Banksia oligantha
Encyclopedia
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 inflorescence
s, 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 (October to December).
First collected in 1984 near the wheatbelt town of Wagin
, Banksia oligantha was officially described in 1987 by Australian botanist Alex George
. Several scattered populations survive in fragments of remnant bushland in a region which has been mostly cleared for agriculture. It has been listed as Declared Rare Flora by the Western Australian Government.
with few main stems. Reports of its maximum height vary from 3 m (10 ft) to 5 m (16 ft). When not in flower it is said to look somewhat like Banksia sessilis (Parrot Bush). It has smooth grey bark for the most part, though bark near the base of the trunk may be lightly fissured in older trees. Young stems are covered in hairs, both short and soft, and long and coarse; these are lost with age.
Leaves are deep green and glossy above, and a pale matte green below. They are roughly oval-shaped, but concave rather than laying flat. There is a sharp point at the tip, and two to four more such points along each margin. They range in length from 1.5 to 3.7 cm (0.6–1.5 in), and in width from 0.4 to 2.0 cm (0.16–0.79 in), with a petiole
2 to 3 mm (0.08–0.12 in) long. Young leaves have a coating of woolly hairs on both sides, but these are soon lost except in pits in the undersurface.
Appearing from October to December (late spring), the flowers occur in dome-shaped heads
from 2.5 to 3 cm (1–1.2 in) in diameter, growing at the ends of branches. These comprise just 20 to 35 individual flowers, enclosed at the base by a whorl of furry involucral bracts 2 to 4 mm (0.08–0.16 in) long. As with most other Proteaceae
, each flower consists of a perianth
comprising four united tepal
s, and a single pistil
, the style of which is initially enclosed within the limb of the perianth, but breaks free at anthesis
. In B. oligantha, the perianth is 21 to 22 mm (0.8–0.9 in) long, with a limb of 3 to 3.5 mm (0.12–0.14 in). Perianth colour grades from red at the base to pale yellow at the limb. The styles are straight, 19 to 24 mm (0.75–0.94 in) long, and uniformly cream.
Old flowers soon fall from the flower heads, revealing a woody dome with 1 to 6 follicle
s embedded in it. These are a mottled grey colour, smooth, and shortly furry. They are oval-shaped, measuring 14 to 19 mm (0.55–0.75 in) long by 10 to 15 mm (0.4–0.6 in) high by 8 to 9 mm (0.3–0.35 in) wide. Each follicle contains up to two winged seeds, from 17 to 20 mm (0.7–0.9 in) long.
Banksia oligantha is most easily distinguished from the other two species in B. subg. Isostylis by its smaller leaves, flowers and fruit. Its foliage is also not as prickly as that of B. cuneata
.
's Department of Conservation and Land Management (now the Department of Environment and Conservation) in September 1984, during a survey of Wangeling Gully Nature Reserve (Nature Reserve 9098), about 28 km (17 mi) northwest of Wagin. Two months later, on 18 November 1984, Anne Taylor collected from the same location what would become the type specimen. It was recognised as a new species well before a name was published for it, and was referred to in the interim by the informal names "Banksia aff. Cuneata" and "Banksia sp. Wagin". Alex George
included an entry for it under the name Banksia oligantha in the 1987 second edition of his The Banksia Book, but the formal publication of that name did not occur until the following year, when George's "New taxa and notes on Banksia L.f. (Proteaceae)" appeared. The specific epithet oligantha derives from the Greek
oligo- ("few") and anthos ("flower"), in reference to the low number of flowers per flower head.
The species has an uneventful nomenclatural history: it has no synonyms
, and no subspecies or varieties have been published.
because of its dome-shaped flower heads. A 1996 cladistic
analysis of the genus
by botanists Kevin Thiele
and Pauline Ladiges based on morphology yielded no information about the circumscription of B. subg. Isostylis or the relationships within it, so George's placement of this species was retained. George largely discarded Thiele and Ladiges' changes in his 1999 arrangement
, but again B. oliganthas placement was unaffected, and the placement of B. oligantha there can be summarised as follows:
Since 1998, American botanist Austin Mast
and co-authors have been publishing results of ongoing cladistic analyses of DNA sequence
data for the subtribe Banksiinae, which then comprised genera Banksia and Dryandra
. Their analyses suggest a phylogeny that differs greatly from George's taxonomic arrangement. B. oligantha resolves as sister taxon (that is, next closest relative) to B. ilicifolia, and B. cuneata resolves as sister to these two. This suggests a monophyletic B. subg. Isostylis; yet the clade appears fairly derived
(that it, it evolved relatively recently), implying that B. subgenus Isostylis may not merit subgeneric rank.
