perennial, sometimes with rhizomes or corms. Roots mycorrhizal (receiving
nutrients from a symbiotic relationship with soilborne fungi), often fleshy,
sometimes thickened and tuberlike. Aerial stems erect to spreading. Leaves
mostly alternate or basal, rarely opposite or whorled, parallel‑veined,
the bases sheathing the stems. Inflorescences spikes, racemes, or panicles, or
the flowers 1 per stem. Flowers usually subtended by bracts, zygomorphic,
perfect (uncommonly unisexual elsewhere), often twisted 180° at the base during development so that the top of the flower is
oriented toward the bottom at maturity (resupinate). Sepals 3, free or
with 2 sepals fused together, green or other colors. Petals 3, usually not
green, free or less commonly with 2 petals fused, 1 differentiated from the
other 2 into a lip of various shape and size, this appearing as the lowermost
petal in resupinate flowers. Stamen 1 (2 fertile stamens and 1 staminode in Cypripedium),
fused to the stylar column on the side opposite the stigma and separated
from it by an expanded lobe of tissue known as the rostellum (except in Cypripedium).
Pollen grains (except in Cypripedium) fused into 1–6 saclike masses (pollinia)
per locule of the anther, each with 1 end tapering into an elongate tip with a sticky pad (viscidium).
Ovary 1 per flower, inferior, with 1 locule. Style 1, fused with the stamens
into a usually thickened stylar column. Stigma 1; 2‑ or 3‑lobed.
Fruits capsules dehiscing by 3(6) longitudinal slits. Seeds numerous, dustlike,
short‑lived, the embryos mostly undifferentiated. About 600 genera, about
15,000 species, worldwide.
Orchidaceae are one of the largest families of flowering plants. The greatest
diversity of genera and species is in the tropics, where epiphytic species are
common. Although many interspecific hybrids have been described within the
family, these mostly involve tropical genera, and there is apparently
relatively little hybridization among temperate, terrestrial species. The
delimitation of genera below follows Dressler’s (1993) excellent review of the
highly modified flowers of the orchids are adapted to pollination by various
insects. The pollinia become attached by the viscidia to insect visitors and
are subsequently deposited on the stigmatic lobes when the pollinator visits
another flower. The pollination syndromes involved are often complex, and the
flowers often can only be pollinated successfully by particular kinds of
insects, such as butterflies, fungus gnats, small, native bees, or particular
groups of moths. Data on pollinators cited in the species treatments mostly
originated from Catling and Catling’s (1991) review of breeding systems and
pollination in North American orchids.
orchids in the field can be a most challenging experience. Many species produce
only vegetative growth some years and several regularly take breaks from
aboveground life, persisting subterraneously for one or more years. A
population of Platanthera praeclara in northwestern Missouri was thought
to have become extirpated, but flowering plants reappeared eight years after
the initial find. The life histories of most North American orchids are as yet
poorly understood, and even how long most plants live is unknown for most species.