Anisantha madritensis

Anisantha madritensis (L.) Nevski (Poaceae)

Bromus madritensis L.

Compact brome, Pawrwellt Dwysedig

Status in Britain: VULNERABLE.

Status in Europe: Not threatened.

A. madritensis is a grass of dry open habitats, occurring mainly in man-made sites including wall-tops, old buildings, open waste ground, roadsides and cracks in pavements. It occurs in a few semi-natural sites, such as in the Avon Gorge, where it grows on limestone outcrops, stony slopes and open grassland on warm freely draining calcareous soils. Associated species are varied, as the grass grows as an intrusive species in the gaps in many communities. In the Avon Gorge, the most frequent associates are Centranthus ruber and Crepis vesicaria, but in its most natural sites, the associates are Bromus hordeaceus, Catapodium rigidum, Geranium robertianum, Hornungia petraea, Saxifraga tridactylites and Sedum acre.

This is an annual species, flowering from May to July. It is tetraploid and may have arisen from the hybridisation of A. sterilis and A. rubens. There is some evidence of good seed longevity and germination being triggered by disturbance and light (Lovatt 1982). Hot dry summers may reduce competitors, allow light to the seed-bank, with larger populations of A. madritensis the following year.

In the Avon Gorge, where it was first recorded by Lightfoot in 1773, it is often regarded as a native (e.g. Ryves, et al. 1996). There it grows on screes and on unstable limestone rock ledges, which regularly provide newly disturbed ground into which the plant can seed. The population is large, and several tens of thousands of plants may occur in good years. It has also recently been reported at a second site nearby at Shirehampton (S.Parker, pers. comm.). Another possibly native site is in Pembrokeshire, where it grows in limestone grassland and on rocky outcrops near Castle Carew. It is probably also native on the Channel Islands. Otherwise, A. madritensis is generally regarded as an alien, though an old and well-established one. For instance, it grows on ancient city-walls in Exeter, and has been known in Southampton since 1806. The plant is scattered throughout southern England, with a few locations in northern Britain and in southern Ireland. It appears to be under no special threat. Urban colonies persist despite herbicides, tarmac, re-turfing, and the cleaning of buildings.

This species has its stronghold in southern Europe, where it is often a common weed, but its range extends eastwards to northern France, and to North Africa, south-west Asia and Macaronesia. It also is found in Afghanistan, on Atlantic Islands, and is now naturalised in Australia and North America.

D. A. Pearman, R. M. Walls and M. J. Wigginton