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)

This is the first paper of an extensive study of pollen morphology and exine structure of the Euphorbiaceae. To date, the pollen of more tha n 600 species has been examined, most of them in transmission electron microscopy as well as light microscopy and scanning electron microsco py. Pollen of Acalyphoideae, tribes Clutieae, Pogonophoreae, Chaetocar peae, Pereae, Cheiloseae, Erismantheae pro parte, Dicoelieae, Galearie ae, and Ampereae is described, documented by electron micrographs, and the systematic implications of the data are discussed. Almost all mem bers of the above tribes have pollen that is 3-corporate in which the endoaperture frequently has well-defined polar margins but diffuse lat eral 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 d istal tips of columellae. Pollen of Pogonophora has large columellae a nd a thick punctate tectum, characteristics that are shared with Trigo nopleura, a genus assigned to Chaetocarpeae. The genus Chaetocarpus ha s pollen with small columellae and microrugulose tecta. Most species o f Pera have thin exines characterized by small columellae; pollen of P . arborea is intectate; pollen of P. distichophylla is thick-walled wi th massive columellae and a thick foot layer-endexine. Grains of Cheil osa and Neoscortechinia (Cheiloseae) have echinate tecta, a distinctio n reinforced by an almost identical exine structure. The single specie s of Moultonianthus (Erismantheae) has pollen with reticulate tecta an d well-developed columellae while Erismanthus has a punctate tectum an d small irregular columellae. Pollen of Dicoelia has a weakly supraret iculate tectum and columellae that are poorly differentiated from a ch anneled tectum. Grains of Galearia and Microdesmis have thin exines wi th deeply punctate tecta in contrast to pollen of the third genus of G alearieae, 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 a nd partially covered lumina, and the latter has smaller columellae and an unmodified reticulate tectum. The data from exine structure: suppo rt the monogeneric concept of Clutieae; show that Pogonophora is not c losely related to Clutia, suggest that Trigonopleura may be more close ly related to Pogonophoreae than to Chaetocarpeae; are anomalously, so metimes conspicuously, variable within Pei-a; support the present conc ept 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 biovul ate genus Dicoelia is isolated in the uniovulate Acalyphoideae; and in dicate that the similarity in SEM between pollen of Amperea and that o f Monotaxis is superficial, and that the two genera are not as closely related as previously thought. (C) 1998 Elsevier Science B.V. All rig hts reserved.