T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Cardamine hirsute (Hairy Bittercress)

Kingdom: Plantae
(Unranked): Angiosperms
(Unranked): Eudicots
(Unranked): Rosids
Order: Brassicales
Family: Brassicaceae
Genus: Cardamine
Species: C. hirsuta
Binomial name: Cardamine hirsute
Common names: Hairy bittercress, Bittercress. Bitter cress, land cress, lamb’s cress, flick weed

Cardamine hirsuta is a winter annual plant native to Europe and Asia, but also present in New Plymouth and NZ as an invasive weed.
The plant is a member of the mustard family (Brassicaceae) and is edible as a bitter herb. It has tiny white flowers from July –December. The small four-petaled white flowers are borne in a corymb on wiry green stems. These soon followed by the seeds and often continuing to flower as the first seeds ripen. The seed is borne in siliquae (narrowly elongated seed capsule) 15 – 20mm long which, as with many Brassica species, will often burst explosively when touched, sending the seeds flying far from the parent plant. 
Seeds germinate in the autumn, and the tiny plants are green throughout the winter months.
Hairy Bittercress can be very invasive. This plant grows best in damp, recently disturbed soil. These conditions are prevalent in nursery or garden centre plants, and Hairy Bittercress seeds may be introduced with those plants. Once it is established, particularly in lawn areas, it is difficult to eradicate.
This plant is cited as one of the herbs invoked in the pagan Anglo-Saxon Nine Herbs Charm, recorded in the 10th century.

A young Cardamine hirsuta.

Closeup of the young leaves

Older leaves

The sparsely hairy mature leaves of Cardamine hirsute

Cardamine hirsute's   siliquae

One of Cardamine hirsute explosive pods has just sprung open and the seeds are about to drop out.

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/