ORCHIDACEAE (Orchid Family)

Plants 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^[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.

The 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 family.

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.

Finding 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.

Many species in Missouri occur in relatively small populations and produce few fruits. Overcollection and modifications to their habitats, such as changes in soil moisture, light levels, and density of competing vegetation, have undoubtedly contributed to the present rarity of some species. All orchids have obligate relationships with soilborne, mycorrhizal fungi and do not tolerate environmental changes well. Thus, orchids generally do not transplant well into gardens. Collectors also should avoid disturbing rootstocks and should consider photographic documentation of populations rather than herbarium specimens, as most species can be determined readily from habit and closeup photographs.