| Proteaceae | |
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| Inflorescence ofProtea cynaroides | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Proteales |
| Family: | Proteaceae Juss.[2] |
| Genera | |
About 80, see text | |
TheProteaceae/ˌproʊtiˈeɪsiː/ form afamily offlowering plants predominantly distributed in theSouthern Hemisphere. The family comprises 83genera with about 1,660 knownspecies.[3]Australia andSouth Africa have the greatest concentrations of diversity. Together with thePlatanaceae (plane trees),Nelumbonaceae (the sacred lotus) and in the recentAPG IV system theSabiaceae, they make up the orderProteales. Well-known Proteaceae genera includeProtea,Banksia,Embothrium,Grevillea,Hakea, andMacadamia. Species such as the New South Wales waratah (Telopea speciosissima), king protea (Protea cynaroides), and various species ofBanksia,Grevillea, andLeucadendron are popularcut flowers. The nuts ofMacadamia integrifolia are widely grown commercially and consumed, as are those ofGevuina avellana on a smaller scale.
The name Proteaceae was adapted byRobert Brown from the name Proteae coined in 1789 for the family byAntoine Laurent de Jussieu, based on the genusProtea, which in 1767,Carl Linnaeus derived from the name of the Greek godProteus, a deity who was able to change between many forms.[4][5] This is an appropriate image, seeing as the family is known for its astonishing variety and diversity of flowers and leaves.[citation needed]
First described by French botanistAntoine Laurent de Jussieu, the family Proteaceae is a fairly large one, with around 80 genera, but less than 2,000 species. It is recognised by virtually alltaxonomists. Firmly established under classicalLinnaean taxonomy, it is also recognised by thecladistics-basedAPG andAPG II systems. It is placed in the orderProteales, whose placement has itself varied.
A classification of the genera within Proteaceae was made byLawrie Johnson andBarbara Briggs[6] in their influential 1975 monograph "On the Proteaceae: the evolution and classification of a southern family",[7] until it was largely superseded by the molecular studies of Peter H. Weston and Nigel Barker in 2006. Proteaceae are now divided into five subfamilies:Bellendenoideae,Persoonioideae,Symphionematoideae,Proteoideae andGrevilleoideae.[7] In 2008 Mast and colleagues updatedMacadamia and related genera in tribe Macadamieae. Furthermore,Orites megacarpus was found not to be within the genusOrites, nor in the tribe Roupaleae, instead in the tribe Macadamieae, hence given the new species nameNothorites megacarpus.[8] The full arrangement, according to Weston and Barker (2006) with the updates to genera from Mast et al. (2008), is as follows:
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The genera of Proteaceae are highly varied, withBanksia in particular providing a striking example ofadaptive radiation in plants.[9] This variability makes it impossible to provide a simple, diagnostic identification key for the family, although individual genera may be easily identified.
Plant stems with two types of radii, wide and multi-serrated or narrow and uni-serrated,phloem stratified or not, trilacunar nodes with threeleaf traces (rarely unilacunar with one trace),sclereids frequent;bark withlenticels frequently horizontally enlarged,cork cambium present, usually superficial.Roots lateral and short, often grouped in bundles (proteoid roots) with very dense root hairs, rarely withmycorrhiza.
Generally speaking, the diagnostic feature of Proteaceae is the compoundpseudanthium. In many genera, the most obvious feature is the large and often very showyinflorescences, consisting of many smallflowers densely packed into a compact head or spike. This character does not occur in all Proteaceae, however;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 thestyle-end that presents thepollen to the pollinator.[10]
Proteaceae flower parts occur in fours. The fourtepals are fused into a long, narrow tube with a closed cup at the top, and the filaments of the fourstamens 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 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, the perianth is split along one seam. The style continues to grow untilanthesis, when thenectaries begin to producenectar. 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.
Many of the Proteaceae have specialisedproteoid roots, masses of lateral roots and hairs forming a radial absorptive surface, produced in the leaf litter layer during seasonal growth, and usually shrivelling 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 exudingcarboxylates that mobilise previously unavailable phosphorus. They also increase the root's absorption surface, but this is a minor feature, as it also increases competition for nutrients against its own root clusters.[11] However, this adaptation leaves them highly vulnerable to dieback caused by thePhytophthora cinnamomiwater mould, and generally intolerant offertilization. Due to these specialized proteoid roots, the Proteaceae are one of few flowering plant families that do not form symbioses witharbuscular mycorrhizal fungi. They exude large amounts of organic acids (citric acid andmalic acid) every 2–3 days in order to aid the mobilization and absorption of phosphate. Many species are fire-adapted (pyrophytes), meaning they have strategies for surviving fires that sweep through their habitat. Some areresprouters, and have a thick rootstock buried in the ground that shoots up new stems after a fire, and others arereseeders, meaning 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 the chemicals in the smoke have now been shown to cause it.
