Tuesday, April 29, 2008

grevillea

Now that it's getting cooler, our grevilleas are flowering and attracting lots of bees. Their flower structure is intricately beautiful. A photo makes it much easier to appreciate their delicacy and complexity.

The genus Grevillea is probably the most popular and widely cultivated of all of Australia's plant genera. The reasons for this are pretty obvious to anyone who's seen one. They are colourful and in many cases attrack honey eating birds. They occur in numerous shapes and sizes so that there is a Grevillea for almost any conceivable garden situation.

Grevillea is a member of the Protea family (Proteaceae) and its close relatives include Banksia, Hakea, Dryandra, Isopogon and Telopea (the Waratah). Grevillea is named after Charles Francis Greville who was one of the founders of the Royal Horticultural Society in 1804. There are over 300 species in the genus, most of which are endemic to Australia but a few species occur in Papua New Guinea and islands to Australia's north.

The flowers of Grevillea species are quite small but they occur in clusters (an inflorescence) which, in some species, may consist of perhaps 100 or more individuals. The inflorescences can be quite variable in arrangement but two that are commonly recognised are the "spider" flower arrangement,in which the flower styles arise from a rounded inflorescence like the legs of a spider, and the "toothbrush" arrangement, in which the individual flowers are grouped into a short inflorescence along one side of the floral axis. Another common inflorescence, particularly in cultivated plants, is the large "brush" shape where the flowers are clustered into cylindrical racemes usually at the ends of branches where they are very conspicuous.

Grevilleas can be seen in flower at most times of the year but winter to early spring would be the peak flowering period. Following flowering, thin-walled seed pods develop, each containing one or two seeds. The pods open when the seed is mature. Seeds often have a papery wing to allow them to be distributed by the wind but this is not a universal feature. The majority of grevilleas occur in areas where bushfires are relatively frequent. Although a few can regenerate from lignotubers or epicormic buds after a fire, most are killed by fire and rely on seed germination for their continued survival.

Most grevilleas are small to medium shrubs but some are prostrate and a few can become large trees. The various species hybridise readily and most of the named cultivars and hybrids available in nurseries have resulted from chance hybridisation. Some deliberate breeding is being undertaken by Grevillea enthusiasts.

One of the great features of grevilleas in gardens (apart from the colourful flowers) is that many attract honey-eating birds which act as pollinators for the plants. A number of species rely on other methods of pollination, eg, beetles, moths, bees, ants, and even small marsupials.

Grevilleas were used by the aboriginal tribes for food. A cool drink was obtained from the roots which was used as sustenance in desert crossings. The nectar from the flowers was made into a drink by soaking the flower heads in water. A paste was made by mashing the bark of some grevilleas and this was used to heal earache, spear wounds, skin sores and even rubbed on women’s breasts to induce lactation. These pastes were also used for tribal markings. Queensland aborigines utilised the gum of one grevillea as ‘cement’ and used it to attach flints to axes and spears.

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