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Published In: Genera Plantarum 64–65. 1789. (4 Aug 1789) (Gen. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

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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.

 

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1 No leaves present at flowering time (except for bracts subtending the flowers), the aerial stems lacking chlorophyll or appearing so (2)
+ Plants in flower with 1 or more foliage leaves, the aerial stems green or partially green (6)
2 (1) Flowers with a conspicuous spur; vegetative leaves (appearing after flowering time and overwintering) ovate-triangular to heart-shaped 16 Tipularia
+ Flowers lacking a free spur; vegetative leaves not produced, or if produced then elliptic to linear in outline (3)
3 (2) Perianth all white (except sometimes with a green or yellow area on the inner surface of the lip); flowers in a spirally twisted spike or spikelike inflorescence 15 Spiranthes
+ Perianth yellow, red, or purple, sometimes with the lip white, but the lip then usually with red or purple spots; flowers short- or long-stalked in racemes, not produced in a twisted, spiral pattern (4)
4 (3) Sepals 18–21 mm long; the lip 14–16 mm long, with about 7 prominent, longitudinal ridges 9 Hexalectris
+ Sepals 3–15 mm long; the lip 2.5–12 mm long, with 1–3 low, longitudinal ridges (5)
5 (4) Sepals 10–15 mm long; the lip 10–12 mm long; vegetative leaves (appearing after flowering time and overwintering) elliptic in outline, dark green with white veins 1 Aplectrum
+ Sepals 3–8 mm long; the lip 2.5–6 mm long; vegetative leaves not produced 4 Corallorhiza
6 (1) The lip inflated, saclike, pouchlike or boat-shaped, the tip sometimes also lobed (7)
+ The lip not inflated, flat or curved (9)
7 (6) Flowers 1–3 per stem, the lip 20–50 mm long 5 Cypripedium
+ Flowers 5 or more per stem, the lip 3–10 mm long (8)
8 (7) Main foliage leaves alternate on the aerial stems; perianth green and purple 6 Epipactis
+ Main foliage leaves basal, the leaves of the aerial stems reduced to scalelike bracts; perianth white 8 Goodyera
9 (6) Flowers with a conspicuous spur (10)
+ Flowers lacking a free spur (12)
10 (9) Leaves 2, both basal 7 Galearis
+ At least 1 cauline leaf present (11)
11 (10) Corollas with the spur 1–3 mm long, up to 1/2 as long as the lip 3 Coeloglossum
+ Corollas with the spur 4–35 mm long, as long as or longer than the lip 13 Platanthera
12 (9) Plants with only 1 leaf at flowering time (reduced, scalelike leaves may also be present at stem base), this on the aerial stems (13)
+ Plants with 2 or more leaves at flowering time, these basal and/or on the aerial stems (15)
13 (12) Leaf oval to broadly elliptic; perianth green, minute, the sepals 1.3–1.5 mm long 12 Malaxis
+ Leaf linear to narrowly elliptic; perianth pink; perianth larger, the sepals 15–25 mm long (14)
14 (13) Flowers 2–10 per aerial stem, not resupinate, the lip positioned at the top of the flower 2 Calopogon
+ Flowers 1 or 2 per aerial stem, resupinate, the lip positioned at the bottom of the flower or nearly so 14 Pogonia
15 (12) Leaves in a whorl of 4–6 on the aerial stems 10 Isotria
+ Leaves alternate, opposite, or all basal (16)
16 (15) Leaves 2, both basal 11 Liparis
+ Leaves more than 2, or if 2 then at least 1 leaf on the aerial stem (17)
17 (16) Leaves 1 or 2, the largest (basal) one 30–90 mm long, lanceolate to narrowly elliptic; flowers 1 or 2 per stem, the perianth pink 14 Pogonia
+ Leaves 3–8, 6–18 mm long, narrowly ovate; flowers 2–6 per stem, the perianth white, sometimes tinged with pale pink or lavender 17 Triphora
 
 
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