orchidaceae, the richest family in number of species, which features a single anther fused to gineceo.

However, all molecular evidence to date shows that Orchidaceae defined or circumscribed in this way would be polyphyletic. Morphological and molecular data indicated, however, that they should be defined as large Orchidaceae, thus a new classification of the family that corresponds to the known phylogeny was published by Chase and collaborators in 2003, which recognized five subfamilies, which are described below.

Apostasioideae

Apostasioideae orchids are considered the most primitive group of orchids. They have either two or three stamens in their flowers, which are “regular,” and resemble the genus Hypoxis (Hypoxidaceae family). The leaves are arranged in a spiral on the stems, are folded, and resupinate (except for Apostasy). The embryo sac is bisporic, and Allium type.
The basic chromosome number is x = 24. Apostasioideae includes only two genera (Apostasy and Neuwiedia) and approximately sixteen species.

Synonym: Apostasiaceae Lindley, Neuwiediaceae Reveal and Hoogland.

Cypripedioideae

This second group of orchids is an independent lineage, with taxonomic category subfamily: the Cypripedioideae. This group also retains primitive features, such as the presence of two stamens in the flowers. It comprises five genera: Cypripedium, Mexipedium, Paphiopedilum, Phragmipedium and Selenipedium, and has about 150 species which are distributed in five monotypic tribes. They are widely distributed in Eurasia and across America.

This group is known popularly as the “shoe lady” because of the inflated slipper-shaped lip that functions as an insect trap; this is because the insect is forced to the back by the staminode, where pollinia are collected and deposited. In these orchids, two fertile anthers are arranged on each side of the column.

The central stamen is sterile, and is curiously modified as a shield that prevents pollinators from having direct access from the front of the flower to the middle. The other two stamens are hidden behind the staminode.

The lip saculi form has evolved as a trap for pollinators. The inner walls of the lip are very slippery, but there is a ladder of hairs lying inside the dorsal wall. This leads from under the stigma ventral to one of the two exits at the base of the lip on each side of the column.

Synonym: Cypripediaceae Lindley

Vanilloideae

Vanilloid orchids are a small group that includes Vanilla, a genus of about seventy species of lianas. It comprises fifteen genera and 180 species distributed in moist tropical and subtropical strips of the globe and in the United States of America.

Orchidoideae

This subfamily includes mostly terrestrial orchids with fleshy tubers or rhizomes. The type genus Orchis and “bee orchid” (Ophrys, so called because its labellum seems like the abdomen of a bee) belong to this group. It comprises 208 genera and 3,630 species distributed worldwide, except for the driest deserts, the Arctic Circle, and Antarctica. The representative members of Orchidoideae include Cynorkis, Diuris, Goodyera, Habenaria, Orchis, Platanthera, Spiranthes, and Zeuxine.

Epidendroideae

This group is made up of more than 500 genera and about 20,000 species, which are located in the same regions as Orchidoideae, although some subterranean species are also in the Australian desert. Epidendroideae contains many tropical epiphytic, and representative genders include Bulbophyllum, Catasetum, Dendrobium, Epidendrum, Encyclia, Maxillaria, Oncidium, Pleurothallis, and Vanda.

The delimitation of genera in this group is notoriously problematic, and the most numerous genera are not monophyletic. Most are tropical epiphytes (usually with pseudobulbs), but some are terrestrials and even a few are saprophytes.