Pollination And Dispersal

Flowers of almost all Aloe species are diurnal, tubular, brightly coloured red or yellow, unscented and produce abundant nectar. These features point to ornithophily as the pollination syndrome, and sunbirds (Nectariniidae) are frequent visitors to aloe flowers in the field and in African gardens (Figure 1.2).

Although they are not typical melittophilous flowers, aloes are also visited by bees. In some areas, especially in South Africa, the flowering of aloes is important in apiculture, though it is reported that the nectar and pollen of some species can affect the behaviour of bees, making them vicious (Watt and Breyer-Brandwijk, 1962). The abundance of nectar produced by the flowers of some species is such that even baboons have been seen collecting flowers in order to suck the nectar (Reynolds, 1950). In West Africa some wasps were captured on flowers of A. buettneri, and dissection of the gut

Pollination And Dispersal
Figure 1.2 Sunbird on Aloe cheranganiensis flower (see Colour Plate 2).

revealed that they had been eating pollen. Pollination of flowers of different shapes, such as the white campanulate flowers of A. albiflora Guillaumin, has yet to be investigated. The Madagascan Aloe suzannae Decary is exceptional in the genus in having nocturnal fragrant flowers, presumably pollinated by nocturnal animals such as bats and small lemurs.

Almost all aloes are self-incompatible, though oddly enough the flowers are protan-drous (anthers ripen and pollen is dispersed before the stigma is receptive) and so self-pollination would not occur anyway. The species formerly in the genus Lomatophyllum are reported as exceptions in being self-compatible (Lavranos, 1998). In an area where two or more species of Aloe flower at the same time, the main pollen vectors, sunbirds, fly indiscriminately from one species to another. Consequently hybridisation is frequent. Reynolds (1950, 1966) reported many natural hybrids, especially in South Africa, and Newton (1998) reported a number in East Africa. In gardens and greenhouse collections, where there might be only one specimen of each species, almost all seeds produced are of hybrid origin. In a tropical garden, hybrid seedlings can become established quickly, and numerous garden aloes that are difficult to identify are undoubtedly of this origin.

Most aloes produce capsules, dry dehiscent fruits that split open at maturity to release the seeds. As the inflorescences sway in the wind the seeds, which are winged, are thrown out and blown away. Species that were formerly included in the small genus Lomatophyllum have berries, indehiscent fruits with fleshy walls. The seeds of these species are without wings. The berries have been observed to fall to the ground from the parent plant and decay on the ground, thereby releasing the seeds.

In the natural habitat young seedlings grow quickly in order to build up sufficient aqueous tissue to survive their first dry season. They are usually found amongst rocks or below shrubs (nurse plants), which give protection from the hot sun and from browsing animals.

Bulbil formation is reported as a regular occurrence in A. bulbillifera H.Perrier (Madagascar) and A. patersonii B.Mathew (Democratic Republic of Congo). The bulbils are formed on the peduncle and inflorescence branches. This phenomenon was also observed once on a cultivated plant of the Kenyan A. lateritia.

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Aloe and Your Health

Aloe and Your Health

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