Banksia subg. Isostylis
Encyclopedia
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.
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.
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.
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.
in his 1810 Prodromus Florae Novae Hollandiae et Insulae Van Diemen
; thus its full name, with author citation, is Banksia subg. Isostylis R.Br. Brown's arrangement
was the first infrageneric arrangement of Banksia, making B. subg.Isostylis Banksia's first infrageneric taxon. 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, but B. ilicifolia is treated as the type because it was the only member when the subgenus was published.
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.
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.
-
When Carl Meissner
published his arrangement of Banksia
in 1856, he demoted both of Brown's subgenera to section
al 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.
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:
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 to 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.
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 cotyledon
s. 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.
Relationships within B. subg. Isostylis still remain unclear. Though Mast's studies found B. cuneata to be the most basal of the three species, 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.
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
.
s, 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. 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
.
Subgenus
In biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...
of Banksia
Banksia
Banksia is a genus of around 170 species in the plant family Proteaceae. These Australian wildflowers and popular garden plants are easily recognised by their characteristic flower spikes and fruiting "cones" and heads. When it comes to size, banksias range from prostrate woody shrubs to trees up...
. It contains three closely related species, all of which occur only in Southwest
Southwest Australia
Southwest Australia is a biodiversity hotspot that includes the Mediterranean forests, woodlands, and scrub ecoregions of Western Australia. The region has a wet-winter, dry-summer Mediterranean climate, one of five such regions in the world...
Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
. 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.
There are three species of Banksia subg. Isostylis, B. ilicifolia
Banksia ilicifolia
Banksia ilicifolia, commonly known as Holly-leaved Banksia, is a tree in the plant Proteaceae family. 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...
(Holly-leaved Banksia), B. cuneata
Banksia cuneata
Banksia cuneata, commonly known as Matchstick Banksia or Quairading Banksia, is an endangered species of flowering plants in the Proteaceae family. Endemic to southwest Western Australia, it belongs to Banksia subg...
(Matchstick Banksia) and B. oligantha
Banksia oligantha
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...
(Wagin Banksia). B. ilicifolia is widely distributed and relatively common, but the other two species are rare and threatened.
Description
B. 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 folliclesFollicle (fruit)
In botany, a follicle is a dry unilocular many-seeded fruit formed from one carpel and dehiscing by the ventral suture in order to release seeds, such as in larkspur, magnolia, banksia, peony and milkweed....
with a woolly
Tomentose
Tomentose is a term used to describe plant hairs that are flattened and matted, forming a woolly coating known as tomentum. Often the hairs are silver or gray-colored...
coating, whereas Dryandra follicles are thin and hairless; and the involucral, common and floral bracts of Isostylis are unlike those of Dryandra.
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.
Taxonomic history
B. subg. Isostylis was first published by Robert BrownRobert Brown (botanist)
Robert Brown was a Scottish botanist and palaeobotanist who made important contributions to botany largely through his pioneering use of the microscope...
in his 1810 Prodromus Florae Novae Hollandiae et Insulae Van Diemen
Prodromus Florae Novae Hollandiae et Insulae Van Diemen
Prodromus Florae Novae Hollandiae et Insulae Van Diemen is an 1810 flora of Australia by botanist Robert Brown. Often referred to as Prodromus Flora Novae Hollandiae, or by its standard botanical abbreviation Prodr. Fl. Nov. Holland., it was the first attempt at a survey of the Australian flora...
; thus its full name, with author citation, is Banksia subg. Isostylis R.Br. Brown's arrangement
Brown's taxonomic arrangement of Banksia
Robert Brown's taxonomic arrangement of Banksia was published in his 1810 Prodromus Florae Novae Hollandiae et Insulae Van Diemen, and expanded in this 1830 supplement to that publication, Supplementum Primum Prodromi Florae Novae Hollandiae...
was the first infrageneric arrangement of Banksia, making B. subg.Isostylis Banksia's first infrageneric taxon. 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
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
for the subgenus, but B. ilicifolia is treated as the type because it was the only member when the subgenus was published.