Early in 2007, Mast and Thiele rearranged the genus Banksia by merging Dryandra into it, and publishing B. subg. Spathulatae
for the taxa having spoon-shaped cotyledon
s; thus B. subg. Banksia was redefined as encompassing taxa lacking spoon-shaped cotyledons. They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, if Mast and Thiele's nomenclatural changes are taken as an interim arrangement, then B. oligantha is placed in B. subg. Banksia.
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 southernmost (and closest) population of B. cuneata, which has 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 relict
ual species are most common, whereas the others are restricted to the Transitional Rainfall Zone
, where more recently evolved species are most common.
region of the Southwest Botanical Province of Western Australia
. Four populations are known, containing about 1,700 adult plants in total:
The species grows in sand dunes of white, white-grey or yellow-brown sand, amongst a system of ephemeral salt creeks. Populations occur both in low-lying areas near creeks, and atop dunes. The vegetation has been described as low open woodland over heath, and as tall open shrubland with some scattered trees.
is probably around 10 to 30 years.
Six species of honeyeater
have been observed feeding at its flowers, as have insects including honeybees, ants, butterflies, beetles and native bees. Both birds and insects function as pollinators, but honeybees are probably not very effective: in one study only about 4% of honeybees collected pollen, and they tended to move from inflorescence to inflorescence on the same plant, rather than moving between plants.
Assessments of the mating system
of this species have found that outcrossing
rates vary between populations, with populations in disturbed environments tending to be more inbred
than populations in relatively intact bushland. This has been attributed to a range of causes. Firstly, the higher density of disturbed populations leads to greater rates of mating between neighbouring plants, resulting in more genetic structure
and thus more effective selfing
. Secondly, disturbed populations usually lack an understorey, and so cannot support a resident population of honeyeaters; instead, they rely upon sporadic visits for pollination. The greatly reduced pollination rates means fewer outcrossing fertilisations on average, leading to less selection
against inbred fertilisations.
Like many plants in south-west Western Australia, B. oligantha is adapted to an environment in which bushfire events are relatively frequent. Most Banksia species can be placed in one of two broad groups according to their response to fire: reseeders are killed by fire, but fire also triggers the release of their canopy seed bank
, thus promoting recruitment of the next generation; resprouter
s survive fire, resprouting from a lignotuber
or, more rarely, epicormic buds
protected by thick bark. B. oligantha is a reseeder; it has thin bark, and lacks a lignotuber
, so it is killed by fire. However the species is weakly serotinous: fire triggers seed release, yet seed release still occurs in the absence of fire.
Seed germination rates are quite high. One study found germination rates better than 77% in most batches tested. Seed is likely to remain viable for a long time, as seed of the closely related B. cuneata remains viable for around ten years.
(EPBC Act), and as rare under Western Australia's Wildlife Conservation Act 1950
. These rankings are due to its small and severely fragmented distribution, and the ongoing degradation of its habitat. Threats include grazing by sheep
and rabbit
s, drought
, the drift of aerosol
chemicals from surrounding farmland, invasion by weed
s, and rising salinity
. Studies have shown it to be moderately susceptible to Phytophthora cinnamomi
dieback.
s.
Propagation is by seed, but these are hard to obtain. Seeds do not require any treatment before sowing, and take 37 to 40 days to germinate
. Propagation by cutting
has not been attempted, but might be possible, since the closely related B. cuneata has been propagated this way, albeit with unpredictable results. The plant should be grown in deep, acidic to neutral sand at a sheltered site. It is recommended to prune it when young, to encourage branching.
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
in the plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Proteaceae
Proteaceae
Proteaceae is a family of flowering plants distributed in the Southern Hemisphere. The family comprises about 80 genera with about 1600 species. Together with the Platanaceae and Nelumbonaceae they make up the order Proteales. Well known genera include Protea, Banksia, Embothrium, Grevillea,...
endemic to south west
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...
. It belongs to Banksia subg. Isostylis
Banksia subg. Isostylis
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...
, a subgenus of three closely related 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...
species with dome-shaped heads as inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
s, 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
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
which appear in late Spring (October to December).
