Pollen types in the Amaranthaceae - Morphology and evolutionary significance

The Amaranthaceae is a family within the order Caryophyllales and comprises approx. 800 species in about 70 genera. A representative selection of 130 species from 67 genera was studied. The pollen was found to be generally pantoporate. High resolution scanning electron microscopy and additional light microscopy revealed many new characters of the apertures, in particular of the ektexinous bodies on the aperture membrane, of the exine microsculpture, of the wall ultrastructure, and information on pollenkitt. The subsequent analysis of the resulting large data set led to the recognition of 17 well defined pollen types. The taxonomic distribution of pollen characters in the Amaranthaceae indicates that pollen morphology is informative at different taxonomic levels. Certain pollen characters can be used to circumscribe genera or groups of genera, and often also to distinguish species. Unique within the angiosperms are the hook-shaped, stellately arranged ektexinous bodies covering the pore membranes in pollen of nine genera. Palynological data support the basic subdivision of the Amaranthaceae into the Amaranthoideae and Gomphrenoideae, but indicate that the commonly accepted tribes and subtribes in the classification of Schinz are largely polyphyletic. Pollen characters further provide evidence that a previously described pollination syndrome involving betalains as optical attractants is derived within the Amaranthaceae.