ABSTRACT
The external morphology of pollen grains in seven species of Carduus occurring in Kenya was investigated using a light and a scanning electron microscope. The grains are echinate, radially symmetrical, isopolar, spheroidal and tricolporate with lolongate ora. Pollen size, the sub-apical structure of the spines in Carduus kikuyorum R.E. Fries and the interspinal distance in Carduus keniensis R.E. Fries appear to be taxonomically valuable among the pollen characters investigated. C. kikuyorum R.E. Fries and Carduus nyassanus (S. Moore) R.E. Fries are clearly distinguished on the basis of their pollen sizes and structure of the spine apices. All other pollen features investigated are invariable or intergrade between the species.
