Proteaceae

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Proteaceae

Proteaceae is a family of flowering plants. Mainly restricted to the southern hemisphere, it is a fairly large family, with around 80 genera but less than 2000 species.

Description

Many proteaceae are highly variable, with Banksia in particular providing one of the most striking examples of adaptive radiation in plants. This variability makes it impossible to provide a simple, diagnostic identification key for the family, although individual genera may be easily identified.

Proteaceae are generally trees or shrubs, except for some Stirlingia species which are herbs. They are evergreen, with leaves that vary greatly in size, shape and margin. In many genera, the most obvious feature is the large and often very showy inflorescences, consisting of many small flowers densely packed into a compact head or spike. Even this character, however, does not occur in all Proteaceae: Adenanthos species, for example, have solitary flowers. In most Proteaceae species the pollination mechanism is highly specialised. It usually involves the use of a "pollen-presenter", an area on the style-end that presents the pollen to the pollinator.

Distribution and habitat

Proteaceae are mainly a southern hemisphere family, with its main centres of diversity in Australia and South Africa. It also occurs in Central Africa, South and Central America, India, eastern and south-eastern Asia, and Oceania.

It is a good example of a Gondwanan family, with taxa occurring on virtually every land mass considered a remnant of the ancient supercontinent Gondwana. The family and sub-families are thought to have diversified well before the fragmentation of Gondwana, implying that all of them are well over 90 million years old. Evidence for this includes an abundance of proteaceous pollen found in the Cretaceous coal deposits of the South Island of New Zealand. It is thought to have achieved its present distribution largely by continental drift rather than dispersal across ocean gaps.

Ecology

Many of the Proteaceae have specialised proteoid roots. These are dense masses of short lateral roots produced in the leaf litter layer during seasonal growth, and usually shrivelling at the end of the growth season. They are apparently an adaptation to growth in poor soil, greatly increasing the plants access to scarce water and nutrients by increasing the root's absorption surface. However, this adaptation leaves them highly vulnerable to dieback caused by the Phytophthora cinnamomi water mould, and generally intolerant of fertilization.

Taxonomy

Proteaceae is a fairly large family, with approximately eighty genera, but less than two thousand species. Well known genera include Protea, Banksia, Embothrium, Grevillea, Hakea, Dryandra and Macadamia.

It is recognised by virtually all taxonomists. Firmly established under classical Linnaean taxonomy, it is also recognised by the cladistics-based APG and APG II systems. It is placed in the order Proteales, whose placement has itself varied.

The framework for classification of the genera within Proteaceae was laid in 1975 by L. A. S. Johnson and Barbara Briggs. Their classification has been refined somewhat over the ensuing three decades, resulting in a fairly stable and widely accepted arrangement. Proteaceae is now divided into seven subfamilies: Persoonioideae, Bellendenoideae, Eidotheoideae, Proteoideae, Sphalmioideae, Carnarvonioideae and Grevilleoideae.

List of genera

Uses

Many Proteaceae species are cultivated by the nursery industry, as barrier plants and for their prominent and distinctive flowers and foliage. Some species are of importance to the cut flower industry, especially some Banksia and Protea species. Two species of the genus Macadamia are grown commercially for edible nuts.

References

External links

Proteales | Plant families

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