Bull. Torrey Bot. Club 28: 269. 1901.
Herbs, perennial, terrestrial, glabrous. Roots few, fleshy; tuberoids ellipsoid-ovoid. Stems simple. Leaves ephemeral, 2–6, basal; blade sessile, lanceolate to oblanceolate; cauline bracts ovate to linear-lanceolate. Inflorescences many-flowered racemes or spicate racemes. Flowers resupinate, white, yellow-green to green, nearly sessile; sepals 1–3-veined; lateral sepals similar, adnate to lip and slightly longer than free dorsal sepal; lip base adnate to column, blade simple, midrib thickened, broad; spur clavate to filiform; column short, auricles absent; anther 1, erect, connective narrow, cells close and parallel; pollinaria 2; pollinia 2, sectile; caudicles inconspicuous, attached to round to oblong viscidia; stigmas confluent, concave; rostellum 3-lobed. Fruits capsules, erect, nearly sessile, ellipsoid to sausage-shaped. x = 21.
Temperate regions, North America (including Mexico).
Species 10 (10 in the flora).
Piperia is perhaps the most taxonomically complex orchid genus in North America. Considerable variation occurs within most species, and distinctions among taxa are often subtle. In pressed, dried specimens important characteristics that otherwise may be obvious in the field are frequently obscured. Our views on the taxonomy of the genus evolved as more extensive field and garden studies have helped us interpret geographic patterns of variation and recognize additional unifying or distinguishing characteristics.
Leaf, bract, and floral measurements in the following descriptions represent the largest dimensions on a given plant.
|1||Spur 7–18 mm; viscidia ovate to oblong.||> 2|
|1||Spur 1–6 mm; viscidia broadly elliptic-ovate to rectangular-ovate.||> 6|
|2||Viscidia oblong, at least 2 times as long as wide; flowers white with green or yellow-green midvein; stem base usually thickened toward tuberoid.||> 3|
|2||Viscidia ovate to broadly elliptic or broadly oblong, usually less than 2 times as long as wide; flowers green; stem base uniform in diameter or attenuate toward tuberoid.||> 4|
|3||Spurs of most flowers straight, horizontal; stem 0.7–4.5 mm diam.; floral fragrance clovelike.||Piperia transversa|
|3||Spurs of most flowers curved, deflexed; stem (2–3)–12 mm diam.; floral fragrance musky or pleasant, not clovelike.||Piperia elegans subsp. elegans|
|4||Seeds usually blackish brown; lip triangular-ovate; petals erect-spreading; stem attenuate toward tuberoid.||Piperia michaelii|
|4||Seeds pale brown to cinnamon brown; lip lanceolate to broadly triangular; petals usually strongly erect-recurved; stem basally attenuate or not.||> 5|
|5||Petals falcate, ovate-attenuate, about 2 mm wide at base and 2–3 times as long; lip less than 2 times as long as wide; spur (7–)9–15(–18) mm; widespread.||Piperia elongata|
|5||Petals straight, linear, about 1 mm wide at base and 4–5 times as long; lip about 2 times as long as wide; spur 4–9 mm; not common, California.||Piperia leptopetala|
|6||Lip strongly recurved toward spur with age; flowers white or white and green; raceme rachis usually shorter than peduncle.||> 7|
|6||Lip straight or upwardly curved; flowers green; raceme rachis usually at least as long as peduncle.||> 9|
|7||Stem bracts usually fewer than 6; raceme ± secund; lip triangular-ovate; petals straight, white or with faint green midvein; c California to se Alaska.||Piperia candida|
|7||Stem bracts usually more than 6; raceme cylindric; lip triangular-lanceolate; petals erect, curved, green with white border; California.||> 8|
|8||Petals falcate, outer white border much broader than inner; stem base attenuate toward tuberoid; flowers weakly fragrant, never cinnamonlike, diurnal; Monterey Bay area, California.||Piperia yadonii|
|8||Petals straight-sided, inner and outer white border subequal; stem base swollen; flowers strongly cinnamon-scented, nocturnal; Point Reyes, California.||Piperia elegans subsp. decurtata|
|9||Spur shorter than lip, 1–2.5 mm; flowers scentless; leaves grasslike, erect, less than 1 cm wide.||Piperia colemanii|
|9||Spur at least as long as lip, 2–6 mm; flowers scented, at least at night; leaves not grasslike, prostrate to erect-spreading, usually over 1 cm wide.||> 10|
|10||Petals linear with slightly expanded base, about 4 times longer than wide, strongly upwardly recurved; lip narrowly lanceolate; spur attenuate, 4–9 mm; flowers with lemony scent or otherwise pleasant, not musky or honeylike.||Piperia leptopetala|
|10||Petals lanceolate to triangular-ovate, less than 3.5 times longer than wide, usually projecting to ± erect; lip triangular-ovate to lanceolate-elliptic; spur narrowly cylindric, blunt, 2–6 mm; flowers musky- or honey-scented.||> 11|
|11||Mature seeds blackish brown; flowers honey-scented; raceme rachis ± length of peduncle; stem attenuate toward tuberoid; Santa Monica Mountains to n Baja California, below 1500 m.||Piperia cooperi|
|11||Mature seeds tan to cinnamon brown; flowers ± musk-scented; raceme rachis usually longer than peduncle; stem diameter uniform or increasing toward tuberoid; widespread in North America but in s California occurring only above 1500 m.||Piperia unalascensis|