Saturday May 27, 2017

Marloth and its lack of grass


Grasses belong to the plant Family Poaceae which is one of the largest plant families in the world with about 9 700 species world-wide. Of this number, 967 species have been described from Southern Africa, of which 329 are endemic to the region and about 115 introduced. Wheat, maize, sugar cane, rice and sorghum are all grasses.

Grasses are characterised by 'nodes' along the stem - or jointed stems - as opposed to 'sedges' which have stems with no joints and which belong to another Family. For proper identification, the botanical names of grasses should be used as common names can be very misleading.

All grasses belong to the classification known as Monocotyledons, as opposed to trees and shrubs which generally belong to Dicotyledons. All Monocots grow from seed with only one leaf shoot, while Dicots grow from seed with two leaf shoots. The importance of remembering this is that Monocots grow from the base of the stem whereas Dicots grow from the upper or outer tips of the stem and branches. All grasses therefore grow from the base of the stem and leaves.

The ecology of Southern Africa's grasslands is affected by grazing, fire, rainfall etc. - all these factors play a significant role in the species composition and health of a grassland.

If herbaceous plants and trees (Dicots) are browsed or bitten by animals, the growing tip is destroyed and the plant reacts by putting out alternate shoots. This has the effect of causing the plant to 'coppice' and the plant generally produces a denser growth. However, if grasses (Monocots) are bitten or grazed by animals, the growing part is not destroyed and it will continue growing from the base, with the bitten tips remaining a feature. This is an extremely important difference between the Monocots and Dicots. The utilisation of grass species by grazers can thus easily be identified due to the amount of foliage removed.

Through the process of 'photosynthesis', leaves produce carbohydrates (food energy) from sunlight, minerals, CO2 and water. The energy to produce growth, however, is obtained from energy stored in the roots. As the grass plant grows so it withdraws from the roots until it has manufactured enough energy to restore that taken from the roots. If a plant is grazed immediately and frequently as it tries to grow, it will be unable to replace root energy and the effect is that the rootstock will be weakened or diminished and eventually the plant can die.

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