Twenty years later, Brown issued a supplement to his Prodromus entitled Supplementum Primum Prodromi Florae Novae Hollandiae
Supplementum Primum Prodromi Florae Novae Hollandiae
Supplementum primum Prodromi florae Novae Hollandiae is an 1830 supplement to Robert Brown's Prodromus florae Novae Hollandiae et Insulae Van Diemen. It may be referred to by its standard botanical abbreviation Suppl. Prodr. Fl. Nov...
; another nine Banksia species were published, but there was no change to the 1810 arrangement, and no new Isostylis species.
In 1846, Édouard Spach
Édouard Spach
Édouard Spach was a French botanist.The son of a merchant in Strasbourg, he went to Paris in 1824 where he studied botany with René Desfontaines and Antoine Laurent de Jussieu . He became the secretary of Charles-François Brisseau de Mirbel...
promoted B. subg. Isostylis to genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
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.
-
When Carl Meissner
Carl Meissner
Carl Daniel Friedrich Meissner was a Swiss botanist.Born in Bern, Switzerland on 1 November 1800, he was christened Meisner but later changed the spelling of his name to Meissner. For most of his 40 year career he was Professor of Botany at University of Basel...
published his arrangement of Banksia
Meissner's taxonomic arrangement of Banksia
Carl Meissner's taxonomic arrangement of Banksia was published in 1856, as part of his chapter on the Proteaceae in A. P. de Candolle's Prodromus systematis naturalis regni vegetabilis. It was the first attempt to provide an infrageneric classification for the genus, aside from Robert Brown's...
in 1856, he demoted both of Brown's subgenera to section
Section (botany)
In botany, a section is a taxonomic rank below the genus, but above the species. The subgenus, if present, is higher than the section, and the rank of series, if present, is below the section. Sections are typically used to help organise very large genera, which may have hundreds of species...
al 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
George Bentham
George Bentham CMG FRS was an English botanist, characterized by Duane Isely as "the premier systematic botanist of the nineteenth century".- Formative years :...
in his 1870 arrangement
Bentham's taxonomic arrangement of Banksia
George Bentham's taxonomic arrangement of Banksia was published in 1870, in Volume 5 of Bentham's Flora Australiensis. A substantial improvement on the previous arrangement, it would stand for over a century. It was eventually replaced by Alex George's 1981 arrangement, published in his classic...
for Flora Australiensis
Flora Australiensis
Flora Australiensis: a description of the plants of the Australian Territory, more commonly referred to as Flora Australiensis, and also known by its standard abbreviation Fl. Austral., is a seven-volume flora of Australia published between 1863 and 1878 by George Bentham, with the assistance of...
, but Bentham also published a putative variety of B. ilicifolia, B. i. var. integrifolia, based on specimens collected by Ludwig Preiss
Ludwig Preiss
Johann August Ludwig Preiss was a German-born British botanist and zoologist.Preiss was born in Herzberg am Harz, Germany. He obtained a doctorate, probably at Hamburg, then emigrated to Western Australia...
near the Swan River in Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
. This was later overturned.
In 1905, James Britten
James Britten
James Britten was an English botanist.-Biography:Born in Chelsea, London, he moved to High Wycombe in 1865 to begin a medical career. However he became increasingly interested in botany, and began writing papers on the subject...
challenged the genus name Banksia, on the grounds that Banksia J.R.Forst
Johann Reinhold Forster
Johann Reinhold Forster was a German Lutheran pastor and naturalist of partial Scottish descent who made contributions to the early ornithology of Europe and North America...
& G.Forst
Georg Forster
Johann Georg Adam Forster was a German naturalist, ethnologist, travel writer, journalist, and revolutionary. At an early age, he accompanied his father on several scientific expeditions, including James Cook's second voyage to the Pacific...
had precedent over Banksia L.f.
