2. Thysanocarpus curvipes Hooker, Fl. Bor.-Amer. 1: 69, plate 18, fig. A. 1830.
Thysanocarpus amplectens Greene; T. curvipes var. cognatus Jepson; T. curvipes var. elegans (Fischer & C. A. Meyer) B. L. Robinson; T. curvipes var. emarginatus (Greene) Jepson; T. curvipes var. eradiatus Jepson; T. curvipes var. involutus Greene; T. curvipes var. longistylus Jepson; T. curvipes subsp. madocarpus Piper; T. curvipes var. pulchellus (Fischer & C. A. Meyer) Greene; T. emarginatus Greene; T. filipes Greene; T. foliosus A. Heller; T. hirtellus Greene; T. laciniatus Nuttall var. emarginatus (Greene) Jepson; T. pulchellus Fischer & C. A. Meyer; T. trichocarpus Rydberg
Stems 1-6(-8) dm. Basal leaves: blade oblanceolate to obovate, 1-6(-13) cm, margins subentire to sinuate-dentate, surfaces often hirsute, sometimes glabrous, (trichomes white, 0.3-0.6 mm). Cauline leaves: blade lanceolate, widest at base, base auriculate-clasping, auricles extending around stem (at least some leaves). Racemes: internodes 3-6(-9) mm in fruit. Fruiting pedicels smoothly recurved, (proximal) 3-7(-12) mm. Fruits flat or plano-convex, obovate to nearly orbicular, [3-6(-9) mm wide]; valves pubescent or glabrous, trichomes clavate and 0.2-0.4 mm, or pointed and ± 0.2 mm; wing entire, perforate, or incised, rays absent or distinct, (0-)0.2-0.5 mm wide.
Flowering Feb-Jun. Rocky slopes, washes, oak woodlands, streamsides, meadows, sometimes serpentine soils; 150-2000 m; B.C.; Ariz., Calif., Colo., Idaho, Nev., N.Mex., Oreg., Utah, Wash.; Mexico (Baja California, Sonora).
Thysanocarpus curvipes is the most widespread and variable species in the genus. Variants have been named as varieties or species, but they grade into each other imperceptibly. Notable among these are var. elegans, a form with incised or perforate fruit wings, and var. eradiatus, a form with rayless, entire wings. Some of these may be the result of hybridization with other taxa. For instance, var. elegans has large fruits and occurs in the vicinity of T. radians, the largest-fruited member of the genus. Furthermore, fruits of var. elegans often have pointed hairs like those usually found on fruits of T. radians; such hairs are not found on fruits of any other members of the genus. Thysanocarpus curvipes includes both diploid and tetraploid populations (M. D. Windham, unpubl.), but these do not appear to segregate into recognizable groups. Although the variation in T. curvipes is considerable, its great complexity prevents recognition of infraspecific taxa at this time.