Dragon Trees and Mother-in-Law's Tongues

The inflorescences and flowers of many species are very similar. The basic unit of the inflorescence is a raceme, with fascicles of flowers being borne at nodes. Pedicels are articulated, and exude apparently nectariferous secretions towards the base. The flowers are usually white, less often pale yellow, pale pink or light green with a narrow tube and open nocturnally by recurvature of the corolla lobes. This colour and morphology, with their often heavy scent, suggests moths are the primary pollination vector. Significant exceptions are Sansevieria sambiranensis, which has coral-pink to red bracts and flowers, bee-pollinated Dracaena draco and its allies, where the tube is very short or absent, and the taxa from Hawaii related to Dracaena aurea which have yellow, bird-pollinated flowers. The main differences are said to lie in the pollen and fruit morphology. There has been limited sampling of the former, but what material has been studied suggests that there is monosulcate, reticulate pollen in Dracaena, as is prevalent in monocots, but that in Sansevieria is operculate (Ojeda et al. 1984, Ojeda & Ludlow-Wiechers 1995). The fruit in Dracaena is a berry, with a distinct exocarp and an apical scar or persistent style base (Bos 1984). Sansevieria is said to possess a sarcotesta, with no apical style base or scar and gymnospermous seed development (Nakai 1936, and several subsequent authors). Despite this, they are similar in overall appearance and probably dispersed by birds, which may help to explain their widespread distribution and frequent occurrence on isolated islands. Other characters which have been suggested to differ between the two genera are the point of filament insertion in the corolla tube, thickening of the filament, the degree to which the stigma is lobed and seed morphology (Mwachala 2005) appear less convincing.