There are four dioecious genera (Aulax,Dilobeia,Heliciopsis andLeucadendron), 11 andromonoecious genera and some other genera have species that are cryptically andromonoecious: two species are sterile and only reproduce vegetatively (Lomatia tasmanica,Hakea pulvinifera). The species vary between being autocompatible and autoincompatible, with intermediate situations; these situations sometimes occur in the same species. The flowers are usually protandrous. Just before anthesis, the anthers release theirpollen, 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 apollen-presenter, ensuring the nectar-feeders act as pollinators. The downside of this pollination strategy is that the probability of self-fertilisation is greatly increased; many Proteaceae counter this with strategies such asprotandry, self-incompatibility, or preferential abortion of selfed seed. The systems for presenting pollen are usually highly diverse, corresponding to the diversification of the pollinators.Pollination is carried out bybees,beetles,flies,moths, birds (honeyeaters,sunbirds,sugarbirds andhummingbirds) and mammals (rodents, smallmarsupials,elephant shrews andbats). The latter two means were evolutionarily derived fromentomophily in different, independent events. The dispersion of some species exhibitserotiny, which is associated with their pyrophytic behaviour. These trees accumulate fruits on their branches whose outer layers or protective structures (bracts) are highly lignified and resistant to fire. The fruit only release their seeds when they have been burnt and when the ground has been fertilized with ashes from the fire and is free from competitors. Many species have seeds withelaiosomes that are dispersed byants; the seeds with wings or thistledown exhibitanemochory, while the drupes and other fleshy fruit exhibitendozoochory as mammals and birds ingest them. Some African and Australian rodents are known to accumulate fruit and seeds of these plants in their nests in order to feed on them, although some manage to germinate.
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 andCentral America,India, eastern and south easternAsia, andOceania.[11] Only two species are known from New Zealand, although fossil pollen evidence suggests there were more previously.[12]
It is a good example of aGondwanan family, with taxa occurring on virtually every land mass considered a remnant of the ancientsupercontinent Gondwana, exceptAntarctica. The family and subfamilies are thought to have diversified well before the fragmentation of Gondwana, implying all of them are well over 90 million years old. Evidence for this includes an abundance of proteaceouspollen found in theCretaceouscoal deposits of theSouth Island ofNew Zealand. It is thought to have achieved its present distribution largely bycontinental drift rather than dispersal across ocean gaps.[13]
No conclusive studies have been carried out on the chemical substances present in this broad family. The generaProtea andFaurea are unusual as they usexylose as the main sugar in their nectar and as they have high concentrations of polygalactol, whilesucrose is the main sugar present inGrevillea.Cyanogenic glycosides, derived fromtyrosine, are often present, as areproanthocyanidines (delphinidin andcyanidin),flavonols (kaempferol,quercetin andmyricetin) andarbutin.Alkaloids are usually absent.Iridoids andellagic acid are also absent.Saponins andsapogenins can be either present or absent in different species. Many species accumulatealuminium.
Many traditional cultures have used Proteaceae as sustenance, medicine, for curing animal hides, as a source of dyes, firewood and as wood for construction. Aboriginal Australians eat the fruit ofPersoonia, and the seeds of species from other genera, includingGevuina andMacadamia, form part of the diet of the indigenous peoples but are also sold throughout the world. The tender shoots ofHelicia species are used in Java, and the nectar from the inflorescences of a number of species is drunk in Australia. Traditional medicines can be obtained from infusions of the roots, bark, leaves, or flowers of many species that are used as topical applications for skin conditions or internally as tonics, aphrodisiacs, and galactogens to treat headaches, cough, dysentery, diarrhea, indigestion, stomach ulcers, and kidney disease. The wood from the trees of this family is widely used in construction and for internal uses such as decoration; the wood from species ofProtea,Leucadendron andGrevillea is especially popular. Manyspecies are used in gardening, particularly genera ofBanksia,Embothrium,Grevillea, andTelopea. This use has resulted in the introduction of exotic species that have become invasive; examples include the hakea willow (Hakea salicifolia) and the silky hakea (Hakea sericea) in Portugal.
