Myriophyllum papillosum

Perennial aquatic or marsh herb, robust; stems 30–40 cm tall, mostly 5–6 mm diam., papillose, rooting at nodes in fully emergent plants. Leaves dimorphic; submerged leaves in whorls of 4–6, broadly ovate to orbicular, mostly 15–45 mm long, pectinate, with 17–23 pinnae; emergent leaves in whorls of 4–6, linear, mostly 15–45 mm long, sometimes papillose at base, margins with 12–18 teeth on distal three-quarters. Bracteoles of male flowers oblong, 0.6–0.8 mm long, fimbriate; bracteoles of female flowers minute; flowers solitary or in fascicles of 2 or 3. Male flowers sessile; sepals 4, lanceolate, c. 0.6 mm long; petals 4, 2.5–3.6 mm long, white-hyaline, caducous; stamens 8. Female flowers shortly pedicellate; sepals and petals absent; ovary 4-celled, styles more or less sessile, stigmas reddish-purple. Fruit cubiform, green to reddish-purple; mericarps narrowly ovoid, 0.8–1.0 mm long, apex oblique, dorsal surface coarsely papillose. Flowers Sep.–Apr.