Sex Ratios ofRiccia frostiiAust. in Khartoum Province, Sudan

Abstract

Spore dispersal of the dioecious liverwort, Riccia frostii Aust., in Khartoum Province Sudan, is by the Blue Nile in flood. Although a 1 : 1 sex ratio is to be expected, sample counts have shown that females always outnumber males and the actual ratio varies from site to site. Shading has been shown to suppress the development of male thalli, while a pattern analysis and covariance analysis of an apparently homogeneous site showed that male and female thalli reacted differently to microtopographical/substrate differences on the Nile bank. Extreme age of the population produces a change in sex ratio through the earlier death of male thalli; a quickly drying substrate also produces a differential mortality of male thalli. The effect of the high summer temperatures on the dormant spores which remain in situ on the Nile banks is not known but may produce a change in the sex ratio through the differential mortality of the spores.