VETIVER'S CLOSE RELATIVES

Perhaps the most promising alternatives to vetiver will be found among its own wild relatives. As has been noted already, vetiver has a dozen or so close relatives (see sidebar, page 116). These species belong to the same genus, but so far none has been explored for its erosion-controlling capabilities. Nothing suggests that any of them can match (let alone surpass) vetiver itself, but they deserve research attention nonetheless.

All these vetiver relatives are wild plants. Presumably, they are all fertile and spread by seed. However, none is known to be a weed or nuisance of any moment.

These plants are widely scattered. Four are native to Queensland, Australia, and some of those can also be found in the neighboring areas of New South Wales and Northern Territory, as well as in New Guinea. One is native to India—not to the northern plains and swamps like vetiver itself, but to the southwestern region in Karnataka. One is native to the islands of Mauritius and Rodrigues in the Indian Ocean. And two are native to the African continent.

The fact that these grasses mostly occur in riverine basins and other wet areas would seem to argue against their usefulness on hill slopes. However, vetiver itself also comes from a soggy background. By and large, they are robust plants with stout root stock and erect stems. Such features might make them good for erosion control, but the roots on at least one are said to grow horizontally, which would pose problems in hedges running across farms or forests.

VETIVER'S DISTANT RELATIVES

Lemongrass

Apart from vetiver itself, lemongrass (Cymbopogon citratus) has probably been used in hedges against erosion more than any other grass species. It is planted on bunds for soil conservation as well as on hillsides and road cuts in Central America and elsewhere in the tropics.

It has a number of vetiver's vital features. For example, its large and strong stems can hold back soil, even when it is planted in a single line. It has wide adaptability and the capacity to survive where terrain is difficult and conditions terrible. It tillers strongly, forming large tussocks. Because it seldom flowers, it does not spread by seedlings.

All of these are features favorable for erosion-control hedges, of course. But in practice, lemongrass does not seem to work as well as



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