Rorippa amphibia
Common name
tall yellow cress, marsh yellow cress
Family
Brassicaceae
Flora category
Vascular – Exotic
Structural class
Herbs - Dicotyledons other than Composites
Brief description
Tall herb, up to 1 m tall, with various shaped leaves, the lowest being deeply lobed, the uppermost with no lobes, but all with toothed margins, flowers are bright-yellow c. 6 mm across in large flower heads at the top of the stem.
Distribution
Very local Northland to Waikato and Bay of Plenty.
Habitat
Swamps, margins of water bodies and cultivation weed in wet areas.
Features
Perennial rhizomatous herb. Stems erect, glabrous or finely hairy, 30-80 cm tall. Lvs ± glabrous, variable in shape, spathulate- oblanceolate, cuneate; margins toothed. Lower lvs petiolate, auriculate at base, deeply pinnatifid with lobes becoming shallower toward apex, 8-16 × 2-6-(7) cm. Upper lvs smaller, pinnatifid or toothed, sometimes linear; auricles becoming 0. Pedicels glabrous, erecto-patent to patent, sometimes deflexed at fruiting, (5)-7-10-(12) mm long. Sepals 2-3 × 1 mm. Petals bright yellow, 3-6 mm long. Silicle glabrous, elliptic to ovoid, 1.5-3-(4) × 0.6-1-(2) mm, but often not or poorly developed; valves veinless; style 1 mm long. Seeds reddish brown, c. 1 mm long, finely colliculate, in 2 rows per locule. As this plant is self-sterile many populations do not produce seed in New Zealand.
Similar taxa
Similar to the introduced creeping yellow cress (R. sylvestris) and the native poniu (R. palustris) but much taller, petals being > 2x length of the petals (unlike poniu) and fruit being oval rather than sausage shaped with peduncles > 2x the length of the fruit (unlike creeping yellow cress).
Flowering
November to February
Flower colours
Yellow
Fruiting
November to February
Life cycle
Seed and rhizomes dispersed by water or contaminated machinery.
Year naturalised
1870
Origin
Temperate Eurasia and North Africa
Reason for introduction
Unknown, seed or soil contaminant
Control techniques
Can be controlled manually, mechanically or herbicidally depending on situation.
Etymology
rorippa: A latinized form of Rorippen, a Saxon vernacular name used by Euricius Cordus
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA). Features description from Webb et al. (1988).
References and further reading
Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. (1988). Flora of New Zealand Volume 4: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch.
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Clapham, A.R.; Tutin, T.G.; Warburg, E.F. (1962). Flora of the British Isles. Cambridge University Press, Second Edition. 1269pp.