Carolus Linnaeus the Younger
Carl Linnaeus the Younger, Carl von Linné or Carolus Linnaeus the Younger was a Swedish naturalist...
. Britten adopted the name Isostylis for the entire genus, republishing the names Isostylis dentata (L.f.) Britten for B. dentata
Banksia dentata
The Tropical Banksia is a species of small tree in the plant genus Banksia.-Distribution and habitat:It occurs throughout northern Australia, and also extends into New Guinea and the Aru Islands...
(Tropical Banksia), Isostylis ericifolia (L.f.) Britten for B. ericifolia
Banksia ericifolia
Banksia ericifolia, the Heath-leaved Banksia , is a species of woody shrub of the Proteaceae family native to Australia. It grows in two separate regions of Central and Northern New South Wales east of the Great Dividing Range...
(Heath-leaved Banksia), Isostylis integrifolia (L.f.) Britten for B. integrifolia
Banksia integrifolia
Banksia integrifolia, commonly known as Coast Banksia, is a species of tree that grows along the east coast of Australia. One of the most widely distributed Banksia species, it occurs between Victoria and Central Queensland in a broad range of habitats, from coastal dunes to mountains...
(Coast Banksia) and Isostylis serrata (L.f.) Britten for B. serrata
Banksia serrata
Banksia serrata, commonly known as Old Man Banksia, Saw Banksia, Saw-tooth Banksia and Red Honeysuckle, is a species of woody shrub or tree of the genus Banksia in the Proteaceae family. Native the east coast of Australia, it is found from Queensland through to Victoria with outlying populations on...
(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
Alex George
Alexander Segger George is a Western Australian botanist. He is the authority on the plant genera Banksia and Dryandra...
promoted it back to subgenus rank, and published a second species, B. cuneata
Banksia cuneata
Banksia cuneata, commonly known as Matchstick Banksia or Quairading Banksia, is an endangered species of flowering plants in the Proteaceae family. Endemic to southwest Western Australia, it belongs to Banksia subg...
. In discussing the subgenus, George commented that there had been calls to transfer Isostylis into Dryandra
Dryandra
Banksia ser. Dryandra is a series of 94 species of shrub to small tree in the plant genus Banksia. It was considered a separate genus named Dryandra until early 2007, when it was merged into Banksia on the basis of extensive molecular and morphological evidence that Banksia was paraphyletic with...
, 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
Banksia oligantha
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...
, was published by George in 1988.
In 1996, Kevin Thiele
Kevin Thiele
Kevin R. Thiele is curator of the Western Australian Herbarium. His research interests include the systematics of the plant families Proteaceae, Rhamnaceae and Violaceae, and the conservation ecology of grassy woodland ecosystems...
and Pauline Ladiges published a revised arrangement
Thiele and Ladiges' taxonomic arrangement of Banksia
Kevin Thiele and Pauline Ladiges' taxonomic arrangement of Banksia, published in 1996, was a novel taxonomic arrangement that was intended to align the taxonomy of Banksia more closely with the phylogeny that they had inferred from their cladistic analysis of the genus...
based on a cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
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.
Thiele and Ladiges' arrangement was not accepted by George, and was largely discarded by him in his 1999 arrangement
George's taxonomic arrangement of Banksia
Alex George's taxonomic arrangement of Banksia was the first modern-day arrangement for that genus. First published in 1981 in the classic monograph The genus Banksia L.f. , it superseded the arrangement of George Bentham, which had stood for over a hundred years. It was overturned in 1996 by Kevin...
. The placement and circumscription of B. subg. Isostylis was unaffected and can be summarised as follows:
- BanksiaBanksiaBanksia is a genus of around 170 species in the plant family Proteaceae. These Australian wildflowers and popular garden plants are easily recognised by their characteristic flower spikes and fruiting "cones" and heads. When it comes to size, banksias range from prostrate woody shrubs to trees up...
- B. subg. BanksiaBanksia subg. BanksiaBanksia 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.-Banksia verae:B. subg...
