Flora of New Zealand Series

watercress

Perennial stoloniferous herb. Stems trailing, glabrous, to several m long. Lvs glabrous, all similar, but becoming smaller near infl., pinnate, petiolate, 2-10-(25) × 1-5 cm; basal auricles small; leaflets rounded, ovate; margins entire or sinuate. Pedicels glabrous, slender, erecto-patent, spreading to deflexed at fruiting, (5)-10-15-(18) mm long (very rarely to 30 mm). Sepals 1.5-2.5 × 0.7-1.5 mm. Petals white, (3)-4-6 × (1)-1.5-2.5 mm. Silique glabrous, narrow-oblong, curved, (8)-12-15-(18) × 2-2.5 mm; valves with distinct midrib, at least below; style c. 1 mm long. Seeds distinctly in 2 rows per locule, brown, c. 1 mm long, coarsely reticulate with 20-50 polygonal depressions per face.

N.; S.; Ch.: throughout but commonest in N.

Eurasia, N. Africa 1852

Streams, ditches and drains.

R. nasturtium-aquaticum is very similar to R. microphylla, but differs in its seed surface and also tends to have smaller fls, shorter pedicels and broader siliques. The sp. is often treated in the genus Nasturtium as N. officinale R. Br. It has also been referred to in N.Z. as Radicula nasturtium-aquaticum.

The hybrid R. microphylla × R. nasturtium-aquaticum has been recorded from N.Z. It is intermediate between the parents and sets few or no seeds.