XVI International Botanical Congess

The small chromosome clade of Pelargonium exhibits a remarkable diversity of growth forms, ranging from shrubs, stem succulents and geophytes to herbaceous annuals. Phylogenetic analyses suggest that some anatomical traits correlated with stem architecture, e.g. stem succulence, have arisen multiple times. Anatomical and developmental investigations of stem structure show clade-specific patterns in the degree of cambial activity responsible for stem thickening and in the types of cells produced by the cambium. When similar stem architectures arise in different clades, they may be achieved via different anatomical and developmental modes, again illustrating the great diversity present within the genus.