Utente:Esculapio/Sandbox/Banksia
Tassonomia
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Il genere Banksia fu descritto per la prima volta e così denominato da Carlo Linneo il Giovane nella sua pubblicazione dell'aprile del 1782 Supplementum Plantarum. Il nome del genere fu scelto in onore del botanico inglese Sir Joseph Banks, che raccolse i primi campioni Banksia nel 1770, durante la prima spedizione di James Cook.
Il genere Banksia appartiene alla famiglia Proteaceae, sottofamiglia Grevilleoideae, tribù Banksieae, e comprende circa 170 specie.
Classical taxonomic treatment
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In 1981, Alex George published his classic 1981 monograph The Genus Banksia L.f. (Proteaceae). George's arrangement was based on a variety of properties including leaf, style, pollen-presenter, follicle and seed characters, with the criterion that a taxon was considered a distinct species only if it exhibited a "significant and consistent difference in the morphology of flowers and/or fruit".[1] It was the first thorough revision of the taxonomy of Banksia for over a century, and formed the basis for George's 1984 The Banksia Book,[2] which remains the standard text on the genus, and the treatment of Banksia in the Flora of Australia series.[3]
George followed Brown in dividing Banksia into two subgenera, Banksia and Isostylis. He then divided subgenus Banksia into two sections: Banksia for species with straight or slightly curved styles, and Oncostylis for species with hooked styles.[1] These two sections were then divided into nine and three series respectively. The arrangement into series largely followed Bentham, with series Orthostylis remaining somewhat heterogeneous, and Cyrtostylis remaining highly heterogeneous.[4]
This conventional taxonomic arrangement of Banksia, as provided by George and published in the Flora of Australia series, may be summarised as follows:
- Genus Banksia
- Subgenus Banksia
- Section Banksia
- Series Salicinae
- Series Grandes
- Series Banksia
- Series Crocinae
- Series Prostratae
- Series Cyrtostylis
- B. media – B. praemorsa – B. epica – B. pilostylis – B. attenuata – B. ashbyi – B. benthamiana – B. audax – B. lullfitzii – B. elderiana – B. laevigata – B. elegans – B. lindleyana
- Series Tetragonae
- Series Bauerinae
- Series Quercinae
- Section Coccinea
- Section Oncostylis
- Series Spicigerae
- Series Tricuspidae
- Series Dryandroidae
- Series Abietinae
- Section Banksia
- Subgenus Isostylis
- Subgenus Banksia
Cladistic analyses
[modifica | modifica wikitesto]Thiele and Ladiges
[modifica | modifica wikitesto]In 1996, Kevin Thiele and Pauline Ladiges published a cladistic analysis of the Banksia genus in the journal Australian Systematic Botany.[4] As their cladogram differed substantially from the current taxonomic arrangement, they published a revised arrangement that accorded better with their results. Four varieties were promoted to species rank: B. conferta var. penicillata to B. penicillata (now B. conferta subsp. penicillata); B. gardneri var. brevidentata to B. brevidentata; B. gardneri var. hiemalis to B. hiemalis; and B. sphaerocarpa var. dolichostyla to B. dolichostyla. Two new series and eleven subseries were introduced; Banksia sect. Oncostylis and Banksia ser. Crocinae were discarded; and Banksia ser. Cyrtostylis was largely redefined. Six species were left incertae sedis.[4]
Most aspects of Thiele and Ladiges' arrangement were not accepted by George in his 1999 revision. He stated that "the infrageneric classification and systematic sequence presented here are modified from that of George (1981) and take into account new data revealed in the work of Thiele & Ladiges (1996)", but none of the four promotions to species rank was accepted, and none of the thirteen infrageneric taxa introduced by Thiele and Ladiges was retained.[3] However, a number of Australian herbaria have continued to follow Thiele and Ladiges on some points, for example by recognising the four species that they promoted.[5]
DNA analysis
[modifica | modifica wikitesto]Following on from an earlier molecular study,[6] Austin Mast and co-authors published cladistic analyses of genetic data from DNA samples of almost all species of Banksia, along with five Dryandra species, in 2002 and 2005. Their results indicated the presence of two large clades of Banksia, which they named "/Cryptostomata" ("hidden stomates") and "/Phanerostomata" ("visible stomates").
