Short, White Brassicas With Round Seed Pods
What are they?
This page covers members of the brassica family that typically grow less than 50cm in height and have white - usually rather small - flowers. They all share the same general appearance of four-petalled, white flowers that are followed by short, rounded seed capsules that may be either globular, or flattened. For identification purposes, it is wise to wait until seed capsules have started to develop, as this will help to narrow your search.
Where are they found?
This is a group of only loosely related plants, so there is much variation in the habitat choices, from urban habitats to roadsides, heaths and wetlands. However, the habitat can be a valuable aid to identification for some species - especially the coastal ones, so be sure to check these details in the individual species notes below.
Identification
All these plants have white, four-petalled flowers and rounded seed pods, so you need to look elsewhere for identification clues. Most important will be details of the leaves - both basal and those on the flowering stems, while tiny differences in the flowers and the seed capsules can help with closely related species. As noted above, the habitat and location is also useful to note.
Field Penny-cress Thlaspi arvense
An ancient introduction of disturbed ground, common and widespread in arable areas, gardens and other bare ground. Flowers May to July, sometimes later. A variable plant with a compact head of tight flowers, that elongates greatly as the flattened, disc-like seed capsules appear.
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Garlic Penny-cress Mummenhoffia alliacea
(Thlaspi alliaceum) A recent introduction from Europe. A handful of records since the 1990s but remaining rare as a non-established casual in gardens. Flowers May to July, sometimes later. Flowers rarely open fully; stem leaves clasping at the base. Seed capsules differ from those of Field Penny-cress in having a much smaller 'winged' edge and in being globular rather than flattened and disk-like.
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Common Whitlowgrass Erophila verna
A native annual; common and widespread and found on all kinds of dry, open areas, including sandy soil, pavement cracks and on walls. Flowers March to May. Tiny plants that are often no more than 4-5cms tall and thus easily overlooked, but often common and forming quite extensive colonies. The tiny, white flowers have very deeply divided petals, while the basal leaves are usually covered in stiff, white hairs which extend up the basal part of the flowering stem. Note that these hairs can wear off, making identification more difficult later in the season. Seed capsules oval in outline and greatly flattened, like a deflated rugby ball. Separation from the much rarer Glabrous Whitlowgrass is very difficult; leaves have petioles 0.5-1 times as long as the leaf-blade and petals are notched more than half way to the base.
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Glabrous Whitlowgrass Erophila glabrescens
A native annual; rare in dry, open sites on sandy soil, along roadsides and even on old walls. Flowers March to May. Tiny plants that are often no more than 4-5cms tall and thus easily overlooked. Extremely similar to Common Whitlowgrass and difficult to tell from it. The whole plant is typically hairless, leaves have petioles 1.5-2.5 times as long as the leaf-blade (though beware of very young plants still developing) and petals are notched less than half way to the base.
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Early Scurvygrass Cochlearia danica
(Danish Scurvygrass) Native annual of coastal habitats in drier parts of saltmarsh and in sandy locations, including in towns. Since about the early 1980s, this species has rapidly colonised the bare edges of major roads throughout the region where salting occurs during the winter months. Often forms extensive colonies of low mounds of white or pinkish flowers along major duel carriageways. Flowers March to June. Leaves more angular, less rounded than those of other scurvygrasses; upper leaves without stalk, but not clasping the stem. Seed capsules globular, narrowed at both ends.
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English Scurvygrass Cochlearia anglica
Native biennial or short-lived perennial, quite common in coastal saltmarshes, most typically in rather wet and muddy substrates. Flowers April to July. Basal leaf blades taper into the petiole at the base. Upper leaves unstalked, clasping the stem. Seed capsules flattened oval.
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Common Scurvygrass Cochlearia officinalis
Native biennial or short-lived perennial, uncommon or rare, in drier, upper parts of coastal saltmarshes around The Wash, Breydon Water and in the south-east of our region. Flowers May to August. Despite the English name, this is the least common of the three scurvygrasses in our region. Basal leaf blades rounded at the base, upper leaves unstalked, clasping the stem. Seed capsules globular, oval, not flattened.
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Sweet Alison Lobularia maritima
Introduced from Europe. Very popular as a garden annual and occasionally self-seeding outside of gardens. Now well established in milder, coastal areas where it most often grows from walls and in dry locations. Flowers April to September. Forms low-growing mounds with flowers lasting well through the season. Leaves narrow, greyish-hairy.
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Sea Rocket Cakile maritima
An annual plant which occurs commonly right on the strandline on open, sandy or shingly beaches. Flowers June to September. A straggly plant with deeply-lobed, fleshy leaves and white or very pale pink flowers.
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Hoary Alison Berteroa incana
Introduced from Europe. Rare in our region but long established in one or two locations in the Breckland area. Flowers June to August. A slender plant, growing to 60cm but often shorter. The whole plant is covered in dense, star-shaped hairs.
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White Ball-mustard Calepina irregularis
Introduced from mainland Europe. Recorded in Cambridge as a weed of cultivation, probably having originated from imported nursery stock. Flowers May to August. Perhaps most easily confused with some of the pepperworts, or Penny-cresses, but easily told by the ball-shaped fruits on long stalks.
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Abyssinian Kale Crambe hispanica ssp. abyssinica
(Ethiopian Mustard) Introduced from East Africa as a culinary plant. Occasionally grown on allotments, from where plants were noted spreading at Sheringham, Norfolk recently. Flowers May to August. A spreading plant, to one metre in height, but often much shorter. Stems typically lightly bristly.
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