Myriophyllum alpinum

Perennial aquatic herb, glabrous; stems 10–50 cm long, 1–2 mm diam., tangled, rooting at lower nodes. Leaves in whorls of 3 or 4; submerged leaves ovate to orbicular, c. 5–10(–15) mm long, pectinate, with 6–9 pinnae; emergent leaves similar or pinnae reduced to long teeth. Bracteoles ovate, 0.5–0.7 mm long. Male flowers more or less sessile, solitary; sepals 4, triangular to ovate, 0.4–0.5 mm long; petals 4, 2.9–3.5 mm long, red to yellow, persistent; stamens 8. Female flowers sessile, solitary; sepals and petals absent; ovary 4-celled, styles linear, becoming reflexed, stigmas white. Fruit cubiform, reddish-purple; mericarps ovoid, 0.8–0.9 mm long, truncate, smooth or sparsely papillose. Flowers late spring–summer.