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10 May 2020

Blooming gorgeous: purple milk-vetch

Written by Ciaran Hatsell , Ranger, St Abb’s Head NNR
A close-up of little purple-flowering plants growing close to the ground in a grassy area.
Purple milk-vetch is one of the rare plants to be found at St Abb’s Head.
Purple milk-vetch is a plant that adds a dash of purple to the floral painting here on the wildflower meadows of St Abb’s Head NNR.

Purple milk-vetch (Astragalus danicus) begins to flower in June and July, coinciding with the peak period for several butterfly species, for which it’s an important food plant. It also provides a great nectar source for a wide range of other insects, including many bee species. Its common name comes from the fact that it used to be believed that cows who ate this plant yielded more milk!

It’s a member of the pea family, many of which are able to fix nitrogen into the soil (a process where the plant is able to convert nitrogen in the air into ammonia in the soil, making it usable for plants and animals). This enables purple milk-vetch to survive on nutrient-poor soils and in places where growing is tough. Because it’s a low-growing plant, it also benefits from our grazing work here at St Abb’s Head, which keeps the competitive grass species in check and allows for many wildflower species to flourish. It’s a careful balance to provide the right habitat for this and many other plants, achieved mainly by grazing in the autumn and winter, and taking the grazing stock off in the spring.

A close-up of the small delicate flowers of purple milk-vetch, growing in the grass. The petals are long compared to the rest of the plant, and point up at the sky.
This pretty little flower is a sign of summer at St Abb’s Head.

Purple milk-vetch is listed as Endangered by the IUCN due to a decline caused by chemical fertilisers in the 20th century. Many plants in the UK are similarly under threat from human activities, including intensification of agriculture, use of pesticides and industrial development. However, although purple milk-vetch may be scarce in most parts of the UK, in some areas at St Abb’s Head that’s hard to believe!

Next time you visit St Abb’s Head in the summer, keep an eye out for this subtle but splendid plant among the other rock stars like thrift; it really does play a very important role in the ecosystem.

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