(3 sections, 11 series, 73 species, 11 subspecies, 14 varieties) - B. subg. Isostylis
- B. ilicifoliaBanksia ilicifoliaBanksia ilicifolia, commonly known as Holly-leaved Banksia, is a tree in the plant Proteaceae family. 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...
- B. oliganthaBanksia oliganthaBanksia 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...
- B. cuneataBanksia cuneataBanksia cuneata, commonly known as Matchstick Banksia or Quairading Banksia, is an endangered species of flowering plants in the Proteaceae family. Endemic to southwest Western Australia, it belongs to Banksia subg...
- B. ilicifolia
- B. subg. Banksia
Since 1998, Austin Mast
Austin Mast
Austin R. Mast is a research botanist. Born in 1972, he obtained a Ph.D. from the University of Wisconsin–Madison in 2000. He is currently an associate professor within the Department of Biological Science at Florida State University , and has been director of FSU's since August 2003.One of his...
has been publishing results of ongoing cladistic analyses of DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
data for the subtribe Banksiinae. His analyses has provided compelling evidence for the paraphyly
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
of Banksia with respect to Dryandra, and suggest an overall phylogeny that is very greatly different to 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
Banksia elegans
The Elegant Banksia is a species of shrub or small tree in the plant genus Banksia. It occurs only over a 65 square kilometre area north and west of Eneabba, Western Australia.-Ecology:...
(Elegant Banksia) and B. attenuata
Banksia attenuata
Banksia attenuata, commonly known as the candlestick banksia or slender banksia, is a species of plant in the proteaceae family. Commonly a tree, it reaches 10 m high, but is often a shrub in dryer areas 0.4 to 2 m high...
(Candlestick Banksia). It falls a substantial distance from Dryandra, suggesting that similarities between those two groups are indeed superficial.
Early in 2007, Mast and Thiele initiated a rearrangement of Banksia by merging Dryandra
Dryandra
Banksia ser. Dryandra is a series of 94 species of shrub to small tree in the plant genus Banksia. It was considered a separate genus named Dryandra until early 2007, when it was merged into Banksia on the basis of extensive molecular and morphological evidence that Banksia was paraphyletic with...
into it, and publishing B. subg. Spathulatae
Banksia subg. Spathulatae
Banksia subg. Spathulatae is a valid botanic name for a subgenus of Banksia. It was published in 2007 by Austin Mast and Kevin Thiele, and defined as containing all those Banksia species having spathulate cotyledons...
for the species having spoon-shaped cotyledon
Cotyledon
A cotyledon , is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon may become the embryonic first leaves of a seedling. The number of cotyledons present is one characteristic used by botanists to classify the flowering plants...
s. 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.
Relationships within B. subg. Isostylis still remain unclear. Though Mast's studies found B. cuneata to be the most basal of the three species, a 2004 study of genetic divergence
Genetic divergence
Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes through time, often after the populations have become reproductively isolated for some period of time...
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
High Rainfall Zone
The High Rainfall Zone is one of three biogeographic zones into which south west Western Australia is divided, the others being the Transitional Rainfall Zone and the Low Rainfall Zone....
where relictual species are most common, whereas the others are restricted to the Transitional Rainfall Zone
Transitional Rainfall Zone
The Transitional Rainfall Zone is one of three biogeographic zones into which south west Western Australia is divided, the others being the High Rainfall Zone and the Low Rainfall Zone...
, where more recently evolved species are most common.
Distribution
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
's South West Botanical Province. B. ilicifolia is widespread within 70 kilometres of the coast from Mount Lesueur
Mount Lesueur
Mount Lesueur is a near-circular, flat-topped mesa located 21 kilometres from Jurien Bay in Western Australia. It rises above the surrounding lateritic plain of Lesueur National Park which has eroded away around it....
in the north, south to Cape Leeuwin
Cape Leeuwin
Cape Leeuwin is the most south-westerly mainland point of the Australian Continent, in the state of Western Australia.A few small islands and rocks, the St Alouarn Islands, extend further to the south. The nearest settlement, north of the cape, is Augusta. South-east of Cape Leeuwin, the coast...
and east to Albany
Albany, Western Australia
Albany is a port city in the Great Southern region of Western Australia, some 418 km SE of Perth, the state capital. As of 2009, Albany's population was estimated at 33,600, making it the 6th-largest city in the state....
