Ovules and seeds in Euphorbioideae (Euphorbiaceae): structure and systematic implications

Abstract.

Ovule and seed structure in Euphorbioideae, one of the five euphorbiaceous subfamilies, is surveyed to evaluate its systematic implications on the basis of 79 species representing four of five tribes. All Euphorbioideae, like two other "uniovulate" subfamilies Acalyphoideae and Crotonoideae, but unlike most of two "biovulate" subfamilies Oldfieldioideae and Phyllanthoideae, consistently have a persistent and palisadal exotegmen composed of radially elongate, sclerotic, and pitted cells. Within Euphorbioideae, the tribe Stomatocalyceae (also with the palisadal exotegmen) is unusual in having vascular bundles in outer integument and clearly distinct from the remaining Euphorbioideae and the other "uniovulate" subfamilies. With the exclusion of Stomatocalyceae, Euphorbioideae are not anatomically divided into major groups such as a pseudanthial and a non-pseudanthial clade, but instead have some remarkable diversity within a tribe, a subtribe, and even a genus in the three ovule and seed characters: (1) the thickness of the inner integument, (2) the thickness of the outer integument, and (3) the presence or absence of an aril. Groups of genera and species wrapped by different combinations of their characteristics, however, are not necessarily harmonized with tribal or subtribal classifications available. Anatomical similarities and dissimilarities presented in this paper, as well as relationships among taxa presented in the classifications available, will be critically evaluated in the light of results of ongoing molecular phylogenetic analyses.