Cytogenetic studies in the genus Tribolium (Poaceae: Danthonieae). II. A report on embryo sac development, with special reference to the occurrence of apomixis in diploid specimens

The genus Tribolium Desv. forms part of the tribe Danthonieae and is endemic to southern Africa. This genus comprises twelve species and is subdivided into three sections, namely Tribolium, Acutiflorae and Uniolae. This is the first study on embryo sac development in this genus. The ovaries are monolocular with a single anatropous ovule. The nucellus is uniseriate and is protected by a multicellular integument. Polygonum-type embryo sac development is present in all species. Additional to the development of reduced embryo sacs, unreduced embryo sac development of the Hieracium-type has been observed in diploid specimens of T. echinatum (Thunb.) Desv., T. uniolae (L. f.) Renv. and T. utriculosum (Nees) Renv