Scientific name: Rorippa nasturtium-aquaticum (L.) Hayek
Common name: Water-cress
Description
Habit: A hairless perennial, to 1 m high.
Stems: Trailing to ascending or floating when in water, branched but weak.
Leaves: Alternate, pinnate, with oval leaflets.
Flowers: White, actinomorphic, 6 mm across, in racemes; sepals 4, free, 1-1.5 mm; petals 4, free, 1-1.5 mm; stamens dehiscing inwardly; ovary superior.
Fruits: A silique, cylindrical, oblong, 18-25 x 3-4 mm, with a long, often stout style; the seeds numerous, arranged in 2 rows in the fruit, covered with a network of indentations with less than 12 depressions across the width.
Rorippa x sterilis, a hybrid between Rorippa microphylla and R. nasturtium-aquaticum, is commonly found with the two parent species and occasionally in absence of either. The fruits of R. x sterilis have at most, 3 well-formed seeds in each fruit, the remainder of the fruit sterile.
Habitat: Marshes, ditches, streamsides, pools, turloughs.
Distribution: Occasional on limestone, rare elsewhere.
Native status: Native
Of conservation interest: No