19. Potentilla L. (cinquefoil)

Plants annual, biennial, or perennial herbs (shrubs elsewhere) with taproots, woody rootstocks, or rhizomes. Stems variously erect or ascending to arched or spreading, in a few species stoloniferous and rooting at the tips and some of the nodes, unarmed, glabrous or hairy. Leaves alternate and sometimes also basal, sometimes appearing in clusters on short shoots, long-petiolate to sessile, the petioles glabrous to densely hairy. Stipules of various size, herbaceous, fused to the petiole but free in the terminal half, sometimes lobed or toothed, glabrous or hairy, green, in perennials those of the basal leaves usually persisting as withered scalelike remains. Leaf blades pinnately or palmately compound with 5–11 leaflets or trifoliate, the leaflets variously shaped, sessile or short-stalked, the margins usually toothed or lobed, the surfaces variously glabrous or hairy. Inflorescences terminal or axillary, clusters, panicles, or solitary flowers, the branch points often with small bracts, these usually shed early. Flowers short- to long-stalked, perigynous, the hypanthium saucer-shaped to cup-shaped or rarely disc-shaped, with a nectar disc, usually hairy, each flower with 5 bractlets alternating with the sepals (the calyx thus appearing 10-parted), these occasionally becoming enlarged at fruiting. Sepals 5, similar in size and shape, ascending to spreading, variously shaped, usually hairy, occasionally becoming enlarged at fruiting. Petals 5, more or less obovate, yellow or less commonly pale yellow, cream-colored, or white (red or purple elsewhere). Stamens 5 to numerous, the anthers yellow. Pistils 10 to numerous, densely covering the surface of the obconic or columnar receptacle. Ovary superior, glabrous, with 1 locule, with 1 ovule. Style 1 per pistil, attached terminally or nearly so on the ovary, usually jointed at the base and shed as the fruits mature, the stigma slender or somewhat club-shaped, sometimes somewhat curved. Fruits achenes, densely aggregated on the surface of the hemispheric to somewhat elongate receptacle, asymmetrically ovate in outline, glabrous or nearly so (hairy elsewhere), with 1 seed. About 400 species, North America, South America, Asia south to Australia.

Potentilla is a taxonomically difficult genus, with relatively widespread polyploidy, hybridization, and apomixis. In recent years, phylogenetic analysis of the fragarioid Rosaceae has tended to support a relatively restricted circumscription of Potentilla, with various species groups segregated generically, those with representatives in North America as Comarum L., Dasiphora Raf., Drymocallis, and Sibbaldiopsis Rydb. (Kurtto and Eriksson, 2003; Ertter 2007). For the Missouri flora, this affects only Drymocallis arguta, which is treated under that genus.

Potentilla contains a number of species that are cultivated as ornamentals. Some species also have minor, historical, medicinal uses.