Flora of New Zealand Series

Characters of the family. Spp. probably c. 10, of which 2 are known in N.Z.

Taxonomic criteria within the genus are discussed by Mason (N.Z. J. Bot. 5, 1967, 519–531). She recognises 2 N.Z. spp., both of which have spirally coiling peduncles, and which differ morphologically and/or cytologically from the N. Hemisphere spp. hitherto erroneously recorded from this country. These new spp. can scarcely be regarded as endemic until Australian representatives have been critically reviewed. Both spp. are commonly referred to as Horse's mane weed or Lakeweed, but these terms probably include other plants of similar form.

Pollination us. occurs on the surface of the water. The 2 N.Z. spp. appear to differ in that in R. polycarpa the pollen sacs tend to break loose at dehiscence and float away while in R. megacarpa pollen sacs remain attached after pollen has escaped.

Mason (Post-primary School Bull. 4, 1950, 240) records: "In lakes the waves may roll the fruitlets, black with the outer green flesh removed, until the stalks interlock and great black balls up to a foot in diameter are formed".

Carpels can be counted most accurately at flowering; at later stages unfertilized carpels remain small and ± shrivelled and, where achenes develop unevenly, some may have dropped before the last mature.

Fig. 3. RUPPIA. R. polycarpa : inflorescence; leaf-tip; fruit showing endocarp; mature fruits from lower flower of a pair. R. megacarpa : fruit showing endocarp; leaf-tip; inflorescence. © All rights reserved. [Image: 4X2M]