Oilseed rape, Brassica napus

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Brassicacae usually have four separate sepals and four separate petals. There are usually 6 stamens: 4 longer inner stamens and 2 outer shorter stamens, although the latter are sometimes lost. The ovary is usually two-celled, though each cell may contain many ovules in some species. A single style bears two stigmas.

Capsella bursa-pastoris, the Shepherd's Purse.

Above and below: The characteristic 'purse-shaped' fruit capsule which gives the Shepherd's Purse its common name. Some forms of this species are diploid ( with two sets of 8 chromosomes each, 2n = 16) whereas others are tetraploid (4n = 32). The diploids tend to have smaller fruit and more dissected and more acutely tipped leaves.

This type of short pod which consists of two fused carpels (length less than three times the width) found in brassicas is called a silicle or silicula.The silicula is a type of capsule: a dry dehiscent fruit formed from a syncarpous gynoecium (fused carpels), the individual carpels of which open. The plural of silicula is siliculae.

Below: Stellate hairs on the pedicels.

Valves of Shepherd's Purse

Shepherd's Purse membrane

Above: each fruit dehisces by shedding two valves, releasing the orange-brown seeds. The dividing membrane (septum or replum), to which the two valves were joined, remains, outlined by veins. This is characteristic of siliques and siliculae. The protuberances projecting from the rim veins are the placentas, as can be seen below, in which some of the seeds are still in situ with attached placentas.

Shepherd's Purse seeds and placentae


Garlic Mustard, Alliaria petiolata

Garlic mustard

Alliaria produces long upright pods (more than three times as long as wide) called siliques (singular = silique or siliquae, singular = siliqua). Each silique contains from 6 to 22 seeds and plants may produce from 1 to 150 or so siliques (larger plants may produce up to five flowering stems). The siliqua and  The flowers are visited by hoverflies, midges and bees and are self-compatible. The seeds are probably dispersed by animals. There is no vegetative/clonal reproduction. The seeds induce sneezing. The inflorescence is a raceme (a central axis bearing equally spaced flowers borne on short stalks with the oldest flowers at the base) and forms at the end of the main stem and at the ends of branches.

Garlic Mustard

The above ground parts smell and taste of garlic when crushed. The leaves have been used in salads and have a higher concentration of vitamin C than oranges and a higher vitamin A content than spinach (per unit mass). The plant is usually biennial or a winter annual, but can be perennial. It produces a slender taproot (which may be branched) and overwinters as a rosette. The rounded or deltoid leaves are strongly cordate at the base (incurved like a heart icon) and the leaf margins are crenate or toothed.

Garlic Mustard

Alliaria petiolata is also called Garlic Hedge Mustard and Jack-by-the-Hedge as it is commonly found in hedgebanks and also in open spaces within woods and roadsides by woods. it was formerly used as a salad herb due to its strong flavour and was hence called 'Sauce Alone'.


Lepidium draba, Hoary Cress / Whitetop / Whitlow Pepperwort

Pepperwort

The genus Lepidium (Pepperworts) includes the Garden Cress (Lepidium sativum) with its peppery taste. Lepidium draba is a perennial mustard. Upon germinating it rapidly develops a long vertical taproot which puts out lateral roots. Eventually the roots may reach a depth of 3 to 5 m and horizontal roots may reach 4 m in length. Both the taproot and the lateral roots may bear (adventitious) buds that can give rise to subterranean rhizomes and vertical shoots above ground. These buds and rhizomes are an important mechanism for vegetative (clonal) reproduction in this plant. Short root fragments, a few cm long, can also rapidly regenerate into new plants. The main stem reaches 10 - 80 cm tall and the cauline (stem) leaves are alternate and undivided (simple) with two prominent basal lobes or auricles that wrap around the stem. The radical leaves 9rosette leaves, born on the rootstock)

Pepperwort

Pepperwort

The flowers have 6 stamens and 4 white petals.The petals are more than twice the length of the sepals. The inflorescence is a corymb (the outer flowers are borne on longer pedicels so that all the flowers are brought to the same horizontal level, more-or-less).

Pepperwort

The heart-shaped (deltoid) capsules of Lepidium draba are siliculae.The shape of the fruit and whether or not they have wings and beaks / prominent style remnants enables the different species of Lepidium to be most easily distinguished. In Lepidium draba, the style is more than half the length of the pod and the fruit has no wing. The fruit is more convex on the lower surface. One valve is usually significantly larger than the other with the seeds in the smaller valve being abortive. The valves are deeply constricted in the middle (where they meet the replum) such that they carry the seeds with them when they fall.

The seeds are myxogenic, meaning they secrete a slime capsule when moistened, by means of secretory myxogenic or mucilaginous cells. The benefits of such slime in those seeds that secrete it are various. Such slime enables the seed to imbibe trace amounts of water, such as morning dew in dry habitats and it has been demonstrated that this water can be used to repair and hence maintain the embryo's DNA and so enhances survival and germination in dry or salty habitats. The slime can also facilitate attachment to soil and perhaps to animals for dispersal and may enhance survival of a seed in an animal's digestive tract, enhancing dispersal.

Pepperwort

These Pepperwort specimens were photographed in the British Isles where they grew on waste ground in Kent, on somewhat sandy soil not far from the coast. They are typically found in waste places, fields, along railways and on sandy soil near the coast. They are not native to Britain but were first introduced to certain sea ports, including Swansea, around 1802 (it has been suggested that they probably arrived in ship's ballast). A major introduction occured in 1809 when troops returned from the 1809 Walcheren campaign in the Netherlands where they were brought inside hay-filled mattresses for wounded soldiers. A farmer on the Isle of Thanet ploughed the mattresses into a field and the plant slowly spread from there and is now found throughout Britain. Lepidium draba is sometimes called 'Thanet Cress'.

L. draba is native to southwest and central Asia and Mediterranean and Black Sea coasts. it spread to the rest of Europe perhaps about 300 years ago and naturalized. It has since spread further and is now naturalized on every continent except Antarctica. It is particularly invasive in western North America.


Further Reading

A well-researched review on Lepidium draba:

https://www.gardenorganic.org.uk/sites/www.gardenorganic.org.uk/files/organic-weeds/cardaria-draba.pdf