23. Ivesia aperta (J. T. Howell) Munz, Suppl. Calif. Fl. 111. 1968.
Potentilla aperta J. T. Howell, Leafl. W. Bot. 9: 239. 1962
Plants greenish gray to silvery; glands sparse. Stems decumbent to erect, 1.5–4.5 dm. Basal leaves (7–)10–20(–23) cm; sheathing base densely strigose abaxially; stipules absent; petiole 4–8 cm, hairs abundant, ascending, ± 1(–3) mm; leaflets 20–35 per side, loosely overlapping, 3–15(–20) mm, lobes 0–4(–5), oblanceolate to elliptic, hairs abundant, ascending to appressed, ± 1(–2) mm. Cauline leaves 3–8. Inflorescences (10–)20–250-flowered, 1–14 cm diam., flowers arranged in several to many tight glomerules of 5–20 flowers. Pedicels 1–3(–15) mm. Flowers 5–12 mm diam.; epicalyx bractlets lanceolate, 1.5–2.5(–3.5) mm; hypanthium cupulate, 1–2 × 2.5–4(–5) mm, 1/2–2/3 as deep as wide; sepals green, 2.5–4(–5.5) mm, acute to acuminate; petals light yellow, oblanceolate to broadly obovate, 2–7 mm; stamens 20, filaments filiform, 1–4 mm, anthers yellow, 0.4–0.6 mm; carpels 2–7, styles 2–4 mm. Achenes brown, 2–3 mm.
Varieties 2 (2 in the flora): w United States.
Many historic collections of Ivesia aperta were identified as I. pickeringii. D. D. Keck (1938) considered I. aperta to be no more than a yellow-flowered form of I. sericoleuca, a situation clarified and rectified by J. T. Howell (1962). The ranges of the two species overlap in Sierra Valley, California, with mixed populations occurring near Beckwourth and in the valleys north of Sierra Valley. In general, var. aperta occurs in the southeastern portions of the valley and I. sericoleuca occurs on the western side; the species are not otherwise sympatric. In addition to petal color, which fades in herbarium material, I. aperta differs from I. sericoleuca in having smaller flowers with shallower hypanthia. Hairs at the base of the stems and petioles of I. aperta are relatively short (to 2 mm) and generally ascending; those of I. sericoleuca are longer (to 4 mm) and spreading. Variety canina combines the petal color of var. aperta and floral dimensions of I. sericoleuca.
