Banksia subg. Isostylis

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Banksia subg. Isostylis
Banksia ilicifolia marchetti latebud2 email.jpg
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Proteales
Family: Proteaceae
Genus: Banksia
Subgenus: Banksia subg. Isostylis
R.Br.
Species

Banksia subg. Isostylis is a subgenus of Banksia . It contains three closely related species, all of which occur only in Southwest Western Australia. Members of subgenus Isostylis have dome-shaped flower heads that are superficially similar to those of B. ser. Dryandra, but structurally more like reduced versions of the "flower spikes" characteristic of most other Banksia taxa.

Contents

There are three species of Banksia subg. Isostylis, B. ilicifolia (holly-leaved banksia), B. cuneata (matchstick banksia) and B. oligantha (Wagin banksia). B. ilicifolia is widely distributed and relatively common, but the other two species are rare and threatened.

Description

Banksia subg. Isostylis shares with B. ser. Dryandra the property of having compact, dome-shaped flower heads. Structurally, however, Isostylis flower heads are quite different from those of B. ser. Dryandra, having more in common with the erect flower spikes of other Banksia taxa. Specifically, Isostylis flower heads have an ovoid axis, suggestive of a greatly reduced flower spike, whereas Dryandra flower heads emerge from a flat receptable. Furthermore, Isostylis has thick follicles with a woolly coating, whereas Dryandra follicles are thin and hairless; and the involucral, common and floral bracts of Isostylis are unlike those of Dryandra. [1]

The Isostylis species are all upright shrubs or trees, with a single trunk. They generally have serrate leaves, although in rare cases B. ilicifolia may have entire leaves. [2]

Taxonomy

Taxonomic history

Branch of B. cuneata B cuneata gnangarra 28.JPG
Branch of B. cuneata

Banksia subg. Isostylis was first published by Robert Brown in his 1810 Prodromus Florae Novae Hollandiae et Insulae Van Diemen ; thus its full name, with author citation, is Banksia subg. Isostylis R.Br. [3] Brown's arrangement was the first infrageneric arrangement of Banksia, making B. subg. IsostylisBanksia's first infrageneric taxon. [4] Brown erected B. subg. Isostylis to contain B. ilicifolia, which was then the only known Banksia with a dome-shaped inflorescence. He did not explicitly name a type species for the subgenus, [4] but B. ilicifolia is treated as the type because it was the only member when the subgenus was published. [1]

Twenty years later, Brown issued a supplement to his Prodromus entitled Supplementum Primum Prodromi Florae Novae Hollandiae ; another nine Banksia species were published, but there was no change to the 1810 arrangement, and no new Isostylis species. [5]

In 1846, Édouard Spach promoted B. subg. Isostylis to genus rank in his Histoire Naturelle des Vegetaux: Phanerogames . This was not accepted, and Isostylis (R.Br.) Spach is now considered a nomenclatural synonym of B. subg. Isostylis. [6]

When Carl Meissner published his arrangement of Banksia in 1856, he demoted both of Brown's subgenera to sectional rank, maintaining B. sect. Isostylis (R.Br.) Meisn. as a monospecific taxon containing only B. ilicifolia. Meissner's rank and circumscription of Isostylis was retained by George Bentham in his 1870 arrangement for Flora Australiensis , but Bentham also published a putative variety of B. ilicifolia, B. i. var. integrifolia, based on specimens collected by Ludwig Preiss near the Swan River in Western Australia. This was later overturned.

In 1905, James Britten challenged the genus name Banksia, on the grounds that Banksia J.R.Forst & G.Forst had precedent over Banksia L.f. Britten adopted the name Isostylis for the entire genus, republishing the names Isostylis dentata (L.f.) Britten for B. dentata (Tropical Banksia), Isostylis ericifolia (L.f.) Britten for B. ericifolia (Heath-leaved Banksia), Isostylis integrifolia (L.f.) Britten for B. integrifolia (Coast Banksia) and Isostylis serrata (L.f.) Britten for B. serrata (Saw Banksia). This challenge failed, Banksia L.f. was eventually conserved, and his four names are now considered taxonomic synonyms of their respective names under Banksia L.f. None of them are considered members of Isostylis.

