Pilea rivularis Wedd.

Perennial herb with prostrate and ascending stems, up to 1 m. high; apparently mostly dioecious, or at least each shoot unisexual.. Stems little branched, often ± lignified at base, glabrous, with linear cystoliths and occasionally reddish or orange glands in epidermis.. Leaves of a pair subequal or equal; stipules large and prominent, persistent, circular, oblong or ovate, 6–10 mm. long, 4–8 mm. wide, transparent, with subcordate base and rounded apex; petiole extremely variable, 0.4–5(–8.5) cm. long, glabrous or with a few hairs at connection with lamina; lamina ovate to lanceolate, 0.5–8(–10.5) cm. long, 0.5–3.5(–6) cm. wide, base cuneate to truncate or subcordate, margin crenulate to serrate, with 4–15(–20) teeth on each side, apex acute to long acuminate; lateral nerves 3–4 pairs, basal pair reaching ± 2/3 of the way to the apex before joining with the upper lateral nerves and arching towards the midnerve; both upper and lower surface with dense linear cystoliths, on the nerves of the lower surface often a ± dense indumentum of spreading hairs.. Inflorescences sessile, dense glomerules, up to 1(–1.3) cm. in diameter, mostly unisexual, rarely with a few flowers of the opposite sex intermixed, single in the upper leaf-axils, with small linear bracts between the flowers.. Male flowers 3-merous, on pedicels l–2.5(–4) mm. long; perianth globular to ovoid, ± 2 mm. long (not including appendages); tepals equal, with prominent linear cystoliths in epidermis, each with a subapical filiform appendage 0.8–1.5 mm. long.. Female flowers on pedicels 1–2 mm. long; perianth 1–1.5 mm. long, divided almost to the base, with 3 ovate, subequal lobes, the middle one with a subapical appendage up to 0.5 mm. long, lateral lobes 2/3–4/5 as long as the middle lobe, usually also with a ± developed subapical appendage; staminodal scales about as long as perianth-segments.. Achene brown to pale brown or whitish, ovoid, 1.5–2.5 mm. long, 1–1.5 mm. wide, ovoid, compressed, occasionally with a flat, marginal wing (rarely the wing dissolved into hooked bristles).. Fig. 8/F–J.