This little annual with ephemeral qualities, is a recent introduction from the Antipodes. Usually brought to the garden in the compost of plants and it is a nuisance weed in polytunnels - so it is important as a precaution against bringing it to your garden, to remove the surface compost of new plants which could be harbouring seed. The leaves are very similar to those of Hairy Bittercress, but are usually a brighter green in colour, often they are missing - probably because they have been eaten by slugs. The whole plant remains very flat except for the mature seed pods which stand about 3 to 4 cm high.
The roots are relatively tenacious and because of the ground-hugging nature of the plants, they are difficult to grip and uproot.
The single, white flowers are borne on upright stems which arise from the centre of the basal rosette of leaves and carry a leaf about halfway up their length. They should have four petals, but sometimes there appears to be three or even two as they are fused together. Later the long upright, pointed seed pods arise in groups of two to four at the top of the stem - they have the same explosive properties of the other Bittercresses when they mature.
It is important to remove any plants as soon as possible as they flower and mature to seed in a few weeks. Soon a flowerbed can have a covering mat of tiny plants. Weedkillers to use:-
A residual herbicide should prevent germination on paths.
If some plants have cast their seed, keep a lookout for new seedlings and treat as soon as they appear. Once established this Bittercress will spread over the whole garden if it is allowed to produce seed.

Follow these links for further details on Weeds, Weed Removal and Weed Prevention.