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Orchidaceae
See list of 21 genera in this family-
1a. Labellum deeply concave to saccate (at least in the basal portion), forming a small to very evident pouch [Fig. 164]
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2a. Labellum saccate in only the basal portion, 1.8–12 mm long; inflorescence a spike or raceme, with 5–72 flowers [Fig. 166]
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3a. Principal leaves all basal, usually white-striped or white-reticulated [Fig. 165]; labellum white to white-green
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3b. Principal leaves borne on the stem, alternate, without white markings; labellum purple to purple-brown with pink near the apex or dark red
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2b. Labellum saccate ± throughout, 10–67 mm long; inflorescence a solitary flower or a spike-like raceme with 2 or 3 (–4) flowers
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4a. Labellum with 2 apical horns and a prominent fringe of yellow bristles; plants with 1 leaf; flowers with 1 fertile anther; stem arising from a corm
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5a. Labellum basally prolonged into a hollow spur (the spur short and saccate in Coeloglossum) [Figs. 173,175]
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6a. Flowers bilaterally asymmetrical (i.e., appearing lopsided); leaf single, abaxially purple, produced in autumn, withering by early spring, therefore, the flowering plants without well-formed leaves
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6b. Flowers bilaterally symmetrical; leaves 2 or more, less commonly single, abaxially green, produced in spring and present during flowering
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7a. Labellum white with magenta spots, 3-lobed, the middle lobe notched at the apex; leaf single, basal
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7b. Labellum not spotted, variously shaped but never 3-lobed with a notched middle lobe; leaves 1–several, basal or arranged on a stem
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8a. Stems conspicuously angled; labellum unlobed, typically white and strongly contrasting in color from the pink-magenta sepals and lateral petals (rarely all the perianth of similar color); viscidia enclosed in a single, 2-lobed bursicle
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8b. Stems terete; labellum unlobed, lobed, or fringed, ± similar in color to the remainder of the perianth (those Platanthera with 2 basal leaves usually have the sepals more strongly tinged with green than the petals); viscidia free, not enclosed in a bursicle
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9a. Labellum 3-lobed, the middle lobe much shorter than the lateral 2 [Fig. 161]; viscidia covered by membranes; orifice of spur covered by a membrane with a small opening; floral bracts conspicuous, usually evidently exceeding the flowers
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9b. Labellum variously shaped but never 3-lobed with a very reduced middle lobe [Figs. 172,173,174]; viscidia not covered by membranes; orifice of spur open; floral bracts inconspicuous to (rarely) shortly exceeding the flowers
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10a. Labellum simple, sometimes with apical teeth or a marginal fringe, but without 3 evident lobes (in part)
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10b. Labellum clearly lobed into 3 segments
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11a. Labellum 5–25 mm long, fringed on the margin [Fig. 174]; leaf blades entire (in part)
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11b. Labellum 3.5–5 mm long, with entire lobes; leaf blades denticulate
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5b. Labellum lacking a spur (flowers with a small, inconspicuous, adnate spur in Corallorhiza formed by the 2 lateral sepals) [Figs. 167,170,177]
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12a. Flowers not resupinate, the labellum the uppermost petal; labellum with a conspicuous brush of yellow-tipped hairs; leaves articulated, this appearing as a thin, transverse line near the base of the leaf
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12b. Flowers resupinate, the labellum the lowest petal; labellum with or without hairs or ornamentation of some type; leaves not articulated
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13a. Leaves whorled at the summit of the stem
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13b. Leaves or scales alternate or opposite, borne at base of plant and/or distributed along the stem
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14b. Flowers subtended by rather inconspicuous, usually scale-like bracts; labellum ornamented or not, never with 3 parallel, green ridges
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15a. Flowers large, the labellum (12–) 17–35 mm long; flowers usually solitary
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16a. Leaves flat, numbering 1–3 on the stem, present at anthesis, the largest 7–25 (–32) mm wide; sepals and lateral petals distinct, the outer spreading
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16b. Leaves obscurely plicate, solitary on the stem, not fully formed at anthesis, 2–4 (–12) mm wide; sepals and lateral petals connate at the base, the outer erect
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15b. Flowers smaller, the labellum 1.3–12 mm long; flowers 3–180 per inflorescence
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17b. Principal leaves 1–several, borne at base of plant and/or distributed along the stem; labellum entire or 3-lobed, without a single apical notch (with a prominent notch in Malaxis, but then with a small lobe at the base of the central notch) [Figs. 169,176]
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18a. Flowers predominantly white or cream (except for a yellow or green central area on the labellum in some species), sometimes tinged with yellow or green; leaves and stem bracts above them numbering 5 or more; labellum with a pair of basal callosities
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18b. Flowers not predominantly white or cream, variously colored and/or spotted; leaves and stem bracts (when present), numbering 4 or fewer; labellum without a pair of basal callosities
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19a. Plants leafless at flowering time, with sheathing bracts only, arising from coral-like rhizomes; plants without chlorophyll, the stems brown to purple, or yellow-green in one species
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19b. Plants with leaves at flowering time ( Aplectrum sometimes leafless at flowering, but the withered remnant usually present at stem base), arising from corms; plants chlorophyllous, the leaves and stems ± green at anthesis
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20a. Leaf solitary, evidently plicate, produced at distal end of corm in late season and persistent through the winter, usually withering by flowering; labellum white with magenta spots (rarely all white-yellow); capsules pendent
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20b. Leaf solitary or paired, not or only obscurely plicate, produced in spring, present during flowering, withering before winter; labellum green to yellow-green or brown-purple to pale purple, without spots; capsules spreading to erect
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21a. Plants with 2 leaves, in a pair near the base of the stem; labellum 4–12 mm long; capsules 9–13 mm long
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21b. Plants with a single leaf (rarely 2 and then not paired), borne on the stem; labellum 1.3–2.3 mm long; capsules mostly 5–8 mm long
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Each photo represents one genus in this family.