Callitriche petriei R.Mason
Type locality: Waikato River at Ngaruawahia. Type: W, D. Petrie, 4/2/1906.
Plants creeping, with ascending or erect branches 3-7 cm. high. dioec. or almost so. Lvs spathulate, thin, c. 2·2 mm. long (1·2-(6) mm.), the larger lvs often with short side veins arising from the midrib and two lateral veins. Fls solitary, us. alternately on either side of stem, ebracteate. Filaments elongating to 2-4 mm.; anthers c. 0·4 mm. wide. Styles 1·7-2·2 mm. long. Fr. broader than long, 0.6-0.75 × 0.7-0.9 mm., thicker at base than at top; commissural groove narrow and shallow; lobes rounded, not keeled, not winged; pedicel c. 0·2 mm. long.
DIST.: N., S., Ch. Wet ground at edges of streams and lakes from lat. 37° to 46° 30'. Known at present from only scattered localities, apparently absent from lat. 42° to 45°.
FL.- FT. 1-3, so far as known.
Kirk (Stud. Fl. 1899, 156) under C. muelleri adds: "Var. obtusangula. Leaves obovate, narrowed into a petiole. Fruits larger and more orbicular, with a very narrow wing.-Sp., Le Gall. ex Hegelm. Monog. Call. [1864] 54 . . . most frequent in the South."
Cheeseman (Man. N.Z. Fl. 1925, 545) under C. muelleri remarks: "There seem to be two forms of this-one with a broad wing occupying a third of the whole width of the fruit, the other with a much narrower wing. The last-mentioned form was referred by Mr. Kirk to C. obtusangula Hegelm. Monog. Callit. (1864) 54, t. 3, f. 3 : but this determination is clearly erroneous, the true obtusangula having rounded angles to the fruit, which is not at all winged." In W are two specimens collected by Berggren-(a) Bay of Is, determined as C. macropteryx; (b) Rotoaira, determined as C. obtusangula. Rotoaira specimens agree well with C. petriei R. Mason.