The next change to Isostylis came in 1981, when Alex George promoted it back to subgenus rank, and published a second species, B. cuneata . In discussing the subgenus, George commented that there had been calls to transfer Isostylis into Dryandra , which was then a distinct genus. He argued, however, that the similarities between Isostylis and Dryandra were largely superficial, whereas the similarities with Banksia were much more important taxonomically. His conclusion was that the taxon should remain in Banksia, although he did not rule out promoting it into a separate genus. A third B. subg. Isostylis species, B. oligantha , was published by George in 1988.

In 1996, Kevin Thiele and Pauline Ladiges published a revised arrangement based on a cladistic analysis of morphological characters of Banksia. They took up the question of an affinity of Isostylis with Dryandra, finding George's arguments unconvincing but failing to find any further evidence for or against Isostylis's placement within Banksia. They eventually accepted both of George's subgenera, using each as an outgroup in the analysis of the other. Thus their analysis yielded no information about the circumscription and placement of Isostylis, and their arrangement maintained Isostylis as a subgenus. [7]

Thiele and Ladiges' arrangement was not accepted by George, and was largely discarded by him in his 1999 arrangement. The placement and circumscription of B. subg. Isostylis was unaffected and can be summarised as follows: [2]

B. cuneata grows as a large shrub, up to three metres in height. B cuneata gnangarra 25.JPG
B. cuneata grows as a large shrub, up to three metres in height.
Banksia
B. subg. Banksia (3 sections, 11 series, 73 species, 11 subspecies, 14 varieties)
B. subg. Isostylis
B. ilicifolia
B. oligantha
B. cuneata

Since 1998, Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae. His analyses has provided compelling evidence for the paraphyly of Banksia with respect to Dryandra, and suggest an overall phylogeny that is very greatly different from George's arrangement. Mast's results clearly recognise Isostylis as a distinct clade, but place it in a fairly recent position, within a clade that also contains B. elegans (Elegant Banksia) and B. attenuata (Candlestick Banksia). It falls a substantial distance from Dryandra, suggesting that similarities between those two groups are indeed superficial. [8] [9] [10]

Early in 2007, Mast and Thiele initiated a rearrangement of Banksia by merging Dryandra into it, and publishing B. subg. Spathulatae for the species having spoon-shaped cotyledons. They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, B. subg. Isostylis has been set aside. If maintained at all in Mast and Thiele's forthcoming arrangement, it will be at a lesser rank than subgenus. [11]

Relationships within B. subg. Isostylis still remain unclear. Though Mast's studies found B. cuneata to be the most basal of the three species, [9] a 2004 study of genetic divergence within the subgenus yielded both other possibilities: some analyses suggested B. ilicifolia as basal, while others suggested B. oligantha. Further complicating the situation is the existence of a population of B. cuneata having both genetic and phenetic affinities with B. oligantha. The origin of this population is unknown. It might have arisen through hybridisation, or it may be a transitional or even ancestral form. Finally, biogeographical factors suggest that B. ilicifolia would be the most basal of the three species: it occurs in the High Rainfall Zone where relictual species are most common, whereas the others are restricted to the Transitional Rainfall Zone, where more recently evolved species are most common. [12]

Distribution

Distribution of the three B. subg.Isostylis species: B. ilicifolia (red), B. cuneata (green), and B. oligantha (blue) Banksia subg. Isostylis map.png
Distribution of the three B. subg.Isostylis species: B. ilicifolia (red), B. cuneata (green), and B. oligantha (blue)

Species of B. subg. Isostylis occur only in Western Australia's South West Botanical Province. B. ilicifolia is widespread within 70 kilometres of the coast from Mount Lesueur in the north, south to Cape Leeuwin and east to Albany. The other two species occur further inland, and have quite limited distributions. B. cuneata occurs Brookton and Bruce Rock in the Avon Wheatbelt biogeographic region; while B. oligantha occurs slightly further south, in the vicinity of Wagin. [2] [13]

Ecology

Ecologically, B. subg. Isostylis is similar to other Banksias. As with other Banksia taxa, all three species have proteoid roots, roots with dense clusters of short lateral rootlets that form a mat in the soil just below the leaf litter. These roots are particularly efficient at absorbing nutrients from nutrient-poor soils, such as the phosphorus-deficient native soils of Australia. They lack a lignotuber, so shrubs are killed by bushfire; mature trees of B. ilicifolia have a limited ability to resprout from epicormic buds on the trunk. [1] But like all Banksias they release their aerial seed bank following a bushfire. This adaptation, known as serotiny, ensures the rapid regeneration of populations killed by fire.

