Page:Manual of the New Zealand Flora.djvu/788

748

Perennial aquatic herbs. Stems slender, simple or branched. Leaves wholly submerged and translucent, or floating and opaque, alternate or opposite, entire or toothed; stipules intrafoliar, free, or adnate to the petiole or base of the leaf. Flowers small, green, hermaphrodite, ebracteate, sessile in a dense spike on an axillary peduncle arising from a membranous spathe. Perianth-segments 4, small, herbaceous, concave, valvate. Stamens 4, inserted at the base of the segments; anthers sessile, 2-celled, extrorse. Carpels 4, sessile, distinct, 1-celled; stigma oblique, decurrent; ovules solitary, aflixed to the inner angle of the cell, campylotropous. Ripe carpels or drupelets 4, small, coriaceous or spongy, ovoid or subglobose, obtuse or beaked by the recurved persistent stigma, 1-seeded. Seed curved, reniform; testa membranous; embryo with a large radicle and narrow incurved cotyledon.

1. P. natans, ''Linn. Sp. Plant.'' 126.—Stems creeping below, long or short, simple or sparingly branched, terete. Floating leaves on long petioles; lamina 2–4 in. long, oblong or elliptic or elliptic-lanceolate, acute or subacute, subcordate and shortly biplicate at the base, coriaceous, 20–30-nerved with copious cross-veins and