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Key to Oxalis

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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, purple, or golden yellow.
      4 Flowers golden yellow.
      4 Flowers white, pink, or purple.
        5 Leaflets strongly 2-lobed, each of the 6 lobes of the 3 leaflets > 2× as long as wide
        5 Leaflets notched at the apex, but not deeply so, the 6 lobes <1.5× as long as wide.
          6 Leaflets obdeltoid (the apical lobes angular, each leaf thus with 6 "points").
             7 Leaflets green; flowers pink, blooming mainly spring-summer; plants with bulbs and bulblets; leaflet apex usually truncate
             7 Leaflets purple or green; flowers white, blooming mainly in the winter; plants with scale-clad rhizomes; leaflet apex usually deeply notched
          6 Leaflets obcordate (the apical lobes rounded, each leaf thus with 6 rounded lobes).
               8 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)
                 9 Flowers strictly solitary; [plants native]; [section Oxalis]
                 9 Flowers solitary or in simple umbels of 2-5 flowers; [plants non-native of disturbed situations]; [section {}].
                   10 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
                   10 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
               8 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].
                     11 Sepals conspicuously appressed-pubescent; leaflets with reddish-brown callosities mostly along the margins; [naturalized]
                     11 Sepals glabrous or sparsely pubescent; leaflets with reddish-brown callosities either scattered over the surface or only at the apical notch; [native or naturalized]
                       12 Leaflets 25-45 mm long; leaflets with reddish-brown callosities scattered over the surface; [naturalized]
                       12 Leaflets 8-15 mm long; leaflets with reddish-brown callosities only at the apical notch; [native]
                          13 Flowering Aug-Sep (-Oct); leaves present Oct-May; [in longleaf pine woodlands and Coastal Plain outcrop glades / woodlands]
                          13 Flowering (Mid Feb-) Apr-May (-Jul); leaves present Mar-Oct; [widespread in our area]
    3 Plant caulescent; leaves alternate; flowers yellow; [section Corniculatae].
                            14 Stems evenly strigose from base to peduncles and pedicels.
                              15 Flowers 1-3 (-8) in umbelliform cymes; flowers homostylous; petals 5-12 mm long, yellow, without red lines
                              15 Flowers (2-) 3-5 (-8) in umbelliform cyme; flowers distichous; petals (6-) 12-16 (-17) mm long, yellow with prominent red lines in the corolla throat
                            14 Stems pilose to villous to nearly glabrous, rarely strigose and then only on peduncles or pedicels.
                                16 Petals 9-20 (-23) mm long, red-lined in the throat (sometimes very faintly so).
                                  17 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
                                    18 Petals 9-15 mm long; plants cespitose or weakly colonial; pedicels strigose with short hairs that are curved towards pedicel apex
                                    18 Petals (13-) 15-20 (-23) mm long; plants strongly colonial; pedicels villous with long straightish hairs
                                  17 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.
                                       19 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
                                       19 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
                                16 Petals 4-9 (-11) mm long, yellow, without red lines in the throat.
                                         20 Stems repent, rooting at most nodes; seeds brown, transverse ridges not white; stipules oblong with distinct flanges and free auricles
                                         20 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.
                                           21 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
                                           21 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
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