B. cuneata and B. oligantha have been declared rare under both Western Australia's Wildlife Conservation Act 1950, and the federal Environment Protection and Biodiversity Conservation Act 1999. Threats include loss of habitat, Phytophthora cinnamomi dieback, and grazing on seedlings by feral rabbits. [14] [15]

Cultivation

None of the B. subg. Isostylis species are popular in cultivation. The two rare species are virtually unknown in cultivation. B. ilicifolia is better known, but its usefulness as an amenity plant is limited by the fact that it has very prickly leaves. [16]

Related Research Articles

<i>Banksia <span style="font-style:normal;">subg.</span> Banksia</i> Subgenus in the family Proteaceae

Banksia subg. Banksia is a valid botanic name for a subgenus of Banksia. As an autonym, it necessarily contains the type species of Banksia, B. serrata. Within this constraint, however, there have been various circumscriptions.

<i>Banksia ilicifolia</i> Tree in the family Proteaceae endemic to southwest Western Australia

Banksia ilicifolia, commonly known as holly-leaved banksia, is a tree in the family Proteaceae. Endemic to southwest Western Australia, it belongs to Banksia subg. Isostylis, a subgenus of three closely related Banksia species with inflorescences that are dome-shaped heads rather than characteristic Banksia flower spikes. It is generally a tree up to 10 metres (33 ft) tall with a columnar or irregular habit. Both the scientific and common names arise from the similarity of its foliage to that of the English holly Ilex aquifolium; the glossy green leaves generally have very prickly serrated margins, although some plants lack toothed leaves. The inflorescences are initially yellow but become red-tinged with maturity; this acts as a signal to alert birds that the flowers have opened and nectar is available.

<i>Banksia cuneata</i> Endangered species of flowering plant

Banksia cuneata, commonly known as matchstick banksia or Quairading banksia, is an endangered species of flowering plant in the family Proteaceae. Endemic to southwest Western Australia, it belongs to Banksia subg. Isostylis, a sub-genus of three closely related Banksia species with inflorescences or flower clusters that are dome-shaped heads rather than characteristic Banksia flower spikes. A shrub or small tree up to 5 m (16 ft) high, it has prickly foliage and pink and cream flowers. The common name Matchstick Banksia arises from the blooms in late bud, the individual buds of which resemble matchsticks. The species is pollinated by honeyeaters (Meliphagidae).

Banksia oligantha, commonly known as Wagin banksia, is an endangered species in the plant family Proteaceae endemic to south west Western Australia. It belongs to Banksia subg. Isostylis, a subgenus of three closely related Banksia species with dome-shaped heads as inflorescences, rather than characteristic Banksia flower spikes. A shrub or small tree up to 4 m (13 ft) high, it has prickly foliage and pink and cream flowerheads which appear in late Spring.

Taxonomy of <i>Banksia</i>

As with other flowering plants, the taxonomy of Banksia has traditionally been based on anatomical and morphological properties of the Banksia flower, fruiting structure and seed, along with secondary characteristics such as leaf structure and growth habit. Increasingly, molecular evidence from DNA is providing important new insights into relationships within the genus and between this and other genera in the Proteaceae.

<i>Banksia dryandroides</i> Species of shrub in the family Proteaceae from the south coast of Western Australia

Banksia dryandroides, the dryandra-leaved banksia, is a species of small shrub in the plant genus Banksia. The Noongar peoples know the tree as manyat. It occurs in shrubland, woodland and kwongan on the south coast of Western Australia between Narrikup and Beaufort Inlet. The species is placed alone in series B. ser. Dryandroideae.

