Floral Structure, Anther Development, and Pollen Dispersal of Halophytum ameghinoi (Halophytaceae)

A developmental and anatomical study of the staminate flowers of Halophytum ameghinoi showed decussate tepal estivation; residual growth of the receptacle after stamen inception; monocotyledonous and basic types of anther wall development; secretory, binucleate tapetal cells; tetrahedral tetrads; and binucleate pollen grains. A vacuolate stage in the archesporial cells, the structure of endothecial thickenings, and a mechanism of anther dehiscence by connective contraction are new autapomorphies for this family. Anemophily is confirmed (Plantago-type syndrome), and field studies of pollen release showed a subtle mechanism involving rigid anther wall structure, versatile anther insertion, and abaxial subterminal pores. In air currents, while anthers flutter with pores directed upwind, pollen is extracted presumably by a cavitation effect of the hooded anther tip. In a phylogenetic context, anemophily of Halophytum is of isolated occurrence within Caryophyllales, and uniovulate ovaries in sister clades probably represent a prerequisite for evolution of anemophily.