First collected in 1984 near the wheatbelt town 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...
, Banksia oligantha was officially described in 1987 by Australian botanist Alex George
Alex George
Alexander Segger George is a Western Australian botanist. He is the authority on the plant genera Banksia and Dryandra...
. Several scattered populations survive in fragments of remnant bushland in a region which has been mostly cleared for agriculture. It has been listed as Declared Rare Flora by the Western Australian Government.
Description
Banksia oligantha grows as a single-trunked small tree or as an erect shrubShrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
with few main stems. Reports of its maximum height vary from 3 m (10 ft) to 5 m (16 ft). When not in flower it is said to look somewhat like Banksia sessilis (Parrot Bush). It has smooth grey bark for the most part, though bark near the base of the trunk may be lightly fissured in older trees. Young stems are covered in hairs, both short and soft, and long and coarse; these are lost with age.
Leaves are deep green and glossy above, and a pale matte green below. They are roughly oval-shaped, but concave rather than laying flat. There is a sharp point at the tip, and two to four more such points along each margin. They range in length from 1.5 to 3.7 cm (0.6–1.5 in), and in width from 0.4 to 2.0 cm (0.16–0.79 in), with a petiole
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
2 to 3 mm (0.08–0.12 in) long. Young leaves have a coating of woolly hairs on both sides, but these are soon lost except in pits in the undersurface.
Appearing from October to December (late spring), the flowers occur in dome-shaped heads
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
from 2.5 to 3 cm (1–1.2 in) in diameter, growing at the ends of branches. These comprise just 20 to 35 individual flowers, enclosed at the base by a whorl of furry involucral bracts 2 to 4 mm (0.08–0.16 in) long. As with most other Proteaceae
Proteaceae
Proteaceae is a family of flowering plants distributed in the Southern Hemisphere. The family comprises about 80 genera with about 1600 species. Together with the Platanaceae and Nelumbonaceae they make up the order Proteales. Well known genera include Protea, Banksia, Embothrium, Grevillea,...
, each flower consists of a perianth
Petal
Petals are modified leaves that surround the reproductive parts of flowers. They often are brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are usually accompanied by another set of special leaves called sepals lying...
comprising four united tepal
Tepal
Tepals are elements of the perianth, or outer part of a flower, which include the petals or sepals. The term tepal is more often applied specifically when all segments of the perianth are of similar shape and color, or undifferentiated, which is called perigone...
s, and a single pistil
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
, the style of which is initially enclosed within the limb of the perianth, but breaks free at anthesis
Anthesis
Anthesis is the period during which a flower is fully open and functional. It may also refer to the onset of that period.The onset of anthesis is spectacular in some species. In Banksia species, for example, anthesis involves the extension of the style far beyond the upper perianth parts...
. In B. oligantha, the perianth is 21 to 22 mm (0.8–0.9 in) long, with a limb of 3 to 3.5 mm (0.12–0.14 in). Perianth colour grades from red at the base to pale yellow at the limb. The styles are straight, 19 to 24 mm (0.75–0.94 in) long, and uniformly cream.
Old flowers soon fall from the flower heads, revealing a woody dome with 1 to 6 follicle
Follicle (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....
s embedded in it. These are a mottled grey colour, smooth, and shortly furry. They are oval-shaped, measuring 14 to 19 mm (0.55–0.75 in) long by 10 to 15 mm (0.4–0.6 in) high by 8 to 9 mm (0.3–0.35 in) wide. Each follicle contains up to two winged seeds, from 17 to 20 mm (0.7–0.9 in) long.
Banksia oligantha is most easily distinguished from the other two species in B. subg. Isostylis by its smaller leaves, flowers and fruit. Its foliage is also not as prickly as that of 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...
.
Discovery and naming
Banksia oligantha was discovered by Ken Wallace of the Government of Western AustraliaGovernment of Western Australia
The formation of the Government of Western Australia is prescribed in its Constitution, which dates from 1890, although it has been amended many times since then...
