ORBICULES IN ANGIOSPERMS - MORPHOLOGY, FUNCTION, DISTRIBUTION, AND RELATION WITH TAPETUM TYPES

Orbicules, or Ubisch bodies, are sporopollenin particles lining the in ner tangential and sometimes also the radial tapetal cell walls, They occur only in species with a secretory tapetum, The surface ornamentat ion of orbicules and pollen of the same species is often strikingly si milar. Although orbicules were discovered more than a century ago, the se structures remain enigmatic since their function is still obscure. Proposed hypotheses about their possible function are discussed. We al so deal here with topics such as the possible allergenicity of orbicul es and their representation in the fossil record. The use of orbicule characters for systematics is reviewed. The distribution of orbicules throughout the angiosperms, based on a literature review from the firs t report until today, is shown in a list with 314 species from 72 fami lies. Those species found in the literature without orbicules are pres ented together with their tapetum type. We plotted this information on a dahlgrenogram to visualize the distribution of orbicules. Orbicules occur in all subclasses of the angiosperms, Their occurrence is not c orrelated with certain modes of pollination or habitats.