| Despite the unparalleled diversity of plant life forms in the dry tropics, little is known about the systematics or evolution of plants in these areas. This study aims to gather data to examine the role of heterochrony in generating this diversity among the 13 species of Moringa, the sole genus of the Old World dry tropical family Moringaceae. Four life forms were identified in Moringa: (1) Bottle trees, which store water in trunks and roots; (2) Sarcorhizal trees, which have slender trunks and elongate tuberous roots; (3) Slender trees, which have tough, fibrous, slender trunks and roots; (4) Tuberous shrubs, which have thin stems and massive tubers below ground. Anatomical studies of stems and roots using light microscopy (LM) and scanning electron microscopy (SEM) encountered anatomical homogeneity within each of these categories except among the two species of sarcorhizal trees, which showed differing affinities to members of the tuberous shrubs. To reconstruct the phylogeny of Moringa, parsimony analyses were conducted of over 1500 characters in four data sets separately and combined (DNA sequence of the ITS, PPC, and trnG regions and morphological characters). Congruence among these data sets was confirmed using the ILD and Templeton tests. In the preferred tree, which derives from the analysis of all the data, the bottle trees appear as a basal paraphyletic assemblage, with the slender trees and tuberous shrubs as monophyletic clades. Within the tuberous clade, phylogenetic reconstruction confirms the suggestion based on anatomical study of the placement of the two sarcorhizal tree species. Additional molecular and morphological studies were conducted to identify synapomorphies of the Moringaceae, its sister taxon Caricaceae, and of the Caricaceae+Moringaceae clade, and to examine intergeneric relationships within this clade. Analysis of sequence of the chloroplast gene rbcL confirms the monophyly of both families within the clade of glucosinolate producing plants. Synapomorphies of the clade include subulate glands on the leaves of both families. SEM and LM studies of floral ontogeny of 10 species of Moringa show that early stages are similar across the family and diverge progressively throughout ontogeny. It is hypothesized that bilaterally symmetrical flowers are derived via peramorphosis from actinomorphic ancestors. |
