STUDIES ON POLLEN MORPHOLOGY OF ROSACEAE

Light and scanning electron microscope studies of pollen representing genera from all tribes of the Rosaceae reveal a variety of form and sc ulpturing. Ail genera examined produce radially symmetric isopolar mon ads. Most genera in subfamilies Maloideae, Prunoideae, and Spiraeoidea e produce tricolporate striate grains with large perforations in valle ys between ridges. These tectate perforate grains have a chambered por e covered by arching ektexinal pore flaps. The ridge-and-valley patter n can vary from 1 - long ridges parallel to the colpus, to 2 - medium to long ridges looping near the poles, to 3 - shot weaving and crossin g ridges. Striate perforate pollen occurs in tribes Dryadeae, Kerrieae , Roseae (operculate) and Rubeae of subfamily Rosoideae. in some Rubus species perforate and verrucate sculpturing occurs. Tribe Potentillea e (= Fragarieae) produces pollen with microperforations rather than ty pical perforations and most genera have an operculum. Coluria, Fallugi a, Geum, Orthurus, and Waldsteinia of Dryadeae produce striate micro-p erforate pollen, suggesting that they may belong in the Potentilleae. Filipendula (Ulmarieae) is prominently verrucate. Tuberculate perforat e sculpturing occurs in Cercocarpus, Cowania, and Purshia suggesting a natural group distinct from the rest of the family. The diverse Poter ieae (= Sanguisorbeae) has mainly tricolporate and some hexacolporate (Sanguisorba) grains all with an operculum. Some genera (Agrimonia gro up) have striate pollen, but most have microverrucae and perforations. Within the tribe, a distinctive group of mainly south hemispheric gen era (Acaena, Cliffortia, Cowania, Hagenia, Leucosidea, Margyricarpus, Polylepis, Tetraglochin) has tricolporate perforate pollen, often with a short colpus, sculpturing of macroverrucae and rugulae covered by m icioverrucae. These pollen characteristics suggest a distinct evolutio nary lineage.