. The other two species occur further inland, and have quite limited distributions. B. cuneata occurs Brookton
Brookton, Western Australia
Brookton is a town located in the Wheatbelt region of Western Australia, Australia, from the state capital, Perth via the Brookton Highway where it crosses the Great Southern Highway. The town is also located on the Great Southern railway line. It is located within, and is the seat of government...
and Bruce Rock
Bruce Rock, Western Australia
Bruce Rock is a town located in the Eastern Wheatbelt region of Western Australia, approximately east of Perth and southwest of Merredin. It is the main town in the Shire of Bruce Rock....
in the Avon Wheatbelt
Avon Wheatbelt
Avon Wheatbelt is an Interim Biogeographic Regionalisation for Australia region in Western Australia and part of the larger Southwest Australia savanna ecoregion.-Further reading:...
biogeographic
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
region; while B. oligantha occurs slightly further south, in the vicinity of Wagin
Wagin, Western Australia
Wagin is a town and shire in the Great Southern region of Western Australia, approximately 225 km south-east of Perth on the Great Southern Highway between Narrogin and Katanning. It is also on State Route 107. The main industries are wheat and sheep farming.-History:The name of the town is...
.
Ecology
Ecologically, B. subg. Isostylis is similar to other Banksias. As with other Banksia taxa, all three species have proteoid rootProteoid root
Proteoid roots, also known as cluster roots, are plant roots that form clusters of closely spaced short lateral rootlets. They may form a two to five centimetre thick mat just beneath the leaf litter. They enhance nutrient uptake, possibly by chemically modifying the soil environment to improve...
s, 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
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
-deficient native soils of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. They lack a lignotuber
Lignotuber
A lignotuber is a starchy swelling of the root crown possessed by some plants as a protection against destruction of the plant stem by fire. The crown contains buds from which new stems may sprout, and a sufficient store of nutrients to support a period of growth in the absence of...
, so shrubs are killed by bushfire; mature trees of B. ilicifolia have a limited ability to resprout from epicormic buds on the trunk. But like all Banksias they release their aerial seed bank following a bushfire. This adaptation, known as serotiny
Serotiny
Serotiny is an ecological adaptation exhibited by some seed plants, in which seed release occurs in response to an environmental trigger, rather than spontaneously at seed maturation. The most common and best studied trigger is fire, and the term serotiny is often used to refer to this specific case...
, ensures the rapid regeneration of populations killed by fire.
B. cuneata and B. oligantha have been declared rare under both Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
's Wildlife Conservation Act 1950
Wildlife Conservation Act 1950
The Wildlife Conservation Act 1950 is an act of the Western Australian Parliament that provides the statute relating to conservation and legal protection of flora and fauna....
, and the federal Environment Protection and Biodiversity Conservation Act 1999
Environment Protection and Biodiversity Conservation Act 1999
The Environment Protection and Biodiversity Conservation Act 1999 is an Act of the Parliament of Australia that provides a framework for protection of the Australian environment, including its biodiversity and its natural and culturally significant places...
. Threats include loss of habitat, Phytophthora cinnamomi
Phytophthora cinnamomi
Phytophthora cinnamomi is a soil-borne water mould that produces an infection which causes a condition in plants called root rot or dieback. The plant pathogen is one of the world's most invasive species and is present in over 70 countries from around the world.- Life cycle and effects on plants :P...
dieback, and grazing on seedlings by feral rabbits
Rabbits in Australia
In Australia, rabbits are a serious mammalian pest and are an invasive species. Annually, European rabbits cause millions of dollars of damage to crops.-Effects on Australia's ecology:...
.