Sex-ratio variation in the gynodioecious shrub Gnidia wikstroemiana (Thymelaeaceae)

The determination of sex-ratio variation is a useful guide for identifying models of sex-ratio evolution in gynodioecious species. This study counted the numbers of female and hermaphrodite plants in five populations of the gynodioecious shrub Gnidia wikstroemiana distributed over 2.3 degrees of latitude in dry, highland shrublands and grasslands of South Africa. Population sizes ranged from 71 to 435 plants with populations occurring on diverse rocky terrains along a 422-m altitudinal gradient. Female frequencies varied from 35 to 47% but sex-ratios did not differ significantly among the five populations. However, sex-ratios in three populations occurring on ridge slopes deviated significantly from the 1:1 ratio while those populations located on the crests of mountains did not. These results suggest that both nuclear gynodioecy and subdioecy are involved in the sex-ratio evolution of this species. (C) 2009 SAAB. Published by Elsevier B.V. All rights reserved.