common wall cress
Arabidopsis thaliana (L.) Heynh., (Arabis thaliana, Sisymbrium thalianum, Stenophragma thaliana)
Thale cress is an erect annual, rarely biennial weed, native on cultivated ground, bare places, on banks, walls, rocks, and waysides throughout Britain. It occurs sporadically as a garden weed and is frequent in poached grassland. Thale cress also occurs on roadsides and railways. In early surveys of Bedfordshire and Norfolk it was usually well distributed and was associated with light loams and sandy soils. According to some studies, it is abundant on dry, stony and usually acid soils. However, others studies suggest it is absent from acidic soils and prefers a soil pH range of 6.0 to 8.0. Thale cress does not occur on wetland.
Individual plants vary in response to the environment but populations also differ due to simple genetic mutations. The short life cycle and small growth habit have made it the ideal plant for genetic research. It is perhaps ironic that much of the GM technology that has led to the development of herbicide tolerant crops is based on the relatively simple genetics of this otherwise insignificant weed.
Thale cress flowers from April to May and again from September to October, although it may be found in flower throughout the year. Some populations require vernalisation before flowering is initiated others do not. The flowers are automatically self-pollinated but can be cross-pollinated. Plants have been known to produce seeds just 4 weeks after emergence. Seed pods contain an average of 33 seeds. The average seed number per plant is 2,739.
Light quality during seed development can influence the level of seed dormancy. Plants grown under a higher ratio of red to far red light produce non-dormant seed. In the field, light and nitrate levels are limiting factors for field germination of some strains of thale cress but others are indifferent to light. Germination levels are much lower under a canopy of leaves. Some forms of thale cress are short-day plants others do not respond to daylength. In the UK, thale cress may appear to behave as a winter annual but winter and summer races are thought to occur.
Field emergence in cultivated soil extends from February to December but most seedlings emerge in peaks in March-April and September-November. Seed that germinates in late September-October forms a leaf rosette by November. Flower buds develop in January-February, the flower stem elongates in March, and the flowers open in early April. Seeds are then dispersed in early May. The majority of fresh seeds are dormant but during burial, both fresh and older dormant seeds after-ripen. At first seeds will germinate only at low temperatures, then at gradually increasing temperatures. During the autumn and winter, seeds lose the ability to germinate at high then at low temperatures and then become dormant. Seed germination increases after a period of dry storage.
Thale cress forms a persistent soil seedbank.
Thale cress is not considered a serious arable weed and where it occurs may be controlled by hoeing and surface cultivation.
Updated October 2007.