keys to the vascular plants of east texas - Botanical Research ...

754 ORCHIDACEAE
Spiranthoideae), and Vanilloideae (Judd et al. 2002). Representatives of four of the subfamilies
(all except the basal, Old World Apostasioideae) occur in East TX. The family has been variously
considered to be in either Liliales or Asparagales, with recent molecular evidence suggesting
that Orchidaceae are a monophyletic group in the Asparagales (a group containing
Agavaceae, Amaryllidaceae, Iridaceae, Hypoxidaceae, etc.) (Chase et al. 1995b; Dressler & Chase
1995; Fay et al. 2000; Davis et al. 2004). “The extraordinary diversity of the orchids has only
been fully realized during the last 150 years, yet orchids are mentioned in the earliest botanical
literature as sources of wonderment or medicinal power. The well known belief in the powers
of the testicle-like tubers of Orchis was described by Dioscorides in his De Materia Medica (c.
AD 70). …” (Rasmussen 1999). Even earlier, Theophrastus (327–285 BC) described orchids (in the
genus Orchis) in his Enquiry into Plants. Orchids are particularly abundant in the tropics
where many species are epiphytic. Atwood (1986) indicated epiphytes account for 73% of the
family, and many of these have special swollen water and nutrient storage structures called
pseudobulbs (modified stems)—a particularly important adaptation for the epiphytic habit.
The family is extremely important horticulturally for its beautiful and intricate flowers, and
nearly 100,000 hybrids have been reported (Huxley et al. 1992), including numerous intergeneric
hybrids. However, “most of the plants traded in the national and international market belong
to a small number of species and their hybrids in only a few genera” (Romero-González et
al. 2002). Orchid cultivation is very old, dating back over 2,500 years. Kung-fu-tzu (Confucius
551–479 BC) said “Acquaintance with good men is likened to entering a room full of Lan.” “Lan
gives the king’s fragrance.” Lan is the Chinese term for “fragrant Orchid” and refers to Cymbidium
ensifolium (and C. pumilum), which had apparently been brought into cultivation
long before the time of Kung-fu-tzu (L. Magrath, pers. comm.). Well known cultivated genera
include Cattleya (CORSAGE ORCHID), Cymbidium, Dendrobium, Epidendrum, Paphiopedilum
(SLIPPER ORCHID), and Phalaenopsis (MOTH ORCHID). In addition to hybridization, tissue culture
and other sophisticated techniques are now used in orchid propagation and cultivation. The
fruit of Vanilla planifolia Jackson, a tropical American spice used by the Aztecs and earlier
Mexican cultures, is the source of the flavoring vanilla. While huge numerically and of great
importance horticulturally (Cullen 1992), the Orchidaceae remains one of the least understood
families of flowering plants (Pridgeon et al. 1999) for a variety of reasons (e.g., lack of good fossil
record, size, largely tropical distribution).
Pollination mechanisms are often incredibly specialized (e.g., pseudocopulation in which the
flower mimics a female insect and thus attracts males who carry out pollination while attempting
to copulate with the flower); some species even imprison and intoxicate their pollinators.
Other species offer no reward and attract pollinators by deceit (Neiland & Wilcock 2000).
Pollinia are often attached by their sticky viscidia to particular body parts of insect visitors (e.g.,
compound eyes, head, proboscis) and subsequently transferred to the flowers of other individuals
(see Catling & Catling 1991b for detailed information on orchid pollination). Special relationships
with mycorrhizal fungi are necessary for seed germination, seedling growth, and nutrient
uptake (see e.g., Clements 1988; Anderson 1991; Currah 1991), and mycotrophy (= obtaining food
from decaying organic material via a special relationship with a symbiotic fungus) is either a
primary (Corallorhiza, Hexalectris) or secondary source of nutrition. Orchidaceae are unique
in having basidiomycete fungi involved in the mycorrhizal relationship (Currah 1991). A number
of orchids have a low tolerance for environmental disturbance (probably in part due to their
obligate relationships with mycorrhizal fungi and in most cases specific pollinators), and many
species are now greatly reduced in number or extinct due to habitat destruction and modification.
However, some species, particularly those of bogs and wetland pine savannahs, require
natural disturbance such as fire. Finding orchids in the wild can sometimes be difficult. According
to Yatskievych (1999), “Many species produce only vegetative growth some years and
several regularly take breaks from aboveground life, persisting subterraneously for one or more
years.” Of the 55 species of orchids known for TX (Liggio & Liggio 1999; J. Liggio, pers. comm.),