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Brassica
rapa (L.) Janchen Quick
Links: 1.1 Appearance: An annual to biennial plant with bright yellow flowers and growing upto 1 m in height. Is distinct from most brassicas by its clasping stem leaves and from Oilseed rape by the frequent presence of rosettes, coarse hairs on the leaves and smaller, darker petals. 1.2 Ecology: Occurs as a native plant growing on riverbanks in England and Wales (Waterside B. rapa) and probably as an introduced species growing as an arable weed (Weedy B. rapa) and in disturbed habitats (Ruderal B. rapa), such as roadside verges, construction sites, tips and gardens. The native plant requires winter chilling in order to flower, whereas the introduced weed flowers without chilling. 1.3 Life Histories: The waterside B. rapa usually grows as a winter annual or biennial, flowering from April to late June. The seeds will germinate throughout the year and the plants will commonly overwinter in rosette form. The weedy B. rapa grows as a strict annual. It flowers in early spring (between February and May) and the seeds germinate in the autumn. The life history of ruderal B. rapa is unknown. 2. Ease of Hybridization with Oilseed Rape Brassica rapa is self incompatible and artificial hybrids are easily made with B. napus, with upto 93% of the crosses setting seed. The triploid hybrid looks similar to B. napus and can only be accurately identified by cytological and molecular examination. The hybrid has much reduced fertility, though it does set some seed, and later generations are frequently more fertile. Riverbank populations occur in England and Wales south of the Cheviot Hills. As a weed, B. rapa occurs rarely, but is scattered throughout the UK and is most abundant in North-East England and Eastern Scotland. Populations growing in disturbed land occur sporadically throughout the UK, but probably have a tendancy to become extinct within a few years. Science
Paper: "Hybridization Between Brassica
napus and B. rapa on a National Scale in the United Kingdom".
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