's Department of Conservation and Land Management (now the Department of Environment and Conservation) in September 1984, during a survey of Wangeling Gully Nature Reserve (Nature Reserve 9098), about 28 km (17 mi) northwest of Wagin. Two months later, on 18 November 1984, Anne Taylor collected from the same location what would become the type specimen. It was recognised as a new species well before a name was published for it, and was referred to in the interim by the informal names "Banksia aff. Cuneata" and "Banksia sp. Wagin". Alex George
Alex George
Alexander Segger George is a Western Australian botanist. He is the authority on the plant genera Banksia and Dryandra...
included an entry for it under the name Banksia oligantha in the 1987 second edition of his The Banksia Book, but the formal publication of that name did not occur until the following year, when George's "New taxa and notes on Banksia L.f. (Proteaceae)" appeared. The specific epithet oligantha derives from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
oligo- ("few") and anthos ("flower"), in reference to the low number of flowers per flower head.
The species has an uneventful nomenclatural history: it has no synonyms
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
, and no subspecies or varieties have been published.
Infrageneric placement
George placed B. oligantha in subgenus IsostylisBanksia subg. Isostylis
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...
because of its dome-shaped flower heads. A 1996 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 the genus
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...
by botanists 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 based on morphology yielded no information about the circumscription of B. subg. Isostylis or the relationships within it, so George's placement of this species was retained. George largely discarded Thiele and Ladiges' changes 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...
, but again B. oliganthas placement was unaffected, and the placement of B. oligantha there 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. IsostylisBanksia subg. IsostylisBanksia 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...
- 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. oligantha
- 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, American botanist 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...
and co-authors have 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, which then comprised genera Banksia and 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...
. Their analyses suggest a phylogeny that differs greatly from George's taxonomic arrangement. B. oligantha resolves as sister taxon (that is, next closest relative) to B. ilicifolia, and B. cuneata resolves as sister to these two. This suggests a monophyletic B. subg. Isostylis; yet the clade appears fairly derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
(that it, it evolved relatively recently), implying that B. subgenus Isostylis may not merit subgeneric rank.
Early in 2007, Mast and Thiele rearranged the genus Banksia by merging Dryandra 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 taxa 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; thus B. subg. Banksia was redefined as encompassing taxa lacking spoon-shaped cotyledons. They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, if Mast and Thiele's nomenclatural changes are taken as an interim arrangement, then B. oligantha is placed in B. subg. Banksia.
Phylogeny
Relationships between B. oligantha and the other members of 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 divergenceGenetic 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 southernmost (and closest) population of B. cuneata, which has 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 relict
Relict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....
ual 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 and habitat
Banksia oligantha occurs over a range of about 100 kilometres (60 mi) in southern parts of the Avon WheatbeltAvon 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:...
region of the Southwest Botanical Province of 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...
. Four populations are known, containing about 1,700 adult plants in total:
- The first known population, at Wangelling Gully Nature Reserve in Tarwonga. This population appears to be in decline: in 1988 it was estimated as containing from 500 to 800 plants, but a 2001 survey found only 198 adults, 1 seedling, and 286 dead plants; and a 2004 survey found 135 adults, no seedlings, and 174 dead plants.
- A healthy population at Katanning, spanning two Native Settlement reserves and some private property. This population appears to be increasing; a 2004 survey found nearly 1400 adult plants and over 500 seedlings.
- A small population at Dudinin, spanning a nature reserve and private property. This population is apparently in decline. No seedlings have ever been reported at this location, and from 1997 to 2004 the number of reported adults feel from around 110 to 13.
- A recently discovered healthy population on private property at Toolibin. A 2004 survey counted 188 adults, 35 seedlings, and 36 dead plants.
The species grows in sand dunes of white, white-grey or yellow-brown sand, amongst a system of ephemeral salt creeks. Populations occur both in low-lying areas near creeks, and atop dunes. The vegetation has been described as low open woodland over heath, and as tall open shrubland with some scattered trees.
Ecology
Little has been published on the ecology of B. oligantha. Its lifespanMaximum life span
Maximum life span is a measure of the maximum amount of time one or more members of a population has been observed to survive between birth and death.Most living species have at least one upper limit on the number of times cells can divide...
is probably around 10 to 30 years.
Six species of honeyeater
Honeyeater
The honeyeaters are a large and diverse family of small to medium sized birds most common in Australia and New Guinea, but also found in New Zealand, the Pacific islands as far east as Samoa and Tonga, and the islands to the north and west of New Guinea known as Wallacea...
have been observed feeding at its flowers, as have insects including honeybees, ants, butterflies, beetles and native bees. Both birds and insects function as pollinators, but honeybees are probably not very effective: in one study only about 4% of honeybees collected pollen, and they tended to move from inflorescence to inflorescence on the same plant, rather than moving between plants.
