Trifolium ochroleucon

Trifolium ochroleucon Hudson

Sulphur clover

Status: scarce

This clover is usually found on the chalky boulder clay, less commonly on chalk, in the lowlands. Most records are from roadside verges or old trackways, less commonly from old pastures and railway embankments and cuttings. As it rarely exceeds 50 centimetres in height it cannot withstand competition from tall grasses such as Calamagrostis epigejos and Festuca arundinacea. It is thus usually associated with shorter mesophytic grasses including Anthoxanthum odoratum, Briza media, Festuca rubra, Helictotrichon pubescens, Lolium perenne, Trisetum flavescens and the sedge Carex flacca. These occur with T. ochroleucon on verges mown in high summer, less commonly in lightly grazed pasture. 

Associated species such as Cirsium acaule, Filipendula vulgaris, Pimpinella saxifraga, Plantago media, Primula veris and Sanguisorba minor indicate calcareous soil, while Betonica officinalis, Lysimachia nummularium, Pulicaria dysenterica, Silaum silaus and Valeriana officinalis suggest seasonally wet soil. Melampyrum cristatum and Pimpinella major are characteristic associates on wood-borders in East Anglia.

T. ochroleucon is a long-lived caespitose perennial. Little is known about its reproductive biology, but it has obviously colonised habitats such as railway cuttings from seed. Many of its old roadside localities have been destroyed in the re-alignment and widening of roads, the use of verges for public utilities such as telephone cables, and the fashion of manicuring verges near farms and villages in the interests of tidiness. T. ochroleucon in England occurs in a predominantly arable landscape, and the relatively few old pastures not ploughed up have usually received dressings of phosphate (as basic slag) and nitrogenous spring dressings which favour the palatable grasses Lolium perenne and Dactylis glomerata at the expense of plants of low competitive ability. Verges left uncut soon develop into tall (1.8 metres) stands of Festuca arundinacea and other coarse grasses: their mattress of dead leaves allows few associates to survive.

T. ochroleucon is fairly widespread in western, southern and central Europe, predominantly on clay soils. It extends eastwards to Iran and is also recorded from North Africa.

D. E. Coombe