Agriculture Reference
In-Depth Information
petiole is up to 1 cm long and canaliculate above; the blade is ovate-oblong to elliptical-oblong,
rarely lanceolate, 5-14 × 2-5 cm, with base attenuate, apex abruptly acuminate, obtuse, or minutely
apiculate, entire, thick-papery, glabrous, pale green above, paler beneath, with 3-6 pairs of strongly
curved lateral veins looped near the margin. Inflorescence occurs in an unbranched catkin, axillary
or terminal on a short branch, solitary but male inflorescences at the apex of branches and often
in groups of 3, up to 8 cm long, jointed, with a peduncle 1-1.5 cm long, with a pair of scale-like,
triangular bracts; male inflorescence occurs with slender internodes and whorls of flowers at nodes;
female inflorescence has slightly turbinate internodes and 2-3 flowers at each node. Flowers are
small, about 2 mm long, with moniliform hairs at the base and an envelope; male flowers have a
tubular envelope and exerted staminal column bearing 2 anthers; female flowers have a copular
envelope and naked, sessile ovule. Seed, resembling a drupe, is orange-red when ripe and ellipsoid,
10-15 × 4-8 mm, and enclosed in the fleshy envelope.
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Ethnomedicinal Uses —
Both species are used as a vegetable, eaten raw or cooked in soups and
salads. The aerial parts have been used in traditional medicine for the treatment of diabetes, piles,
and high blood pressure; as medicine against enlarged spleen and sore throat; and as a purgative. In
the Central African Republic, the leaves are eaten to treat nausea and as an antidote to arrow poison
made from
Periploca nigrescens
Afzel. In Cameroon, the leaves are chewed to mitigate the effects
of drunkenness, and they are taken as an enema against constipation and to ease childbirth. They
are also used to treat boils and fungal infections on the fingers.1140
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Constituents —
Gnetum
leaves contain C-glycosylflavones, 2″-xylosylisoswertisin and 2″-gluco-
sylisoswertisin. Perhaps of chemotaxanomic importance is the presence of 2″-O-rhamnoylisoswertisin
and apigenin-7-hesperidoside and the absence of vitexin and 2″-O-glycosylvitexin in
Gnetum afri-
canum
.
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Stilbenes, as well as their dimeric, polymeric, and hydroxylated derivatives, have been
isolated from some
G. africanum
and other
Gnetum
species.
Pharmacological Studies —
Most of the studies on eru are on its nutritional properties. It
has been shown that extracts of the leaf of
Gnetum africanum
induced vaginal openings and
increased weights of the uterine muscle in a manner similar to the effect of repeated administra-
tion of estrogen to immature female rats. The uterine muscle enlargement suggests the antifer-
tility potential of the popular vegetable in the female reductive system of rats.
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However, the
result on rats may not correlate directly to human use. The antioxidant quality of
Gnetum
has
been evaluated by the determination of lag time, concentration of polyphenol that will inhibit
50% of oxidation of LDL plus very low-density lipoprotein (VLDL) (IC
50
) and phenol antioxidant
index (PAOXI). It was observed that both hydrolyzed and nonhydrolyzed extracts were better
antioxidants than vitamin E in the inhibition of copper-mediated LDL-plus-VLDL oxidation.
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This observation is interesting in view of the reported presence of the antioxidant compound
resveratrol and stilbenes in
Gnetum
.
622,623
Agriculture —
Gnetum
is still collected from wild species. But, trial cultivations have begun
in Cameroon, Nigeria, and Benin Republic. The main problem is that the plant in its natural habitat
seems to prefer shaded forest canopies. In experiments in Cameroon, propagation by seed was dif-
ficult because the seed is slow to sprout, with germination taking 1 year or more. Perhaps the seeds
need pretreatment, such as passing through the intestines of a bird, fruit bat, squirrel, or other ani-
mal, before they germinate. Seed is normally found only in the tree canopy. Seed collection is thus
far from easy, a further reason why eru is hardly cultivated.
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Experimental cultivation using leafy
stem cuttings have produced encouraging results.
Commerce —
Even with the little work done on the chemistry and pharmacology of eru,
there is already a high demand for this highly priced and much prized vegetable. With its
remarkable antioxidant profile and reputed nutrient properties, the current trade within the West
and Central African zone will likely expand. The major limitation remains the scarcity of the
plant in the wild.
