Flora of New Zealand Series

Infl. of 1–2–(3) male fls, maturing one after the other, and one female fl., the whole enclosed within or associated with a membr. spathe. ♂ of a single stamen; filament projecting well beyond spathe; pollen sacs 1–2, rounded, splitting transversely; pollen globular. ♀ of rounded ovary and short erect style; carpel single, ovules 1–6, basal. Fr. flattened, sts ± winged. Seeds relatively large, smooth or ribbed with operculum at micropilar end. Very small aquatic herbs floating on or just under the surface of still or slowly moving water, often together forming a complete cover. Lvs absent, the plant consisting of ± flattened, green platelets with or without roots, each platelet arising from a bud in a horizontal pouch on an older platelet; infl. produced in a similar pouch. Genera 4, widespread in temperate and tropical countries.

The plants, known as duckweeds, are small; individuals are rarely as long as 5 mm., and the minute fls are not often seen. N.Z. spp. have been described and figured (Mason, Post-primary School Bull. 4, 1950, 237). The treatment followed here is that of Daubs (Monograph of the Lemnaceae, Ph.D. Thesis, Univ. Illinois, 1962, also in Illin. Biol. Monographs No. 34, 1965, 1–118).

Fig. 10. LEMNACEAE. Spirodela oligorrhiza : plants viewed from side and from below, × 5. Lemna minor : plants viewed from side and from above, the latter showing two stamens projecting from a lateral flowering pouch, × 5. Wolffia arrhiza : plants viewed from side, showing vegetative bud emerging from pouch at end; also from above, the older platelet showing central flowering cavity, × 10. © All rights reserved. [Image: 4X21]