A NOTE ON REMARKABLE EXINES IN ACALYPHOIDEAE (EUPHORBIACEAE)

As part of an extensive study of pollen of Euphorbiaceae that combines transmission electron microscopy with scanning electron microscopy, d istinctive exines are reported and documented for certain Acalyphoidea e. Cheilosa and Neoscortechinia, which comprise the tribe Cheiloseae, are the only Acalyphoideae with an echinate tectum, bur their aperture s and exine structure do not support a relationship to Oldfieldioideae . In Ditaxis, one of the three mesocolpia is much smaller than the oth er two and the pollen can be easily distinguished from all other Eupho rbiaceae. In SEM, the tectum of Pycnocoma appears almost complete, but in TEM the exine consists of irregular, mostly discrete rectal elemen ts that narrow to points (=columellae) at the interface with the threa dlike footlayer. The operculate grains of Alchornea and Boquillonia ha ve exines with a poorly differentiated double layer of columellae in t he mesocolpium, but nearer the endoaperture the lower tier becomes gre atly elongated and appears to rest directly on the endexine. Plukeneti a polyadenia has a complete tectum and a thick exine with a predominan t infratectum of large, occasionally branched columellae that nearer t he tectum are combined with densely spaced granules. Plukenetia pennin ervia has a reticulate tectum of crenate muri and short, sparse colume llae. The pollen diversity in Acalyphoideae suggests that the subfamil y, many tribes and even genera may not be monophyletic.