Changes

{{DISPLAYTITLE:''Erythroxylum'' (PROSEAMedicinal plants)}}

:Chromosome number: ''x''= 12;''E. coca'': 2''n''= 24,''E. novogranatense'': 2''n''= 24

*''Erythroxylum coca'' Lamk, *''E. novogranatense'' (Morris) Hieron.

''Erythroxylum'' , which has about 250 species, is pantropical and its centre of diversity is in the Andes and the Amazon basin in South America. There are 6 indigenous species and 2 cultivated species in the Malesian region. The two species that are medicinally most important, ''E. coca'' and ''E. novogranatense'' , contain cocaine. They are native to South America, and were introduced into South-East Asia by the end of the 19th Century.

*Shrubs or small trees. *Leaves simple, alternate, distichous, entire; stipules intrapetiolar, inserted semi-amplexicaulously, mostly entirely connate, rarely bifid, sometimes emarginate or 2-toothed at the apex, often bicarinate, long-persistent or early caducous, leaving a distinct scar, involute in bud, the margins leaving a subpermanent trace as 2 longitudinal lines on the upper leaf surface ("areolate"). *Flowers in axils of leaves, solitary or in clusters, bisexual, 5-merous, actinomorphic, often heterodistylous, or even heterotristylous; pedicel slightly thickened, often only under the calyx, with 2 bracteoles at the base; calyx campanulate, persistent; petals free, alternating with the calyx lobes, caducous, quincuncial in bud, nearly always provided with an emarginate or 3-lobed ligule inserted on the apex of the claw; stamens in 2 whorls of 5, persistent, filaments towards the base connate into a staminal tube, anthers ellipsoid, basifixed, cordate at the base, 2-celled; ovary superior, (1-)3-celled, normally only 1 cell fertile, each cell with 1 ovule, ovules pendulous, anatropous, with a ventral raphe, styles 3, erect, free or partly connate or stigmas sessile. *Fruit a drupe. *Seed with or without endosperm, embryo oblong, erect, cotyledons flat to plano-convex, plumule absent, radicle distinct.

''E. novogranatense'' seed starts to germinate in 2-3 weeks after planting. Three months after germination the plants may have attained a height of 15 cm. The first harvest, usually 1-3 years after transplanting into the field, consists of the main shoot that is pruned to promote frame formation as in tea ( ''Camellia sinensis'' (L.) Kuntze). Consecutive pruning is carried out when coca develops flower buds; this coincides with a maximum in harvestable leaves. Leaf harvesting brings ''E. coca'' plants from the vegetative into the reproductive development phase.

Cocaine-rich leaves are obtained from 4 taxa: ''E. coca'' var. ''coca'' (Bolivian or Huánoco coca), ''E. coca'' var. ''ipadu'' Plowman (Amazonian coca), ''E. novogranatense'' var. ''novogranatense'' (Colombian coca) and ''E. novogranatense'' var. ''truxillense'' (Rusby) Plowman (Trujillo coca). ''E. coca'' var. ''coca'' is considered the ancestor, while ''E. novogranatense'' var. ''truxillense'' is derived from it, and ''E. novogranatense'' var. ''novogranatense'' derived from ''E. novogranatense'' var. ''truxillense'' . Cultivation and selection has probably been the main selective force. ''E. coca'' var. ''ipadu'' is considered to be a cultivar selected by man from ''E. coca'' var. ''coca'' . Wild populations of ''E. coca'' var. ''coca'' are found in the eastern Andes, but the other 3 taxa are only known as cultivated plants. Crosses between ''E. coca'' var. ''coca'' and ''E. novogranatense'' var. ''novogranatense'' have failed. Crosses between ''E. coca'' and ''E. novogranatense'' var. ''truxillense'' have been made, but gave abnormal, dwarfed progenies.

In the past ''Erythroxylum'' has been incorporated in different families, i.e. ''Malpighiaceae'' , ''Linaceae'' and ''Erythroxylaceae'' . In recent systems of classification it is widely accepted that the ''Erythroxylaceae'' differ from the ''Malpighiaceae'' by their unwinged fruits that do not split into 3 nut-like parts at maturity, and from the ''Linaceae'' by their ligulate petals and 3-locular ovary with only one fully developed locule.

''E. coca'' var. ''coca'' is well adapted to the eastern Andes of Peru and Bolivia, an area of humid, tropical montane forest, whereas ''E. coca'' var. ''ipadu'' is cultivated in the lowland Amazonian basin. ''E. novogranatense'' is cultivated in drier regions in South America. However, ''E. novogranatense'' var. ''novogranatense'' is very adaptable to varying ecological conditions, and grows well in both humid and dry areas, and at low and higher altitudes. In Java, ''E. novogranatense'' has been cultivated from sea-level to 1000 m altitude, with best results at 400-600 m. In controlled environment studies, the optimum average daily temperature for leaf growth for both ''E. coca'' and ''E. novogranatense'' var. ''novogranatense'' was found to be around 27°C27 °C, whereas leaf growth was generally higher at photosynthetic photon flux densities of 250 or 400 μmol.m^-2.s^-1than at 155 μmol.m^-2.s^-1. Environmental effects on the cocaine concentration in the leaves were smaller, so that total cocaine production per plant was largely a function of leaf mass, with environmental conditions that stimulated leaf growth giving higher cocaine yields. Both species grow on soils with low pH, and a greenhouse study has shown that the optimum pH for biomass accumulation of ''E. coca'' and ''E. novogranatense'' is as low as 3.5 and 4.7-6.0, respectively.

''E. novogranatense'' var. ''novogranatense'' , ''E. novogranatense'' var. ''truxillense'' and ''E. coca'' var. ''coca'' have to be reproduced by seed, because vegetative propagation is difficult. However, ''E. coca'' var. ''ipadu'' does not produce seed and is propagated by stem cuttings. It cannot reproduce without human interference. Cultivated ''E. novogranatense'' var. ''novogranatense'' produces abundant seed and is easy to propagate. Seed viability decreases rapidly. Germination percentages of ''E. coca'' and ''E. novogranatense'' seed were found to decrease from around 95% and 89% directly after harvesting to 29% and 0%, respectively, after 24 days' storage at 4°C4 °C. Coca seedlings are usually sown in shaded nurseries and transplanted to the field when they are about one year old and 20-25 cm tall. In the field, they are planted at a spacing of 1-2 m. The actual time of transplanting and the spacing of the plants varies with climatic factors and whether coca is interplanted or cultivated as a sole crop.

''Erythroxylum'' spp. are susceptible to Fusarium wilt, caused by the host-specific fungus ''Fusarium oxysporum'' , which is considered a potential mycoherbicide to combat illegal coca production. Symptoms are vascular wilt and permanent defoliation.

When the leaves of coca are used for cocaine production, they are dried in the sun or artificially. Temperatures should not exceed 40°C40 °C, because the cocaine content of the leaves decreases at higher temperatures. The leaves are considered dry when they can be broken. In Asia, dried leaves are ground, pulverized and packed in plastic bags, while in South America they are pressed into bales of about 50 kg for transport. Leaves intended for chewing in South America must keep their form and colour and are dried more carefully.

The gene pool of cultivated ''E. coca'' has changed little over 5000 years, and wild or abandoned ''E. coca'' shows no morphological and genetic differences from cultivated ''E. coca'' . No germplasm collection and breeding programmes are known to exist.

*R.C.K. Chung & M. Brink