Two of the three subspecies are frequently found in Herefordshire, a slightly unusual situation, subspecies segetalis and subspecies nigra. They are sometimes tricky to name, but much more commonly partition well on the basis of their general appearance and habitat preferences.
Subspecies segetalis is a tall scrambler common throughout Britain. It reaches a metre but is commonly half a metre, supporting itself in tall vegetation with its tendrils. Its flowers are usually paired and have the standard paler than the keel. It is NEVER a component of traditionally managed, longstanding species-rich grassland, perhaps because continuity of cover by perennial plants has never allowed it, as an annual, to get a hold in the root zone and establish a meaningful seedbank. If found there it is a sure-fire indicator of recent disturbance.
Pic 1: typical segetalis. Tall, paired flowers (one of the upper ones has withered) with keel darker than standard, broad oval leaflets, well-developed tendrils, pushing up through rank vegetation.
Subspecies nigra is generally a small plant of short grassland flowering low down in the sward and not really needing much in the way of tendrils, getting support instead from its procumbent habit, resting against the open grasses and other herbs with which it grows. Its flowers may be paired in larger plants but more often seem to be borne singly with us, and are a brilliant uniform pink, like jewels in the grass. Unlike ssp segetalis, it is usually a component of at least half-decent grassland.
Pic 2: typical nigra: Low, single flowers with keel and standard the same colour, growing low down in managed pasture. This subspecies likes open, warm, free-draining sandy substrates and in most of Britain is restricted to coastal sands. However, in Herefordshire it is quite widespread throughout, apparently exploiting the sandstone and siltstone elements of the Old Red Sandstone and the soils they give rise to. The droughty and open nature of these soils explains why this subspecies, also an annual, has always been able to make a home here by exploiting the gappiness within the grassland.
Pic 3: nigra again. The conspicuously narrower leaflets in this taxon visible bottom R give rise to the useful English name narrow-leaved vetch. Poland & Clements give a 4mm cut-off for the two subspecies, but in VC36 the leaflets are often much narrower than this.
Pic 4: Both subspecies together, to show not atypical size differences, nigra (L) and segetalis (R). The abrupt change in leaflet shape in nigra basal to upper leaves (termed heterophylly) can be seen well, though this is often not as clear-cut as some keys would have you believe. Both from Vowchurch Common, the nigra from the middle of a patch of old acid hill pasture, the segetalis from the gappy hedge bank round the outside.
Pic 5: detail of a shoot of ssp nigra on gravel, showing the heterophylly, with lower leaves on the R
Pic 6: As pic 4, but with a taller specimen of nigra added to the picture on the L. Although this has twin flowers and the plant is larger, the narrow leaflet shape and uniform flower colour is maintained
The third subspecies, sativa, also occurs in Herefordshire, but only as a rare casual. It is now included in some bee and winter birdseed cereal margin mixes sown within agri-environment schemes, so may increase. Note in the pic below that it has the same two-coloured flowers as segetalis. Only record this subspecies though if the plant strikes you as HUGE and if you are in the correct habitat, or if you are late enough in the year to see the ripe pods, usually hairy and pale yellowish brown, rather than hairless and black/dark.
Pic 7: subspecies sativa (L) alongside spent subspecies segetalis (R) to show size comparison. Note the black pods of segetalis. Cereal margin at Canon Pyon, Herefordshire.
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