Oxalis stricta
Oxalis pilosa
common yellow oxalis, common yellow wood sorrel, European wood-sorrel, upright yellow oxalis, upright yellow wood-sorrel, yellow woodsorrel
hairy western wood-sorrel, hairy wood sorrel
1(–3) from base, erect or later leaning or falling over and decumbent, not rooting at nodes, 20–60(–90) cm, herbaceous, villous, hairs ± straight, spreading, usually nonseptate and septate, septate hairs commonly concentrated at nodes, very rarely only nonseptate.
usually 2–8 from base, decumbent to ascending, 10–40 cm, becoming woody proximally, sparsely to densely pilose, hairs spreading irregularly to ± deflexed, nonseptate, longer hairs 0.6–1.2 mm.
basal and cauline;
stipules rudimentary;
petiole 2–8 cm, hairs septate and nonseptate;
leaflets 3, light green to yellowish green, obcordate, (8–)10–20(–30) mm, lobed 1/5–1/3 length, surfaces glabrous, oxalate deposits absent.
basal and cauline;
stipules oblong, margins narrowly flanged, apical auricles absent;
petiole (1–)2–6 cm, hairs nonseptate;
leaflets 3, glaucous and gray-green to yellowish green, obcordate, 5–12 mm, lobed 1/5–1/3 length, surfaces glabrous to loosely strigose to hirsute-villous, oxalate deposits absent.
usually regular cymes, rarely irregular cymes, (1–)5–7(–15)-flowered;
peduncles 3–9(–11) cm.
umbelliform cymes, 1–2(–3)-flowered;
peduncles 1.5–5 cm.
homostylous or slightly to strongly heterostylous, usually within or slightly above level of leaves;
sepal apices without tubercles;
petals yellow, without red lines, (6–)8–11 mm.
semihomostylous or distylous, within level of leaves;
sepal apices without tubercles, surfaces strigose to hirsute-strigose;
petals yellow, rarely with red lines proximally, 8–12 mm.
± cylindric, nearly terete, abruptly tapering to apex, 8–15 mm, villous to puberulent or glabrate, hairs septate.
angular-cylindric, abruptly tapering to apex, 12–17(–20) mm, strigose-hirsute.
brown, transverse ridges rarely white.
brown to blackish brown, transverse ridges rarely with whitish lines or spots.
= 18, 24.
Oxalis stricta
Oxalis pilosa
Oxalis stricta is uncommon and probably adventive in Canada and the western United States. The species is recognized by the combination of its tall (rarely up to nearly a meter), erect stems from a short, simple rhizome; septate hairs; cymose inflorescence; and small flowers. Septate hairs on the stems and petioles are easily recognized (lens) by their colored cross-walls, but they vary greatly in density. In villicaulis forms, the hairs are dense and evenly distributed, but in most plants over the range they are localized around the nodes and intermixed with nonseptate hairs. Often they are sparse; rarely they appear to be absent on plants with greatly reduced vestiture overall.
A. Lourteig (1979) identified this species as Oxalis fontana, typified by a plant from northern China, and applied the name O. stricta to the species identified by G. Eiten (1955, 1963) and here as O. dillenii. The basis for the difference lies in selection of lectotypes. Choice of stricta as the correct epithet acknowledges that the description of O. stricta by Linnaeus best matches these plants and that selection of a Morison illustration as lectotype characterizes the species long-naturalized and weedy in Europe and probably known first-hand by Linnaeus. C. E. Jarvis (2007) has confirmed this choice of lectotype. Oxalis dillenii is appropriately lectotypified by a John Clayton collection from Virginia. The situation has been summarized well by D. B. Ward (2004).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Oxalis pilosa has been treated as an infraspecific entity within O. albicans, but the two are sympatric in the southwestern United States and although each is variable, there appear to be relatively few unequivocal intermediates. Reports of O. pilosa from Texas apparently were based on misidentifications of O. albicans and perhaps also of O. dillenii.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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