Pollen morphology, exine structure and systematics of Acalyphoideae (Euphorbiaceae) Part 1. Tribes Clutieae ( Clutia), Pogonophoreae ( Pogonophora), Chaetocarpeae ( Chaetocarpus, Trigonopleura), Pereae ( Pera), Cheiloseae ( Cheilosa, Neoscortechinia), Erismantheae pro parte ( Erismanthus, Moultonianthus), Dicoelieae ( Dicoelia), Galearieae ( Galearia, Microdesmis, Panda) and Ampereae ( Amperea, Monotaxis)

Abstract

This is the first paper of an extensive study of pollen morphology and exine structure of the Euphorbiaceae. To date, the pollen of more than 600 species has been examined, most of them in transmission electron microscopy as well as light microscopy and scanning electron microscopy. Pollen of Acalyphoideae, tribes Clutieae, Pogonophoreae, Chaetocarpeae, Pereae, Cheiloseae, Erismantheae pro parte, Dicoelieae, Galearieae, and Ampereae is described, documented by electron micrographs, and the systematic implications of the data are discussed. Almost all members of the above tribes have pollen that is 3-colporate in which the endoaperture frequently has well-defined polar margins but diffuse lateral ones. The tectum and exine structure are more variable. Pollen of Clutia has branched columellae and a tectum in which the ‘floors’ of the lumina are formed not by the foot layer but by the fusion of the distal tips of columellae. Pollen of Pogonophora has large columellae and a thick punctate tectum, characteristics that are shared with Trigonopleura, a genus assigned to Chaetocarpeae. The genus Chaetocarpus has pollen with small columellae and microrugulose tecta. Most species of Pera have thin exines characterized by small columellae; pollen of P. arborea is intectate; pollen of P. distichophylla is thick-walled with massive columellae and a thick foot layer-endexine. Grains of Cheilosa and Neoscortechinia (Cheiloseae) have echinate tecta, a distinction reinforced by an almost identical exine structure. The single species of Moultonianthus (Erismantheae) has pollen with reticulate tecta and well-developed columellae while Erismanthus has a punctate tectum and small irregular columellae. Pollen of Dicoelia has a weakly suprareticulate tectum and columellae that are poorly differentiated from a channeled tectum. Grains of Galearia and Microdesmis have thin exines with deeply punctate tecta in contrast to pollen of the third genus of Galearieae, Panda, which has a thick exine with and a reticulate tectum. The two genera of Ampereae, Amperea and Monotaxis, have pollen with reticulate tecta, but the former genus has large elongate columellae and partially covered lumina, and the latter has smaller columellae and an unmodified reticulate tectum. The data from exine structure: support the monogeneric concept of Clutieae; show that Pogonophora is not closely related to Clutia, suggest that Trigonopleura may be more closely related to Pogonophoreae than to Chaetocarpeae; are anomalously, sometimes conspicuously, variable within Pera; support the present concept of Cheiloseae and the close relationship between and the isolation of Cheilosa and Neoscortechinia; support a close relationship between Galearia and Microdesmis, but not with Panda; suggest that the biovulate genus Dicoelia is isolated in the uniovulate Acalyphoideae; and indicate that the similarity in SEM between pollen of Amperea and that of Monotaxis is superficial, and that the two genera are not as closely related as previously thought.