Potentilla rivalis Nutt.
CC = 4
CW = -3
MOC = 16
Family - Rosaceae
Habit - Taprooted annual or biennial forb.
Stem - Loosely ascending from a spreading base, to 60 cm, moderately to densely pubescent with longer, straight, spreading to loosely appressed hairs and shorter, crinkly hairs.
Leaves - Alternate. Leaf petioles to 6 cm long, hairy. Upper leaves usually sessile. Stipules 5-15 mm long, narrowly ovate to ovate, sharply pointed at the tip, the margins entire or toothed and often hairy, the surfaces hairy. Leaf blades 2-6 cm long, palmately compound or the largest leaves sometimes with a short rachis, with 3 or 5 leaflets, these 0.5-6.0 cm long (the central or terminal leaflet the largest), oblanceolate to obovate or oval, rounded to bluntly pointed at the tips, the margins coarsely toothed or scalloped, the upper surface green, glabrous or sparsely to moderately hairy, the undersurface lighter green, moderately hairy.
Inflorescences - Terminal panicles, sometimes reduced to racemes, mostly with numerous flowers.
Flowers - Bractlets 3-6 mm long, narrowly elliptic, moderately hairy. Hypanthia 4-5 mm in diameter, shallowly cup-shaped. Sepals 3-7 mm long, broadly ovate, sharply pointed at the tips. Petals 1.5-3.0 mm long, about half the length of the sepals, oblanceolate to obovate, yellow to pale yellow. Stamens usually 10. Ovaries with the styles attached near the tips.
Fruits - Achenes 0.7-0.9 mm long, the surface smooth or occasionally slightly wrinkled, brown, unwinged.
Flowering - May - October.
Habitat - Streambanks, openings of bottomland forests and swamps, pastures, open disturbed areas.
Origin - Native to the U.S.
Lookalikes - Broadly, other species of Potentilla.
Other info. - This species of cinquefoil is relatively uncommon in Missouri, with most reporting counties being adjacent to the large rivers. Missouri lies near the far eastern edge of the plant's range, which extends westward to the Pacific Coast and into Canada and Mexico. The plant is reasonably easy to identify by its large numbers of small yellow flowers. These have the morphology characteristic of Potentilla, with 5 bractlets closely subtending, and alternating with, the 5 sepals. The petals are only half the length of the sepals, so are not usually visible in lateral view. The plant tends to prefer moist areas.
Photographs taken at San Pedro Riparian National Conservation Area, Cochise County, AZ, 5-27-2016 (SRTurner).