Systematic Placement of Dasypogonaceae Among Commelinid Monocots: Evidence from Flowers and Fruits

Despite progress in clarifying the relationships of Dasypogonaceae (four genera, Baxteria, Calectasia, Dasypogon, and Kingia), their infrafamilial relationships and precise affinities within the commelinid clade remain unsatisfactorily resolved. This paper reviews existing data on the systematic affinities of Dasypogonaceae. It also presents new data on floral structure in all four genera, and data on floral ontogeny in Dasypogon. In Dasypogon, Kingia, and Baxteria the ovary is trilocular and septal nectaries are present around the ovary base. In Calectasia, the ovary is unilocular and septal nectaries are entirely absent. Two subfamilial groupings within Dasypogonaceae (Calectasia–Dasypogon and Baxteria–Kingia) are proposed on the basis of leaf anatomy and ovule and ovary morphology. Many floral characters are plesiomorphic in Dasypogonaceae, but some morphological characters support a close relationship with the order Poales sensu lato, especially the epidermal location of the silica bodies. The unusual long-stalked “drumstick” inflorescences of Dasypogon and Kingia resemble those of some Poales, in which flowers are frequently borne on condensed inflorescences. A possible close relationship between Dasypogonaceae and some Poales such as Rapateaceae and Thurniaceae merits further exploration.