Cardamine hirsuta L.
Cardamine hirsuta L. var. reniformis J.M. Black
Brassicaceae
bitter cress, common bitter cress, common bitter-cress, common bittercress, flick weed, flickweed, hairy bitter cress, hairy bittercress, hairy wood cress, hairy wood-cress, hairy woodcress, hoary bitter cress, hoary bittercress, Pennsylvania bittercress, popping cress, wavy bitter cress
Native to Africa, Europe and southern Asia.
Primarily naturalised in the Moreton district in south-eastern Queensland, and rarely naturalised in other parts of the state.
Widely naturalised in southern Australia (i.e. in eastern New South Wales, the ACT, Victoria, Tasmania, in many parts of South Australia and in south-western Western Australia). Also naturalised in the southern parts of the Northern Territory and on several offshore island territories (i.e. Lord Howe Island, Norfolk Island and Christmas Island).
A weed of parks, footpaths, lawn, gardens, plant nurseries, pot plants, glasshouses, disturbed sites and waste areas. It is particularly common in damp shady sites.
A small, short-lived (i.e. annual), herbaceous plant forming a rosette of leaves followed by slender upright (i.e. erect) stems 10-35 cm tall.
Several green or purplish coloured stems are usually produced from the base of the plant, and these stems are usually unbranched. These slender stems are usually hairy (i.e. hirsute) towards the base of the plant, but are usually hairless (i.e. glabrous) towards the top of the plant.
The leaves form a distinct basal rosette at the base of the plant and are alternately arranged along the stems. These leaves (2.5-10 cm long) are once-compound (i.e. pinnate) and borne on stalks (i.e. petioles) 5-50 mm long. They have 2-7 pairs of leaflets and end in a single larger (i.e. terminal) leaflet. The leaflets (4-20 mm long and 6-30 mm wide) are egg-shaped in outline (i.e. obovate) to somewhat rounded (i.e. orbicular) with lobed or bluntly-toothed (i.e. crenate) margins and rounded tips (i.e. obtuse apices). The leaves on the highest parts of the stem are relatively few, and are usually much smaller with narrower (i.e. oblanceolate or linear) leaflets. They are shortly stalked (i.e. shortly petiolate) or almost stalkless (i.e. sub-sessile). All the leaves are green with a sparse covering of hairs on their upper surfaces and leaf stalks (i.e. they are sparsely hirsute).
The small white flowers are arranged in elongating clusters (5-15 cm long) at the tips of the branches (i.e. in terminal racemes). They are densely arranged at first, but the clusters elongate as the flowers open and the fruit begin to mature. Each flower has four tiny green, pinkish or purplish sepals (1-2.5 mm long and 0.3-0.7 mm wide) and four white or pink-tinged petals (2-4.5 mm long and 0.5-1.1 mm wide), and is borne on a stalk (i.e. pedicel) 4-14 mm long. The flowers also have four (rarely five or six) stamens and an ovary topped with a style and stigma. Flowering occurs mostly during winter or spring.
The long and narrow (i.e. linear) fruit resemble small pods (i.e. they are siliquae) and tend to be borne upright (i.e. erect) on upwards arching stalks (i.e. ascending pedicels). These cylindrical fruit (10-25 mm long and 0.7-1.5 mm wide) are hairless (i.e. glabrous) or sparsely hairy (i.e. hirsute) and have two compartments separated by a partition (i.e. false septum). They turn from green or purplish-tinged to pale yellowish-green as they mature and eventually split open, explosively releasing the numerous small seeds. These seeds are light brown to reddish-brown in colour and flattened and narrowly winged (0.9-1.3 mm long and 0.6-0.9 mm wide).
This species reproduces by seed, which are spread small distances when they are explosively released from the mature fruit. Seeds may also be spread by water and in contaminated soil (e.g. in pot plants).
This species is not currently declared under any state or local government legislation in the region.
As this species is not a declared plant in Queensland, its control is not required. It is usually not a problem in natural vegetation, but should be controlled if it invades sensitive bushland and conservation areas.
For information on the management of this species see Suburban Weeds (Third Edition), by Kleinschmidt, Holland and Simpson (1996), page 35.
Common bittercress (Cardamine hirsuta) is very similar to flickweed (Cardamine flexuosa), but these two species can be distinguished from each other by the following differences:
Common bittercress (Cardamine hirsuta) is also similar to some closely related, and relatively uncommon, native species (i.e. Cardamine paucijuga and Rorippa spp.). However, these native plants are usually hairless (i.e. glabrous).
Common bittercress (Cardamine hirsuta) is primarily a weed of gardens, lawns, glasshouses and pot plants in south-eastern Queensland, and is troublesome to the nursery industry. It occasionally also invades natural vegetation, where it is generally found growing in moist shaded habitats. For example, in a muddy creek-bed near Eumundi, on a shaded sandy creekbank beside the South Pine River, in disturbed open forest in Brookfield, in seepage areas in the Moggill Ferry Reserve, and in a heavily grazed eucalypt woodland near Beenleigh.
This species is sometimes regarded as a minor environmental weed in south-eastern Australia (i.e. in the wider Sydney and Blue Mountains region and in some parts of Victoria).