Flora of the Southeastern United States
2022 Edition

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Key to Oxalis

1 Leaflets 1; [s. TX southwards]
1 Leaflets 3; [collectively widespread].
..2 Leaves pinnately trifoliolate; plants perennial herbs or shrubs; [s. TX southwards]
..2 Leaves palmately trifoliolate; plants annual or perennial herbs; [collectively widespread]
....3 Plant acaulescent; leaves basal; flowers white, pink, or purple.
......4 Leaflets strongly 2-lobed, each of the 6 lobes of the 3 leaflets > 2× as long as wide
......4 Leaflets notched at the apex, but not deeply so, the 6 lobes <1.5× as long as wide.
........5 Leaflets obdeltoid (the apical lobes angular, each leaf thus with 6 "points").
..........6 Leaflets green; flowers pink, blooming mainly spring-summer; plants with bulbs and bulblets; leaflet apex usually truncate
..........6 Leaflets purple or green; flowers white, blooming mainly in the winter; plants with scale-clad rhizomes; leaflet apex usually deeply notched
........5 Leaflets obcordate (the apical lobes rounded, each leaf thus with 6 rounded lobes).
............ 7 Flowers solitary (rarely in simple umbels of up to 5 flowers); plants either rhizomatous (O. montana) or bulbous (O. brasiliensis and O. hispidula); tips of sepals plane; leaflets lacking oxalate deposits (visible as dots)
............ ..8 Flowers strictly solitary; [plants native]; [section Oxalis]
............ ..8 Flowers solitary or in simple umbels of 2-5 flowers; [plants non-native of disturbed situations]; [section {}].
............ ....9 Abaxial leaf surface sparsely but evenly strigose with fine hairs; leaflet margins glabrous to sparsely irregularly ciliate with loose, fine hairs; outer bulb scales 5-8 (-13)-nerved; sepal apices without orange tubercles; aerial propagules sometimes produced at bracteole region of scape
............ ....9 Abaxial leaf surface strongly strigose to hirsute-strigose; leaflet margins prominently ciliate with stiff, sharp-pointed hairs; outer bulb scales 3- (-5)-nerved; sepal apices with a pair of elongate orange tubercles; aerial propagules never produced
............ 7 Flowers in umbels; plants bulbous; tips of sepals with orange callosities; leaflets with oxalate deposits (visible as dots) distributed either evenly over the entire surface, around the margins of the leaflets, or at the apical notch of the leaflets; [section Ionoxalis].
............ ......10 Sepals conspicuously appressed-pubescent; leaflets with reddish-brown callosities mostly along the margins; [naturalized]
............ ......10 Sepals glabrous or sparsely pubescent; leaflets with reddish-brown callosities either scattered over the surface or only at the apical notch; [native or naturalized]
............ ........11 Leaflets 25-45 mm long; leaflets with reddish-brown callosities scattered over the surface; [naturalized]
............ ........11 Leaflets 8-15 mm long; leaflets with reddish-brown callosities only at the apical notch; [native]
............ ..........12 Flowering Aug-Sep (-Oct); leaves present Oct-May; [in longleaf pine woodlands and Coastal Plain outcrop glades / woodlands]
............ ..........12 Flowering (Mid Feb-) Apr-May (-Jul); leaves present Mar-Oct; [widespread in our area]
....3 Plant caulescent; leaves alternate; flowers yellow; [section Corniculatae].
............ ............ 13 Stems evenly strigose from base to peduncles and pedicels.
............ ............ ..14 Flowers 1-3 (-8) in umbelliform cymes; flowers homostylous; petals 5-12 mm long, yellow, without red lines
............ ............ ..14 Flowers (2-) 3-5 (-8) in umbelliform cyme; flowers distylous; petals (6-) 12-16 (-17) mm long, yellow with prominent red lines in the corolla throat
............ ............ 13 Stems pilose to villous to nearly glabrous, rarely strigose and then only on peduncles or pedicels.
............ ............ ....15 Petals 9-20 (-23) mm long, red-lined in the throat (sometimes very faintly so).
............ ............ ......16 Corolla throats strongly red-lined within; petals 9-20 mm long; flowers 1 or (2-) 3-8 in umbelliform cymes above the level of the leaves; stems densely and pilose with stiffly spreading non-septate hairs; stoloniform rhizomes lignescent or ligneous and numerous on an individual plant
............ ............ ........17 Petals 9-15 mm long; plants cespitose or weakly colonial; pedicels strigose with short hairs that are curved towards pedicel apex
............ ............ ........17 Petals (13-) 15-20 (-23) mm long; plants strongly colonial; pedicels villous with long straightish hairs
............ ............ ......16 Corolla throats yellow, very faintly to strongly red-lined within; petals 10-18 mm long; flowers 1 or 2-4 (-8) in regular or irregular cymes, above or within the level of the leaves; stems nearly glabrous to sparsely or densely pilose or villous with septate hairs or a mixture of septate and non-septate hairs; stoloniform rhizomes usually 1 or few, herbaceous or lignescent.
............ ............ ..........18 Plants arising from slender, lignescent, stoloniform rhizomes without tubers; leaflets with upper shoulders usually rounded, margins often with a narrow purple margin; flowers produced above the level of the leaves; petals 10-14 mm long, throat yellow to very faintly or weakly red-lined within
............ ............ ..........18 Plants arising from slender, herbaceous, stoloniform rhizomes at intervals producing white, horizontal, fusiform tubers or tuberlike thickenings; leaflets with upper shoulders flattened, margins green; flowers produced mostly within the level of the leaves; petals 12-18 mm long, throat strongly red-lined within
............ ............ ....15 Petals 4-9 (-11) mm long, yellow, without red lines in the throat.
............ ............ ............ 19 Stems repent, rooting at most nodes; seeds brown, transverse ridges not white; stipules oblong with distinct flanges and free auricles
............ ............ ............ 19 Stems erect, usually arising singly from the base, rarely decumbent, not or very rarely rooting at the nodes, from a short, thin, often herbaceous to slightly lignescent rhizome etc. ; seeds all brown or with white transverse ridges; stipules absent or so reduced to be barely evident.
............ ............ ............ ..20 Stems (5-) 8-30 (-35) cm, sparsely pilose with non-septate hairs to almost completely glabrous, arising from a taproot, often producing lignescent stolons; flowers 1 or 2 (-3, rarely 4-5) in umbelliform cymes; capsules glabrous to sparsely puberulent, not villous
............ ............ ............ ..20 Stems 20-60 (-90) cm long, sparsely to very sparsely pilose with nonseptate hairs or a mixture of nonseptate and septate hairs or densely villous with septate hairs, arising singly from the base from a short herbaceous to lignescent rhizome; flowers usually (3-) 5-7 (-15) in regular (rarely irregular) cymes; capsules villous to puberulent and villous to glabrate