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Oxalis
See list of 7 species in this genusThe caulescent, yellow-flowered species of Oxalis have a confusing taxonomic history due to misapplication of names in past works (see species discussions for further details). Further, hybridization has been noted between some species in North America (e.g., between O. corniculata and O. dillenii, between O. dillenii and O. florida). References: Eiten (1963), Nesom (2009b).
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1a. Plants lacking leafy, aerial stems, the petioles and peduncles arising directly from rhizomes or a bulbous base; corolla largely or entirely white or pink-purple to purple, 10–20 mm long
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2a. Inflorescence consisting of a solitary, peduncled flower; petals white with pink veins (rarely pink-purple throughout) [Fig. 756]; sepals without a callus tip; leaves and peduncles arising from slender rhizomes
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2b. Inflorescence an umbel with (1–) 2–12 (–18) flowers; petals pink-purple to purple (rarely pink or white); sepals with a pair of orange tubercles at the apex (these confluent and appearing as 1 tubercle in O. violacea); leaves and peduncles arising from one or more bulbs
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3a. Leaflets obcordate to obreniform, (5–) 8–15 (–20) mm long, with two marginal oxalate deposits, appearing as small dots on on each side of the base of the apical leaflet notch; plants usually arising from a single bulb, the bulb scales 3-nerved
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3b. Leaflets obtriangular to broad-obtriangular, 20–50 mm long, lacking marginal oxalate deposits; plants usually arising from a cluster of bulbs (rarely a single bulb), the bulb scales (3–) 5- to 7-nerved
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1b. Plants with leafy stems, the petioles and peduncles arising from nodes on the stem; petals yellow, 4–10 mm long
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4a. Plants uniformly and moderately to densely pubescent with short, appressed hairs (i.e., strigose) on the stems, branches, peduncles, and pedicels (rarely some hairs ascending); seeds brown with gray to white lines on the transverse ridges
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4b. Plants glabrous or sparsely to densely pubescent with appressed, spreading, and/or retrorse hairs, if uniformly strigose then only on peduncles and pedicels; seeds brown or rarely with gray to white lines on the transverse ridges
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5b. Stipules present, though small and inconspicuous [Fig. 755, L]; pubescence of the stem without septa [Fig. 755, L]; stems either clustered from a crown or taproot or solitary, without horizontal stems or with above-ground horizontal stems (i.e., stolons); cymes with 1–3 (–6) flowers; primary root usually thicker than stem
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6a. Stems trailing and rooting at the nodes; stipules relatively well developed (though still small), with distinct margins, rectangular; capsule commonly retrosely pubescent throughout, sometimes with intermixed, spreading septate hairs (varying to glabrous)
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6b. Stems erect to decumbent, but not rooting at the nodes; stipules very reduced, without distinct margins, appearing as a small, semicircular swelling in the axil of the petiole; capsule glabrous or sparsely pubescent apically or along ridges with appressed hairs, lacking septate hairs
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Each photo represents one species in this genus.