Purple milk-vetch

The weather has once again been decidedly irritating. Rain was forecast, so Pete cancelled a planned trip to Wicken Fen. Of course, the sun shone all morning, but by that time he thought it was too late for him to re-arrange the trip. Instead we went into town to buy him some smart clothes for Alex's presentation and Chris's graduation in July. Usually he hates shopping, but we actually did rather well and managed to find everything we needed without too much bother.

When we arrived home he found an e-mail saying that the traps at Wicken hadn't been emptied, so he ended up going off to do that, just in time for the predicted rain to arrive. I made a short visit to Southorpe Paddock, to do my initial walkover survey. This is a small nature reserve on the limestone which has a section of Ermine Street running through it. The banks of the roman road have a very rich limestone flora with lots of rock-rose and dropwort, as well as several patches of purple milk-vetch.

Purple Milk-vetch Astragalus danicus is so named because it was thought to increase the milk yield of livestock. It's locally abundant in the British Isles, mainly growing on calcareous soils. In southern and eastern England populations are confined to chalk and limestone in the Cotswolds, Salisbury Plain, the Chilterns and the Breckland region of East Anglia. Like many British calcicoles it appears to be physically rather than chemically restricted and is equally happy growing on moderately acid sands/gravels (e.g. dunes) as long as competition from other species is low. It grows best at low altitudes in short calcareous grassland on lime-rich soils.

It is a Vulnerable Red Data List species added to the list of UK Biodiversity Action Plan priority species in 2007; not previously listed as threatened, although it has probably been declining since at least the start of enclosure in the 18th century. In 1860 the Cambridgeshire botanist Charles Babington noted that 'until recently (within 60 years) most of the chalk district was open and covered with a beautiful coating of turf, profusely decorated with Anemone Pulsatilla [pasque flower], Astragalus Hypoglottis [purple milk-vetch], and other interesting plants. It is now converted into arable land, and its peculiar plants mostly confined to small waste spots by road-sides, pits, and the very few banks which are too steep for the plough' (Babington 1860). It appears to have declined substantially on the chalk in S. England and limestone in N.E. England since then, largely due to agricultural improvement or lack of grazing.

Both these species once occurred at Southorpe Paddock, but it's been a long time now since anyone saw the pasque flower. However, the Wildlife Trust has introduced a regular regime of autumn and winter grazing, which really seems to have benefited the milk-vetch and many other low-growing species.