Assessments of the mating system
Mating system
A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to higher animals, it specifies which males mate with which females, under which circumstances; recognised animal mating systems include monogamy,...
of this species have found that outcrossing
Outcrossing
Outcrossing is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities...
rates vary between populations, with populations in disturbed environments tending to be more inbred
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
than populations in relatively intact bushland. This has been attributed to a range of causes. Firstly, the higher density of disturbed populations leads to greater rates of mating between neighbouring plants, resulting in more genetic structure
Genetic structure
Genetic structure refers to any pattern in the genetic makeup of individuals within a population.In the absence of genetic structure, one can infer little to nothing about the genetic makeup of an individual by studying other members of the population...
and thus more effective selfing
Effective selfing model
The effective selfing model is a mathematical model that describes the mating system of a plant population in terms of the degree of self-fertilisation present....
. Secondly, disturbed populations usually lack an understorey, and so cannot support a resident population of honeyeaters; instead, they rely upon sporadic visits for pollination. The greatly reduced pollination rates means fewer outcrossing fertilisations on average, leading to less selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
against inbred fertilisations.
Like many plants in south-west Western Australia, B. oligantha is adapted to an environment in which bushfire events are relatively frequent. Most Banksia species can be placed in one of two broad groups according to their response to fire: reseeders are killed by fire, but fire also triggers the release of their canopy seed bank
Canopy seed bank
A canopy seed bank or aerial seed bank is the aggregate of viable seed stored by a plant in its canopy. Canopy seed banks occur in plants that postpone seed release for some reason....
, thus promoting recruitment of the next generation; resprouter
Resprouter
Resprouters are plant species that are able to survive fire by the activation of dormant vegetative buds to produce regrowth.Plants may resprout by means of lignotubers at the base or epicormic buds on the trunk or major branches....
s survive fire, resprouting from 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...
or, more rarely, epicormic buds
Epicormic shoot
An epicormic shoot is a shoot growing from an epicormic bud which lies underneath the bark of a trunk, stem, or branch of a plant.-Epicormic buds:...
protected by thick bark. B. oligantha is a reseeder; it has thin bark, and lacks 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 it is killed by fire. However the species is weakly serotinous: fire triggers seed release, yet seed release still occurs in the absence of fire.
Seed germination rates are quite high. One study found germination rates better than 77% in most batches tested. Seed is likely to remain viable for a long time, as seed of the closely related B. cuneata remains viable for around ten years.
Conservation
Banksia oligantha is listed as an endangered species under the federal Environment Protection and Biodiversity Conservation Act 1999Environment 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...
(EPBC Act), and as rare under Western Australia'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....
. These rankings are due to its small and severely fragmented distribution, and the ongoing degradation of its habitat. Threats include grazing by sheep
Domestic sheep
Sheep are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species in the genus Ovis, in everyday usage it almost always refers to Ovis aries...
and rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...
s, drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
, the drift of aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
chemicals from surrounding farmland, invasion by weed
Weed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
s, and rising salinity
Salinity in Australia
Soil salinity and dryland salinity are two problems degrading the environment of Australia. Salinity is a concern in most states, but especially in the south-west of Western Australia....
. Studies have shown it to be moderately susceptible to 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.
Cultivation
Banksia oligantha is rarely seen in cultivation, though it is said to merit more consideration than it receives. It is a fast-growing plant that flowers prolifically, producing "lovely masses of matchstick-like cream flowers". However, its prickly foliage makes it unsuitable for growth near paths, it is prone to lose branches in strong wind, and it is often attacked by woodboring beetleWoodboring beetle
The term woodboring beetle encompasses many species and families of beetles whose larval or adult forms eat and destroy wood . Larval stages of some are commonly known as woodworms.-Invasion and control:...
s.
Propagation is by seed, but these are hard to obtain. Seeds do not require any treatment before sowing, and take 37 to 40 days to germinate
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
. Propagation by cutting
Cutting
Cutting is the separation of a physical object, or a portion of a physical object, into two portions, through the application of an acutely directed force. An implement commonly used for cutting is the knife or in medical cases the scalpel...
has not been attempted, but might be possible, since the closely related B. cuneata has been propagated this way, albeit with unpredictable results. The plant should be grown in deep, acidic to neutral sand at a sheltered site. It is recommended to prune it when young, to encourage branching.