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Key to Crotalaria

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1 Leaves trifoliolate; either a decumbent or ascending perennial herb to 1 m tall, or an erect annual herb, typically 1-2 m tall.
..2 Leaflets 0.7-1.2 (-3.0) cm long; legume 10-15 mm long, ca. 4 mm in diameter; corolla 7-9 mm long; [perennial, native (though sometimes weedy)]
..2 Leaflets 1.5-5 (-6) cm long; legume14-45 mm long, 4-17 mm in diameter (either or both substantially longer or wider); corolla 8-20 mm long; [annual, alien].
....3 Leaflets lanceolate, often narrowly so, 3-15× as long as wide; legume straight or nearly so (or upcurved at the tip).
......4 Corolla 8-10 mm long; legume 4-6 mm in diameter, upcurved at tip
......4 Corolla 18-20 mm long; legume 15 mm in diameter, not upcurved
....3 Leaflets obovate to elliptic-oblong, 1.5-3.5× as long as wide; legume either straight or conspicuously curved.
........5 Legume straight, 10-15 mm in diameter, pilose; stem pubescence spreading
........5 Legume conspicuously curved or straight, 5-12 mm in diameter, minutely puberulent; stem pubescence appressed
..........6 Legume conspicuously curved, 5-6 mm in diameter; inflorescence bracts caducous; calyx 6-8 mm long, with short, appressed hairs
..........6 Legume straight, 8-12 mm in diameter; inflorescence bracts persistent; calyx 4-6 mm long, glabrous or with short, erect hairs
1 Leaves unifoliolate; plants of various habits, mostly either perennial, smaller, or both.
............ 7 Corolla 1.7-3.0 cm long; leaflets 4-15 cm long; stipules not decurrent on the stem and not conspicuously foliose; [exotic annual herbs, in disturbed habitats].
............ ..8 Legume glabrous.
............ ....9 Bracts of the inflorescence 2-3 mm long, caducous; leaflets 4-8 cm long
............ ....9 Bracts of the inflorescence 5-8 mm long, persistent; leaflets 5-15 cm long
............ 7 Corolla 0.7-1.4 cm long; leaflets 1-8 cm long; stipules of at least the upper leaves conspicuously decurrent on the stem, giving the impression of a downward-pointing arrowhead (this feature sometimes inconspicuous or essentially absent in C. maritima, C. rotundifolia, and C. avonensis); [native perennial or annual herbs, in natural or disturbed habitats].
............ ......10 Plant an erect annual; stems with spreading pubescence, the longer hairs 1-2 mm long; leaflets of the upper portion of the plant (4-) avg. 6 (-8)× as long as wide; [mostly of the Piedmont and Mountains (and Coastal Plain of VA)]
............ ......10 Plant a decumbent, sprawling, or erect perennial; stems with appressed or spreading pubescence, the longer hairs < 1.2 mm long; leaflets of the upper portion of the plant averaging either (1-) avg. 1-2 (-4)× or (5-) avg. 8-10 (-15)× as long as wide; [mostly of the Coastal Plain].
............ ........11 Leaflets glabrous above; leaflets of the upper portion of the plant usually (5-) 10 (-15)× as long as wide; plant erect or ascending
............ ........11 Leaflets pubescent above with strigose hairs (the hairs sometimes sparse – check with hand lens); leaflets of the upper portion of the plant usually (1-) 2-10× as long as wide; plant erect, decumbent, or low-ascending.
............ ..........12 Leaves uniformly linear (entire plant), mostly 1-1.5 cm long, ca. 2 mm wide; sepals reddish abaxially; plant bushy-branched; [coastal dunes, dry pinelands, s. peninsular FL, keys, north along the coasts, to Pinellas County on the west and Palm Beach County on the east]
............ ..........12 Leaves elliptic to ovate or orbicular (or if linear, only upwards on the stem), > 4 mm wide; sepals wholly green; plant sparingly branched; [of various dry, sandy habitats, collectively of e. MD south to s. FL, west to e. LA].
............ ............ 13 Stem pubescence of an overstory of spreading or ascending hairs 1.5-3 mm long (and longer than the stem diameter) and an understory of appressed hairs; leaf texture thin, herbaceous, fresh leaves flexible; leaf surfaces bicolored, the upper medium green, the lower distinctly paler, whitish-green; [pinelands and other dry sandy habitats, MD south to c. peninsular FL (Hernando, Lake, Volusia counties), west to e. LA]
............ ............ 13 Stem pubescence appressed-strigose, the hairs shorter than the stem diameter; leaf texture somewhat succulent, fresh leaves fragile, easily broken if bent; leaf surfaces unicolored, medium green.
............ ............ ..14 Stipules absent; keel beak short, slightly twisted towards the apex, curved back towards the standard; stems densely strigose with brown hairs; stems erect, to 12 cm tall, from a buried horizontal rootstock; [of Florida scrub in Highlands and Polk counties]
............ ............ ..14 Stipules present, linear, the free triangular portion ca. 5 mm long; keel beak elongate, spirally twisted, projected upwards and outwards; stems sparsely to moderately strigose with white or silver hairs; stems prostrate to ascending from a central rootstock; [of various xeric sandy habitats, e. SC south to s. FL, west to e. LA]
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