Anomalous secondary thickening in roots of Daviesia (Fabaceae) and its taxonomic significance

Abstract

PATE, J. S. KUO, J., DIXON, K. W. & CRISP, M. D., 1988. Anomalous secondary thickening in roots of Daviesia (Fabaceae) and its taxonomic significance. Investigations of 55 species of Daviesia show 24 to have anomalous secondary vascular development in their roots and the remainder to be of conventional root anatomy. Species showing the trait exhibit early cessation of cambial activity in the central stele of the seedling followed by differentiation of a series of concentric layers of inter-connecting vascular strands, each layer derived from new cambial activity in pericycle tissue outside the existing vasculature. The ontogeny and mature structure of the anomalously thickened roots of certain species is described and the findings compared with published data for other genera of dicotyledons. A cladogram is presented to portray the phylogeny of the species of Daviesia included in the study, using 36 morphological features and the parsimony method to derive minimum length Wagner-type trees from a matrix of taxa character states. Evolution of the character of anomalous root thickening is concluded to have occurred early and possibly on two independent occasions during specialion of the genus.