Two species ofMacadamia are cultivated commercially for their edible nuts.Gevuina avellana (Chilean hazel) is also cultivated for its edible nuts, inChile andNew Zealand, and they are also used in the pharmaceutical industry for their humectant properties and as an ingredient insunscreens. It is the most cold-resistant of the tree families that produce nuts.[citation needed] It is also planted in theBritish Isles and on the Pacific coast of theUnited States for its tropical appearance and its ability to grow incooler climates.
Many Proteaceae species are cultivated by thenursery industry as barrier plants and for their prominent and distinctive flowers and foliage. Some species are of importance to thecut flower industry, especially someBanksia andProtea species.
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 offynbos, which forms part of theCape 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 theEricaceae and theRestionaceae. 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 inwildlife gardens for attracting birds and useful insects.
The species most valued as ornamentals are the trees that grow in southern latitudes as they give landscapes intemperate climates a tropical appearance;Lomatia ferruginea (Fuinque),Lomatia hirsuta (Radal) have been introduced in WesternEurope and to the westernUnited States.Embothrium coccineum (Chilean Firetree orNotro) is highly valued in the British Isles for its dark red flowers and can be found as far north as theFaroe Islands at a latitude of 62° north.
Among thebanksias, many of which grow in temperate and Mediterranean climates, the vast majority are shrubs; only a few are trees that are valued for their height. Among the tallest species are:B. integrifolia with its subspeciesB. integrifolia subsp.monticola, which is noteworthy as the plants that form the subspecies are the tallest trees of the banksias and they are more frost-resistant than other banksias,B. seminuda,B. littoralis,B. serrata; among those that can be considered small trees or large shrubs:B. grandis,B. prionotes,B. marginata,B. coccinea andB. speciosa; all of these are planted in parks and gardens and even along roadsides because of their size. The rest of the species of this genus, around 170 species, are shrubs, although some of them are valued for their flowers.
Another species that is cultivated in some parts of the world, although it is smaller, isTelopea speciosissima (Waratah), from the mountains ofNew South Wales,Australia.
Some temperate climate species are cultivated more locally in Australia for their attractive appearance:Persoonia pinifolia (pine-leavedgeebung) is valued for its vivid yellow flowers and grape-like fruit.Adenanthos sericeus (woolly bush) is planted for its attractive soft leaves and its small red or orange flowers.Hicksbeachia pinnatifolia (beef nut, red bauple nut) is commonly planted for its foliage and edible nuts.
The Proteaceae are particularly susceptible to certain parasites, in particular theoomycetePhytophthora cinnamomi, which causes severe root rot in the plants that grow in Mediterranean climates.Fusarium oxysporum causes a disease called fusariosis in roots that causes a yellowing and wilting, with serious ecological damages to woodland plants and economic losses in plants of commercial interest. Other common infections are caused by species ofBotryosphaeria,Rhizoctonia,Armillaria,Botrytis,Calonectria and other fungi.
TheIUCN[14] considers that 47 Proteaceae species are threatened, of which one species,Stenocarpus dumbeensisGuillaumin, 1935, from New Caledonia, is thought to be extinct. The species of this family are particularly susceptible to the destruction or fragmentation of theirhabitat, fire, parasitic diseases,competition from introduced plants,soil degradation and other damage provoked by humans and their domesticated animals. The species are also affected byclimate change.
The Proteaceae have a rich fossil record, despite the inherent difficulties in identifying remains that do not show diagnostic characteristics. Identification usually comes from using a combination of brachy-paracytic stomata and the unusualtrichome bases or, in other cases, the unusual structure of pollen tetrads.[citation needed]Xylocaryon was identified as a member of the Proteaceae from the similarity of its fruit to the extant genusEidothea.[15] Fossils attributable to this family have been found on the majority of areas that formed theGondwana supercontinent. A wide variety of pollen belonging to this family dating back to the UpperCretaceous (Campanian-Maastrichtian) from the south east of Australia and pollen from the Middle Cretaceous (Cenomanian-Turonian) from northern Africa and Peru described asTriorites africaensis. The first macrofossils appear twenty million years later in thePalaeocene of South America and the north east of Australia. The fossil record of some areas, such as New Zealand and Tasmania, show a greater biodiversity for Proteaceae than currently exists, which supports the fact that the distribution of many taxa has changed drastically with the passage of time and that the family has suffered a general decline, including high levels of extinction during theCenozoic.[citation needed]
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