Flora of New Zealand Series

Kariba weed

Aquatic fern forming dense floating mats with lvs often tightly overlapping. Floating lvs elliptic to broadly elliptic, entire, folded, to 2.5 × 2 cm, light or brownish green, becoming somewhat darker on margins, densely covered on upper surface in papillae bearing groups of 2 or 4 uniseriate hairs united at their distal ends. Papillae to 3 mm long. Sporocarps in long straight secund chains, hairy, c. 1 mm diam., containing mostly empty sporangia.

N.: N. Auckland (frequent throughout, particularly near the coast), Auckland (Western Springs Lake and Rangitoto Id), S. Auckland (Hamilton, Matamata, Hauraki Plains).

Widespread in tropics and subtropics 1964

Lakes, ponds and dams with still or slow-moving water, swamps.

N.Z. material (Plate 2) has been variously referred to as S. natans (L.) All., S. herzogii Sota and S. auriculata Aublet, but is almost certainly S. molesta, described by Mitchell (loc. cit.) from Lake Kariba where it is a rampant weed. It is sterile and possibly of hybrid origin. According to Mitchell, it can only be distinguished from S. auriculata, S. biloba Raddi and S. herzogii by its small ♂ sporocarps bearing empty sporangia.