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. Well known genera include Protea, Banksia, Embothrium, Grevillea, Hakea, Dryandra and Macadamia. Species such as the New South Wales Waratah (Telopea speciosissima), King Protea (Protea cynaroides), and various species of Banksia, Grevillea, and Leucadendron are popular cut flowers, while the nuts of Macadamia integrifolia are widely commercially grown and consumed.
Many genera of 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 that 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.
Generally speaking, the diagnostic feature of Proteaceae is the unusual flower. Proteaceae flower parts occur in fours, but the four tepals are fused into a long narrow tube with a closed cup at the top, and the filaments of the four stamens are fused to the tepals, in such a way that the anthers are enclosed within the cup. The pistil initially passes along the inside of the perianth tube, so that the stigma too is enclosed within the cup. As the flower develops, the pistil grows rapidly. Since the stigma is trapped, the style must bend to elongate, and eventually it bends so far that it splits the perianth along one seam. The style continues to grow until anthesis, when the nectaries begin to produce nectar. At this time, the perianth splits into its component tepals, the cup splits apart, and the pistil is released to spring more or less upright.
Just before anthesis, the anthers release their pollen, depositing it onto the stigma, which in many cases has an enlarged fleshy area specifically for the deposition of its own pollen. Nectar-feeders are unlikely to come into contact with the anthers themselves, but can hardly avoid contacting the stigma; thus the stigma functions as a pollen-presenter, ensuring that nectar-feeders act as pollinators. The down side of this pollination strategy is that the probability of self-fertilisation is greatly increased; many Proteaceae counter this with strategies such as protandry, self-incompatibility, or preferential abortion of selfed seed.
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. Only two species are known from New Zealand although fossil pollen evidence suggests there were more previously.
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.
Many of the Proteaceae have specialised proteoid roots. Proteoid roots are masses of lateral roots and hairs forming a radial absorptive suface, produced in the leaf litter layer during seasonal growth, and usually shriveling at the end of the growth season. They are an adaptation to growth in poor phosphorus deficient soils, greatly increasing the plants access to scarce water and nutrients by exuding carboxylates that mobilise previously unavailable phoshorus. They also increasing the root's absorption surface but this is a minor feature as it also increases competition for nutrients against its own root clusters. 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 that do not form symbioses with arbuscular mycorrhizal fungi.
Because of their large inflorescences, the Proteaceae are highly attractive to both a large variety of insects, their attendant predators such as birds and lizards, and nectarivorous birds such as sugarbirds, sunbirds and honeyeaters. Some produce berries, attracting further bird species.
Many species are fire-adapted, meaning that they have strategies for surviving fires that sweep through their habitat. Some are resprouters, and have a thick rootstock buried in the ground that shoots up new stems after a fire, and others are reseeders, meaning that the adult plants are killed by the fire but disperse their seeds, which are stimulated by the smoke to take root and grow. The heat was previously thought to have stimulated growth but it has now been found that it is in fact the chemicals in the smoke.
First described by French botanist Antoine Laurent de Jussieu, the Proteaceae family is a fairly large one, with around eighty genera, but less than two thousand species. 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 by L. A. S. Johnson and Barbara Briggs in their influential 1975 monograph "On the Proteaceae: the evolution and classification of a southern family". Their classification has been refined somewhat over the ensuing three decades, most notably by Peter Weston and Nigel Barker in 2006. Proteaceae is now divided into five subfamilies: Bellendenoideae, Persoonioideae, Symphionematoideae, Proteoideae and Grevilleoideae. The full arrangement, according to Weston and Barker, is as follows:
Toronia — Garnieria — Acidonia — Persoonia
Agastachys — Symphionema
Eidothea — Beauprea — Beaupreopsis — Dilobeia — Cenarrhenes — Franklandia
Conospermum — Synaphea
Petrophile — Aulax
Protea — Faurea
Leucadendron — Serruria — Paranomus — Vexatorella — Sorocephalus — Spatalla — Leucospermum — Mimetes — Diastella — Orothamnus
Sphalmium — Carnarvonia
Megahertzia — Knightia — Eucarpha — Triunia
Roupala — Neorites — Orites
Lambertia — Xylomelum
Helicia — Hollandaea
Darlingia — Floydia
Musgravea — Austromuellera
Banksia — Dryandra
Embothrium — Oreocallis — Alloxylon — Telopea
Stenocarpus — Strangea
Opisthiolepis — Buckinghamia — Hakea — Grevillea — Finschia
Macadamia — Panopsis — Brabejum
Malagasia — Catalepidia
Virotia — Athertonia — Heliciopsis
Cardwellia — Sleumerodendron — Euplassa — Gevuina — Bleasdalea — Hicksbeachia — Kermadecia — Turrillia
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 hazelnut) 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.
The most valuable species as ornamental are the southernmost trees because they can give to landscapes an exotic tropical appearance in temperate climates; the following Chilean-Argentinian species are good examples of this: Lomatia ferruginea (Fuinque), Lomatia hirsuta (Radal) have been introduced to Western Europe and Western United States. Embothrium coccineum (Chilean firetree or Notro) is very valued because of its deep red flowers in the British Isles and is found as north as Faroe Islands at 62° North Latitude.
Sugarbushes (Protea), pincushions (Leucospermum) and conebushes (Leucadendron), as well as others like pagodas (Mimetes), Aulax and blushing brides (Serruria), comprise one of the three main plant groups of fynbos, which forms part of the Cape Floral Kingdom, the smallest but richest plant kingdom for its size and the only kingdom contained within a single country. The other main groups of plants in fynbos are the Ericaceae and the Restionaceae. South African proteas are thus widely cultivated due to their many varied forms and unusual flowers. They are popular in South Africa for their beauty and their usefulness in the wildlife garden for attracting birds and useful insects.
Among banksias, many of which grow in Mediterranean and maritime climates, the huge majority of them are shrubs, only few reach tree sizes and they are appreciated because of their height and among taller species are outstanding: B. integrifolia with its subspecies B. integrifolia subsp. monticola is remarkable for having the tallest banksia trees and for withstanding more frosts than all banksias, B. seminuda, B. littoralis, B. serrata; those that can be considered little trees or big shrubs: B. grandis , B. prionotes, B. marginata, B. coccinea and B. speciosa, and are planted in parks, gardens and even streets, the rest of species of this genus consisting of around 170 are only shrubs, even some of them are valued because of their flowers.
Another, smaller species grown in several parts of the world is Telopea speciosissima (Waratah), from the mountains of New South Wales, Australia. Some species in temperate climates are cultivated more locally in Australia because of their beauty: Persoonia pinifolia (Pine-leaved Geebung) is very appreciated for its vivid yellow flowers and its grape-like fruits. Adenanthos sericeus (Woolly Bush) is planted for its showy soft leaves and its little, and red or orange flowers. Hicksbeachia pinnatifolia (red bauple nut) is commonly planted for its foliage and edible nuts.
1. ^ 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. doi:10.3732/ajb.89.8.1311. ISSN 0002-9122.
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