Proteaceae

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 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. 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 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. 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. Due to these specialized proteoid roots, the Proteaceae are one of few flowering plant families which do not form symbioses with arbuscular mycorrhizal fungi.

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

  • Dryandra
  • Eidothea
  • Embothrium
  • Eucarpha
  • Euplassa
  • Faurea
  • Finschia
  • Floydia
  • Franklandia
  • Garnieria
  • Gevuina
  • Grevillea
  • Hakea
  • Helicia
  • Heliciopsis
  • Hicksbeachia
  • Hollandaea
  • Isopogon
  • Kermadecia
  • Knightia
  • Lambertia
  • Leucadendron
  • Leucospermum
  • Lomatia
  • Macadamia
  • Malagasia
  • Mimetes
  • Musgravea
  • Neorites
  • Opisthiolepis
  • Oreocallis
  • Orites
  • Orothamnus
  • Panopsis
  • Paranomus
  • Persoonia
  • Petrophile
  • Placospermum
  • Protea
  • Roupala
  • Serruria
  • Sleumerodendron
  • Sorocephalus
  • Spatalla
  • Sphalmium
  • Stenocarpus
  • Stirlingia
  • Strangea
  • Symphionema
  • Synaphea
  • Telopea
  • Toronia
  • Triunia
  • Turrillia
  • Vexatorella
  • Virotia
  • Xylomelum
  • Cultivation and 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 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 species are good examples of this: Lomatia ferruginea (Fuinque), Lomatia hirsuta (Radal) have been introduced in 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.

    Among banksias, which many of them 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 which 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 species, but smaller which is 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.

    References

    External links

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