18. Sibbaldiopsis Rydberg, Monogr. N. Amer. Potentilleae. 187, plate 100, figs. 6–10. 1898.
[Genus Sibbaldia and Greek –opsis, resembling]
Barbara Ertter, James L. Reveal
Potentilla Linnaeus subg. Sibbaldiopsis (Rydberg) B. Boivin; Potentilla sect. Tridentatae (Th. Wolf) Dikshit & Panigrahi
Subshrubs to suffrutescent herbs, perennial, often ± matted, 0.2–3 dm, sparsely to moderately strigose to pilose; stoloniferous and rhizomatous (caudex diffusely branched). Stems 1–10+, ascending to erect, ˂reddish˃. Leaves persistent, basal and proximally cauline [or evenly cauline], alternate, ternate; stipules persistent, basally adnate to petiole, sheathing, ovate, margins entire; petiole present; blade ± obovate [or broadly cordate] in outline, (0.5–)1–3(–4) cm, leathery, leaflets 3, oblanceolate to narrowly oblong, margins nearly flat to ± revolute, shallowly 3(–5)-toothed apically, venation pinnate, abaxial surface sparsely to moderately strigose to pilose, adaxial glabrous or sparsely strigose or pilose, rarely densely so. Inflorescences terminal, [1–]3–20-flowered, cymose, flat-topped; bracts present, reduced [or leafy]; bracteoles absent. Pedicels present, ˂± straight˃. Flowers 10–20[–30] mm diam.; epicalyx bractlets 5; hypanthium patelliform, 0.5–1.5[–2] × 3–5 mm, villous; sepals 5, spreading, broadly ovate; petals 5, white, sometimes pink-tinged [or yellow], elliptic-obovate [to orbiculate], ˂longer than sepals˃; stamens 20(–30), shorter than petals, ˂filaments filiform, not flattened, glabrous, anthers with theca horseshoe-shaped, rimming narrow to broad connective, dehiscing by a continuous, narrow, marginal slit˃; torus ± hemispheric; carpels 20–50, hairy, styles attached proximal to middle of achene to sub-basal, ˂filiform˃; ovule 1. Fruits aggregated achenes, individually deciduous, obliquely ovoid, 1.2–1.5 mm, villous; hypanthium persistent; sepals persistent, erect; styles tardily deciduous, ˂jointed˃. x = 7.
Species 3 (1 in the flora): e North America, Asia.
Rydberg based Sibbaldiopsis solely on the North American S. tridentata, which T. Wolf (1908) placed in his Grex Tridentatae with the Himalayan Potentilla ambigua Cambessèdes (not Gaudin) and P. miyabei Makino of Hokkaido and the Kurile Islands. Both Asian species have leafier stems and inflorescence bracts than the type species, as well as fewer flowers with broader yellow (versus white) petals. The treatment presented here provisionally follows that by J. Soják (2004, 2008, 2009b) with the inclusion of all three species in Sibbaldiopsis, using S. cuneifolia (Bertoloni) Soják and S. miyabei (Makino) Soják for the Asian species. More recently, however, J. Paule and J. Soják (2009) have proposed to include Sibbaldiopsis in Sibbaldia, since the species are intermingled in molecular phylogenies. Whether S. tridentata itself can be retained in a distinct monospecific genus remains to be determined.
SELECTED REFERENCE Paule, J. and J. Soják. 2009. Taxonomic comments on the genus Sibbaldiopsis Rydberg (Rosaceae). Čas. Nár. Muz., Rada Přír. 178(4): 15–16.