<i>Banksia elegans</i> Species of shrub in the family Proteaceae endemic to Western Australia

Banksia elegans, commonly known as the elegant banksia, is a species of woody shrub that is endemic to a relatively small area of Western Australia. Reaching 4 m (13 ft) high, it is a suckering shrub that rarely reproduces by seed. The round to oval yellow flower spikes appear in spring and summer. Swiss botanist Carl Meissner described Banksia elegans in 1856. It is most closely related to the three species in the subgenus Isostylis.

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Dryandra subg. Diplophragma is an obsolete subgenus within the former genus Dryandra. It was first published by Robert Brown in 1830, but was discarded by George Bentham in 1870. It was reinstated with a new circumscription by Alex George in 1996, but was ultimately discarded again in 2007 when Austin Mast and Kevin Thiele sunk Dryandra into Banksia.

Robert Brown's taxonomic arrangement of Banksia was published in his book of 1810, Prodromus Florae Novae Hollandiae et Insulae Van Diemen, and expanded in the supplement to that publication, Supplementum Primum Prodromi Florae Novae Hollandiae, in 1830. It was the first survey of Banksia species to be published, and included descriptions of a number of previously undescribed species.

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References

  1. 1 2 3 George, Alex S. (1981). "The Genus Banksia L.f. (Proteaceae)". Nuytsia . 3 (3): 239–473.
  2. 1 2 3 George, A. S. (1999). "Banksia". In Wilson, Annette (ed.). Flora of Australia. Vol. 17B. CSIRO Publishing / Australian Biological Resources Study. pp. 175–251. ISBN   0-643-06454-0.
  3. "Banksia subgen. Isostylis R.Br". Australian Plant Name Index (APNI), IBIS database. Centre for Plant Biodiversity Research, Australian Government.
  4. 1 2 Brown, Robert (1810). Prodromus Florae Novae Hollandiae et Insulae Van Diemen. London: Taylor.
  5. Brown, Robert (1830). Supplementum Primum Prodromi Florae Novae Hollandiae. London: Taylor.
  6. "Isostylis (R.Br.) Spach". Australian Plant Name Index (APNI), IBIS database. Centre for Plant Biodiversity Research, Australian Government.
  7. Thiele, Kevin; Ladiges, Pauline Y. (1996). "A Cladistic Analysis of Banksia (Proteaceae)". Australian Systematic Botany. 9 (5): 661–733. doi:10.1071/SB9960661.
  8. Mast, Austin R. (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 (4): 321–342. doi:10.1071/SB97026.
  9. 1 2 Mast, Austin; Thomas J. Givnish (2002). "Historical biogeography and the origin of stomatal distributions in Banksia and 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. PMID   21665734.
  10. Mast, Austin R.; Eric H. Jones & Shawn P. Havery (2005). "An assessment of old and new DNA sequence evidence for the paraphyly of Banksia with respect to Dryandra (Proteaceae)". Australian Systematic Botany . CSIRO Publishing / Australian Systematic Botany Society. 18 (1): 75–88. doi:10.1071/SB04015.
  11. Mast, Austin R.; Thiele, Kevin (2007). "The transfer of Dryandra R.Br. to Banksia L.f. (Proteaceae)". Australian Systematic Botany . 20 (1): 63–71. doi:10.1071/SB06016.
  12. Broadhurst, Linda M.; Coates, David J. (2004). "Genetic divergence among and diversity within two rare Banksia species and their common close relative in the subgenus Isostylis R.Br. (Proteaceae)". Conservation Genetics. 5 (6): 837–846. doi:10.1007/s10592-004-5268-9. S2CID   39559876.
  13. Taylor, Anne; Hopper, Stephen (1988). The Banksia Atlas (Australian Flora and Fauna Series Number 8). Canberra: Australian Government Publishing Service. ISBN   0-644-07124-9.
  14. Banksia cuneata — Matchstick Banksia, Quairading Banksia , Species Profile and Threats Database , Department of the Environment and Heritage, Australia.
  15. Banksia oligantha — Wagin Banksia , Species Profile and Threats Database , Department of the Environment and Heritage, Australia.
  16. George, Alex S. (1987). The Banksia Book (Second Edition). Kenthurst, New South Wales: Kangaroo Press (in association with the Society for Growing Australian Plants). ISBN   0-86417-006-8.