The infructescence of the poorly known Ammocharis herrei F.M. Leight. is similar to that which is diagnostic for Cybistetes longifolia (L.) Milne-Redh. Schweick. In the absence of distinct morphological differences A. herrei is placed into synonymy under C. longifolia. Plants of the amplified C. longifolia have fewer, large seeds in Namaqualand and the Richtersveld and smaller, more numerous seeds in the Western Cape. This pattern is postulated to reflect divergent strategies of resource allocation in different habitats. It is suggested that the infructescence of C. longifolia. a highly derived structure suited to tumbling, evolved from the unspecialised condition in Ammocharis as an adaptation to the high winds of southwestern Africa.