1. Sideroxylon
L. (buckthorn)
(Pennington, 1990)
Plants shrubs or
small trees with more or less milky sap, often with short spine-tipped branches
along the main stems. Leaves alternate or appearing fascicled at the tips of
short condensed branches, lacking stipules. Petioles absent or short. Leaf
blades simple, with entire margins, the smaller veins forming an intricate
network. Flowers axillary, solitary or in umbellate clusters, actinomorphic,
perfect, hypogynous. Calyx of 5 free or nearly free sepals, these overlapping,
often persisting in fruit. Corolla 5-lobed, white or sometimes
yellowish-tinged, the tube shorter than to about as long as the lobes, the
lobes ascending to spreading at maturity, each with a pair of short, petal-like
lobes or appendages at the base. Stamens 5, fused to the corolla tube,
positioned opposite the corolla lobes. Staminodes 5, similar in size, shape,
and color to the corolla lobes but usually somewhat more pointed at the tip,
fused to the corolla tube to the inside of the fertile stamens, positioned
alternate with the corolla lobes. Pistil 1 per flower, of (2–)5(–8) fused
carpels. Ovary superior, with (2–)5(–8) locules, usually hairy, at least toward
the base, tapered to the single style. Ovules usually 1 per locule, attached
toward the locule base. Stigma not conspicuous, a small obliquely positioned
receptive area at the tip of the style. Fruits drupelike berries, ovoid to
ellipsoid, green turning purplish black or black at maturity, the outer layer
leathery, usually shiny when ripe, the pulp somewhat milky, usually with 1
seed. Seeds obovoid to ellipsoid or nearly globose, the seedcoat relatively
thick, hard, shiny, light to dark brown, sometimes mottled on one side, the
base with a noticeable attachment scar. About 75 species, North America to
South America, Asia, Africa, and Madagasdcar.
Cronquist (1945,
1946) recognized three American genera as distinct from Sideroxylon,
which he restricted to the Old World. The 23 species of Bumelia Sw. were
said to differ from the closely related Mastichodendron (Engl.) H.J. Lam
and Dipholis A. DC. primarily in their divided corolla lobes and seeds
lacking endosperm. Pennington (1991), who reviewed the generic-level taxonomy
of the family worldwide, noted however that no single character served to
adequately separate these segregates and that some recently discovered
neotropical species blurred the perceived boundaries between the groups.
Accordingly, he chose to accept Sideroxylon in a broad sense, to include
a number of both New and Old World genera treated as distinct by earlier
authors (Pennington, 1990, 1991). His circumscription is adopted here.
The small
flowers of Sideroxylon species have an odd appearance. The stamens
appear to be sandwiched between two whorls of corolla lobes. The inner whorl,
however, is composed of petaloid staminodes.