Comparative Structure and Development of Pollen and Tapetum in Malpighiales, With a Focus on the Parietal Clade

Abstract

Malpighiales are one of the least resolved of the major angiosperm orders; more comparative data are needed to elucidate deep relationships and character evolution within the order. This article reevaluates pollen and tapetal characters, with a focus on one major subclade, the parietal clade. Pollen structure and, where possible, development are examined in representatives of the parietal clade from Passifloraceae (Passiflora, Turnera), Salicaceae (Populus, Salix), and Violaceae (Viola), and in Euphorbia (Euphorbiaceae), Hypericum (Hypericaceae), and Linum and Reinwardtia (Linaceae) from other Malpighiales. Pollen and tapetal characters in the parietal clade and selected outgroups are tabulated, using both original observations and an extensive literature search. Optimization of pollen and tapetal characters onto a recent molecular phylogeny indicates that lalongate endoapertures are a potential synapomorphy for the parietal clade. Passifloraceae (including the former Turneraceae) have some potential apom...