STUDIES ON ONONIS IN BRITAIN 



1. Hyhridity in the Durham Coast Colonies of Ononis , 

 By J. K. Morton, Ph.D. 



Department of Botany, University College of the Gold Coast 



The two common species of Ononis in the British Isles, O. repens L. and O. spinosah., 

 are normally readily distinguishable. Plants with apparently intermediate characters 

 have occasionally been reported, but in most localities the species are quite distinct and 

 usually grow in different habitats. Such, however, is not the case on the Durham coast, 

 where both species intermingle on the Magnesian Limestone cliffs, and where the identity 

 of many individuals is indeterminate. The present paper is concerned with assessing the 

 degree to which the characters of these two species overlap in this region and determining 

 whether this is due primarily to hybridity or to intraspecific variation. O. repens in 

 Britain has a diploid chromosome number of 64, and O. spinosa of 32. The existence of 

 hybrid plants with an intermediate chromosome number has recently been established 

 in these Durham coast colonies. Further work on the cytology of these, and other, plants 

 is in progress and a report on this will appear in due course. 



Location of the Colonies 



Two colonies were studied on the Durham coast; one in the north, at Marsden, 

 and the other in the south, at the Blackball Rocks. These two colonies are isolated from 

 each other, being separated by many miles of cliff on which only normal O. repens 

 occurs, and also by the large area of low-lying land at the mouth of the River Wear. 

 The Marsden colony is considerably smaller than the Blackball Rocks colony and is 

 confined to a narrow belt of land, only a few feet wide, at the top of the Magnesian 

 Limestone cliffs. The cliffs here differ from those at the Blackball Rocks in not having 

 a well-developed grassy slope at the top. For the most part they fall sheer, almost from 

 the top, and hence the area in which these plants can grow is very narrow, being limited 

 at the back by the cliff path, behind which is cultivated and waste land. At the Blackball 

 Rocks there are broad, steep, grassy slopes above the cliffs, and on these Ononis grows 

 in profusion. The enormous number of individuals in this colony made it impossible to 

 examine them all. The position of the colony, also, on a steep slope over the cliffs, made 

 it difficult to use random sampling methods. These slopes are, however, divided into a 

 series of hollows, and in one of these every plant of Ononis was examined and scored. 

 At Marsden, the smaller size of the colony made it possible to examine and score every 

 plant (with the exception of a few on inaccessible cliff ledges) growing on the cliffs from 

 the miners' cottages at the south end of the bay to the promontory at the north end. 



For purposes of comparison, pure colonies of both O. repens and O. spinosa, growing 

 in other localities, have been scored by the same methods as the Durham coast colonies. 

 Pure colonies of O. repens, on the coast at Whitburn, and of O. spinosa, in the Quarrington 

 Hill area, were selected because of their close proximity to the mixed colonies at Marsden 

 and Blackball Rocks. Two other colonies, from much further afield, were also studied - 

 the O. spinosa colony from the coast on the east side of Eastbourne, Sussex, and the 

 O. repens colony from nearby on Beachy Head. 



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