Proteaceae
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 Inflorescence of Protea cynaroides | ||||||||||
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| About 80, see text |
Proteaceae is a family of flowering plants. Mainly restricted to the Southern Hemisphere, it is a fairly large family, with around 80 genera but fewer than 2000 species. Together with the Platanaceae and Nelumbonaceae they make up the order Proteales.
Description
Many proteaceae are highly variable, with Banksia in particular providing one of the most striking examples of adaptive radiation in plants[1]. 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.[2]
Distribution and ecology
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[3]. Only two species are known from New Zealand although fossil pollen evidence suggests there were more previously[4].
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. [5]
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.[3] However, this adaptation leaves them highly vulnerable to dieback caused by the Phytophthora cinnamomi water mould, and generally intolerant of fertilization. Due to these specialized proteoid roots, the Proteaceae are one of few flowering plant families which do not form symbioses with arbuscular mycorrhizal (AM) fungi.
Taxonomy
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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.[6] 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. Gevuina avellana (Chilean hazel) tree is cultivated for its nuts in Chile and New Zealand, which are edible, and are used in pharmaceutical industry for skin treatment because of its moisturizing properties and as ingredient in sunscreens. Among the trees within the family which produce nuts it is the hardiest. It is also planted in the British Isles and the Pacific Coast of the United States because it is a tropical aspect (and related) tree that can grow in cool climates.
References
- ↑ Mast, A. R. and Givnish, T. J. (2002). "Historical Biogeography and the Origin of Stomatal Distributions in Banksia & Dryandra (Proteaceae) Based on Their cpDNA Phylogeny". American Journal of Botany 89 (8): 1311–1323. ISSN 0002-9122.
- ↑ Watson, L. and Dallwitz, M. J. (3 May 2006). "Proteaceae". The Families of Flowering Plants: Descriptions, Illustrations, Identification, Information retrieval. Retrieved on 2006-06-26.
- ↑ 3.0 3.1 Orchard, Anthony E. (ed.). "Proteaceae". Flora of Australia, Volume 16: Elaeagnaceae, Proteaceae 1. Melbourne: Australian Biological Resources Study / CSIRO Publishing. http://www.anbg.gov.au/abrs/online-resources/flora/stddisplay.xsql?pnid=1893.
- ↑ Pole M (1998). "The Proteaceae record in New Zealand". Australian Systematic Botany 11 (4): 343–372.
- ↑ Weston, P. H. and Crisp, M. D. (1996). "Trans-Pacific biogeographic patterns in the Proteaceae". in Keast, A. and Miller, S. E. (eds). The origin and evolution of Pacific Island Biotas, New Guinea to eastern Polynesia: Patterns and processes. Amsterdam: SPB Academic Publishing. pp. 215–232. ISBN 90-5103-136-X.
- ↑ L. A. S. Johnson and Briggs, B. G. (1975). "On the Proteaceae – the evolution and classification of a southern family". Journal of the Linnean Society of London. Botany 70: 83–182.
