Stigma Morphology in Commelinaceae

The stigmas of all species examined in the Commelinaceae are papillate and the majority trifid or triangular. In species of Callisia, Tripogandra and Zebrina, the unpollinated stigma surface is of the ‘dry’ type but in the genera Aneilema and Commelina some species possess ‘wet’ surfaces, others ‘dry’ In most other species secretion increases following flower opening and these are regarded as ‘wet’ Almost all pollinated surfaces are ‘wet’, secretion often inundating stigmas and occasionally being accompanied by papilla collapse. There is also considerable diversity in gross stigma size, and in the number, distribution, size, shape and cellular composition of papillae. In Coleotrype natalensis, Cyanotis species and Siderasis fuscata a fringe of papillae is present around the neck of the open stylar canal whereas in all other species the number and size of papillae are large enough to cover the opening. Papillae have been classified into seven categories based on shape. Categories A (Aploleia, Callisia), F (Commelina) and G (Cyanotis) are genera specific, category D specific to the Tradescantia fluminensis group, the remaining categories occurring in several diverse genera Papilla shape and cellular composition is particularly variable in stigmas of species in Gibasis and Tradescantia. An additional feature of the surface ornamentaion is the incidence of a sparse covering of raised ‘blisters’ of variable size. These are absent only from Callisia, Cyanotis, Aneilema and Commelina species. Species in the latter two genera have papillae covered by a distinctive folded cuticle. These results are discussed in relation to function and taxonomy.