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A.M.W. Mennega
Wood anatomy of the subfamily Euphorbioideae
A comparison
with subfamilies Crotonoideae and Acalyphoideae and the implications for
the circumscription of the Euphorbiaceae
IAWA J. 26 (1): 1-68
The wood anatomy was studied of 82 species from 34 out of 54 genera in the
subfamily Euphorbioideae, covering all five tribes recognized in this
subfamily. In general the woods show a great deal of similarity. They are
characterized by a relative paucity of vessels, often arranged in short to
long, dumbbell-shaped or twin, radial multiples, and by medium-sized to
large intervessel pits; fibres often have gelatinous walls; parenchyma
apotracheal in short, wavy, narrow bands and diffuse-in-aggregates; mostly
uni- or only locally biseriate rays, strongly heterocellular (except Hippomane, Hura and Pachystroma).
Cell contents, either silica or crystals, or both together, are nearly
always present and often useful in distinguishing between genera. Radial
laticifers were noticed in most genera, though they are scarce and
difficult to trace. The laticifers are generally not surrounded by special
cells, except in some genera of the subtribe Euphorbiinae where radial
laticifers are comparatively frequent and conspicuous.
Three of the five tribes show a great deal of conformity in their anatomy.
Stomatocalyceae, however, stand apart from the rest by the combination of
the scarcity of vessels, and mostly biseriate, vertically fused and very
tall rays. Within Euphorbieae the subtribe Euphorbiinae shows a greater
variation than average, notably in vessel pitting, the frequent presence of
two-celled parenchyma strands, and in size and frequency of the laticifers.
Data from surveys of the two other subfamilies of the uniovulate euphorbs,
Acalyphoideae and Crotonoideae are compared and their relationships are
discussed. The comparison of Euphorbioideae, Acalyphoideae, and
Crotonoideae shows a great anatomical conformity with only a marked
difference in the presence of laticifers: scarce in Acalyphoideae and
Crotonoideae but nearly always present and often frequent in
Euphorbioideae. All in all, wood anatomy supports a narrower family concept
of Euphorbiaceae, including only Acalyphoideae, Crotonoideae, and
Euphorbioideae, while excluding Phyllanthoideae and Oldfieldioideae, as has
recently been advocated by several authors.
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