Flora of New Zealand Series

Purple-backed Duckweed

Fig. 15B

Platelets to 5 × 3 mm, elliptic-obovate, ± inflated, slightly asymmetric; dorsal surface green, flat to convex; ventral surface convex, usually strong red-purple; nerves obscure. Roots 2-5. Spathe open along one side. Fruit ovoid, 1-seeded. Seed ribbed, reticulate; operculum prominent.

N. From Auckland southwards. S. Marlborough - between Wairau and Awatere Rivers; Canterbury. Ch. Still, fertile waters.

(India, China, S.E. Asia, Polynesia, Australia)

First record: Lancaster 1930: 563, as S. oligorrhiza.

First collection: "Palmerston North, pond off Waldegrave Rd", V.D. Zotov, 18.4.1929 (CHR 11997).

FL. 11-12- (3). FT. 1-3.

Formerly known in N.Z. as S. oligorrhiza (Kurz) Hegelm., but den Hartog and van der Plas (Blumea 18, 1970, 360) showed that S. punctata, based on Lemna punctata G. Meyer 1818 has priority over S. oligorrhiza based on L. oligorrhiza Kurz 1866.

We treat S. punctata as adventive on the grounds that it is a conspicuous plant of its type, being larger than Lemna and having a distinctive purple underside. It is unlikely to have been missed by earlier collectors.