The /Phanerostomata were defined as those taxa in which the leaf stomata occur superficially or in shallow pits. These taxa are typically tall shrubs and trees that occur in moist areas; they have unbeaked follicles and soft, short-lived leaves that are in many cases needle-like. The clade includes all eastern taxa of the series Salicinae and Spicigerae (that is, all taxa except B. serrata, B. aemula and B. ornata) and also the western Spicigerae, Quercinae, Grandes, Abietinae and Dryandroideae.
The /Cryptostomata were defined as those taxa in which the leaf stomata occur in crypts with constricted entrances. These are usually small shrubs that occur on dry, infertile sandplains. They have beaked follicles and thick, tough, long-lived serrated leaves. It includes all other western taxa, plus the eastern species B. serrata, B. aemula and B. ornata, and also appears to include Dryandra. It is worth noting that Dryandra does not appear especially closely related to the Isostylis group, which is instead most closely related to B. elegans and then B. attenuata.
Thus, the results presented by Mast et al. strongly suggest that Banksia is paraphyletic with respect to Dryandra. Although they did not propose a new taxonomic arrangement, they did consider various options for adjusting the current accepted arrangement to remove the polyphyly. They conclude that the simplest and least disruptive solution would be to merge Dryandra into Banksia.[7][8] This solution was put into effect in a subdequent paper by Mast & Thiele.[9]
The change has been adopted by a number of Australian herbaria including the Western Australian Herbarium, now headed by Thiele (this has the largest holdings of specimens), and by the Australian Plant Census, a project of the Council of Heads of Australasian Herbaria. This is in accordance with majority current taxonomic practice, in which only monophyletic groups are named as taxa, and groups found to be non-monophyletic (e.g. Banksia not including Dryandra) are adjusted to achieve a monophyletic naming system. Alex George maintains a firm position against the change, arguing variously that the phylogenetic analyses sono fallaci and that paraphyly does not necessitate taxonomic changes.[10]
Note
[modifica | modifica wikitesto]- ^ a b (EN) George A.S., The genus Banksia L.f. (Proteaceae), in Nuytsia, vol. 3, n. 3, 1981, pp. 239–473 [426–29], ISSN 0085-4417.
- ^ Alex George, The Banksia Book, Kangaroo Press and The Society for Growing Australian Plants (NSW Region), 1996, ISBN 0-86417-818-2.
- ^ a b Alex S. George, Banksia, in Wilson, Annette (ed.) (a cura di), Flora of Australia, Volume 17B: Proteaceae 3: Hakea to Dryandra, Collingwood, Victoria, CSIRO Publishing / Australian Biological Resources Study, 1999, pp. 175–251, ISBN 0-643-06454-0.
- ^ a b c Thiele, Kevin and Pauline Y. Ladiges, A Cladistic Analysis of Banksia (Proteaceae) (PDF), in Australian Systematic Botany, vol. 9, n. 5, 1996, pp. 661–733, DOI:10.1071/SB9960661. URL consultato il 10 gennaio 2007.
- ^ Peter Olde, One new Banksia and two new Grevillea species (Proteaceae: Grevilleoideae) from Western Australia (PDF), in Nuytsia, vol. 15, n. 1, 2002, pp. 85–99. URL consultato il 10 gennaio 2007.
- ^ Mast AR. (1998) Molecular systematics of subtribe Banksiinae (Banksia and Dryandra; Proteaceae) based on cpDNA and nrDNA sequence data: implications for taxonomy and biogeography. Australian Systematic Botany 11: 321–342
- ^ Austin R. Mast, Historical Biogeography and the Origin of Stomatal Distributions in Banksia & Dryandra (Proteaceae) Based on Their cpDNA Phylogeny, in American Journal of Botany, vol. 89, n. 8, August 2002, pp. 1311–1323, DOI:10.3732/ajb.89.8.1311. URL consultato il 2 luglio 2006.
- ^ Mast, Austin R., Eric H. Jones and Shawn P. Havery, An Assessment of Old and New DNA sequence evidence for the Paraphyly of Banksia with respect to Dryandra (Proteaceae), in Australian Systematic Botany, vol. 18, n. 1, CSIRO Publishing / Australian Systematic Botany Society, 2005, pp. 75–88, DOI:10.1071/SB04015.
- ^ Austin R. Mast, The transfer of Dryandra R.Br. to Banksia L.f. (Proteaceae), in Australian Systematic Botany, vol. 20, n. 1, February 2007, pp. 63–71, DOI:10.1071/SB06016.
- ^ George, Alex, You don't have to call Dryandra Banksia, in Australian Plants Online: ANPSA website, Australian Native Plants Society (Australia), 2008. URL consultato il 16 dicembre 2009.