Pollen morphology, exine structure and systematics of Acalyphoideae (Euphorbiaceae): Part 2. Tribes Agrostistachydeae ( Agrostistachys, Pseudagrostistachys, Cyttaranthus, Chondrostylis), Chrozophoreae ( Speranskia, Caperonia, Philyra, Ditaxis, Argythamnia, Chiropetalum, Doryxylon, Sumbaviopsis, Thyrsanthera, Melanolepis, Chrozophora), Caryodendreae ( Caryodendron, Discoglypremna, Alchorneopsis), Bernardieae ( Bernardia, Necepsia, Paranecepsia, Discocleidion, Adenophaedra) and Pycnocomeae ( Pycnocoma, Droceloncia, Argomuellera, Blumeodendron, Podadenia, Ptychopyxis, Botryophora)

Abstract

This is the second paper of an extensive study of pollen morphology and exine structure of Acalyphoideae (Euphorbiaceae) following the most recent system of Webster. Part 2 describes the pollen of 30 genera assigned to tribes Agrostistachydeae, Chrozophoreae, Caryodendreae, Bernardieae and Pycnocomeae. In Agrostistachydeae, members of Agrostistachys and Pseudagrostistachys have similar but unspecialized pollen; grains of Cyttaranthus have weakly suprareticulate tecta of widely varying thickness and small densely spaced columellae; pollen of Chondrostylis has a croton sculpture and precisely defined bridges of ectexine over the endoaperture. Of the 11 genera assigned to tribe Chrozophoreae, pollen of Caperonia has prominent opercula, thick exines and punctate tecta, pollen of Ditaxis and Argythamnia is colpate, has large columellae, and the unevenly thick and complete tecta associated with suprareticulate sculpture or derivations thereof, and pollen of Chiropetalum has operculate apertures, diminutive columellae, and an incomplete finely reticulate tectum, characteristics which argue against a supposedly close relationship to Ditaxis and Argythamnia. Three of the four genera assigned to subtribe Doryxylinae, Doryxylon, Sumbaviopsis, and Melanolepis have similar pollen — thin exines with irregular foot layers, and irregular short columellae, whereas pollen of the fourth genus, Thyrsanthera, has thicker exines with a well-defined foot layer and more elongate columellae. The eight examined species of Chrozophora have 6–9 aperturate pollen and robust exines; two species have punctate tecta and zonorate endoapertures; the remaining species have heterobrochate tecta and lolongate endoapertures. The three genera comprising Caryodendreae, Caryodendron, Discoglypremna and Alchorneopsis, have small 3-colporate pollen with punctate tecta. Pollen of the five genera assigned to tribe Bernardieae, Bernardia, Necepsia, Paranecepsia, Discocleidion and Adenophaedra is of a similar, but unspecialized type — a punctate, deeply punctate, or microreticulate tectum, small endoaperture, and usually a prominent margo. The present concept of tribe Pycnocomeae as comprising Pycnocoma, Droceloncia, Argomuellera, Blumeodendron, Podadenia, Ptychopyxis and Botryophora is not supported by the pollen data. Members of Pycnocoma have pollen with a derived exine structure — a conspicuously thick endexine throughout the grain, threadlike foot layers, and columellae reduced to a point on the proximal side of the tectal elements. The pollen data are somewhat ambiguous about a close relationship between Droceloncia and Argomuellera, the two remaining genera in the subtribe Pycnocominae. The genera allied as subtribe Blumeodendrinae, Blumeodendron, Podadenia, Ptychopyxis, and Botryophora, share pollen with short narrow colpi, a croton sculpture, and mostly irregular columellae.