Rapistrum Explained

Rapistrum, the bastard cabbages, is a genus of the family Brassicaceae with a distinctive cross like arrangement of its petals. It is also known^[1] as wild-turnip or turnipweed. Species of Rapistrum are annual to perennials (Lifespan from 1 to 2 or more years). The yellow petals are accompanied by sepals that stand vertically at near right angles (erecto-patent). Leaf shape and arrangement varies from rough toothed (dentate) to a configuration of opposingly lobed pairs along the plant stalk, pinnately lobed.

Etymology

The word "Rapistrum" is formed from the Latin rapa ("turnip") and -astrum, ("incomplete resemblance").^[2]

Fruit

The genus Rapistrum has a characteristic fruit comprising two segments, one distal and one proximal:

• The distal (upper division) is the part of the fruit farthest away from the point of attachment. The distal is endowed with a ribbed spheroid base (globose) that tapers to form a narrowed projection. It holds a single seed.
• The proximal (lower division) is the part of the fruit nearest to the point of attachment. Possesses a more uniform narrower shape compared to the distal above, giving the fruit a waist. It holds a maximum of three seeds, more commonly none or one.

The fruit varies between species in the genus. The distal of R. rugosum is strongly ribbed and narrows to form a beak whereas R. perenne is comparatively less wrinkled and ends with a style that stubbornly resists detachment, 'a persistent style'.

When ripe the distal breaks away in an across-wise fashion, breaking transversely.

Bibliography

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Notes and References

1. Web site: Rapistrum . 2024-09-12 . Flora North America.
2. Web site: Warwick . Suzanne I. . Rapistrum . Flora North America.