Banksia Cuneata

''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 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).

Although ''B. cuneata'' was first collected before 1880, it was not until 1981 that Australian botanist Alex George formally described and named the species. There are two genetically distinct population groups, but no recognised varieties. This ''Banksia'' is classified as endangered, surviving in fragments of remnant bushland in a region which has been 93% cleared for agriculture. As ''Banksia cuneata'' is killed by fire and regenerates from seed, it is highly sensitive to bushfire frequency—fires recurring within four years could wipe out populations of plants not yet mature enough to set seed. ''Banksia cuneata'' is rarely cultivated, and its prickly foliage limits its utility in the cut flower industry.

Description

''Banksia cuneata'' grows as a shrub or small tree up to high, without a lignotuber. It has one or more main trunks with smooth grey bark, and many branches. Young stems are covered in coarse hairs, but these are lost as the stems age. The leaves are wedge-shaped with serrated edges, having from one to five teeth along each side. They range from long and wide, on a petiole of 2 to 3 mm. The upper surface is dull green; as with the stems, both leaf surfaces are covered in coarse hairs when young, but these are soon lost.

Flowers occur in dome-shaped heads from three to four cm (1.2–1.6 in) in diameter, growing at the ends of branches. They comprise 55 to 65 individual flowers, enclosed at the base by a whorl of short involucral bracts. As with most other Proteaceae, each flower consists of a perianth comprising four united tepals, and a single pistil, the style of which is initially enclosed within the limb of the perianth, but breaks free at anthesis. In ''B. cuneata'', the perianth is about long, with a limb of about . Prior to anthesis, the long thin perianth topped by a prominent limb resembles a matchstick, which explains one common name for this species. At first, the perianth is mostly cream, being pink only near its base; it later becomes pink throughout. The style is initially cream, but turns red; the pollen presenter is green.

Old flowers soon fall from the flower heads (often called cones at this stage), revealing a woody base which may have up to five follicles embedded in it. These are a mottled grey colour, smooth, felted with short fine hairs, and measure from high, along the seam, and across the seam. Each follicle contains up to two seeds; these are roughly triangular in shape, with a large papery wing.

''Banksia cuneata'' is most easily distinguished from the other two species in ''B.'' subg. ''Isostylis'' by its brighter flowers and duller leaves. It further differs from '' B. ilicifolia'' in its smaller habit; its smooth bark; its smaller leaves, flowers and fruit; and in its sequence of flower colour changes. The leaves, flowers and fruit of '' B. oligantha'' are smaller still, and its foliage is not as prickly as that of ''B. cuneata''.

Taxonomy

Discovery and naming

The earliest known specimen collection of ''B. cuneata'' was made by Julia Wells some time before 1880. What would later become the type specimen for the species was collected by Western Australian botanist and ''Banksia'' expert Alex George on 20 November 1971, from Badjaling Nature Reserve, about east of Quairading, at . The species was finally published by George nearly a decade later, in his 1981 monograph " The genus ''Banksia'' L.f. (Proteaceae)". The specific epithet is from the Latin ''cuneatus'' ("wedge-shaped"), in reference to the shape of the leaves.

The species has an uneventful nomenclatural history: it has no synonyms, and no subspecies or varieties have been published. It bears the common names of Matchstick Banksia or Quairading Banksia.

Infrageneric placement

George placed ''B. cuneata'' in subgenus ''Isostylis'' because of its dome-shaped flower heads. A 1996 cladistic analysis of the genus by botanists Kevin Thiele and Pauline Ladiges yielded no information about the circumscription of ''B.'' subg. ''Isostylis'', nor of the relationships within it, so George's placement of this species was retained in their arrangement. That arrangement was not accepted by George, and was largely discarded by him in his 1999 arrangement. The placement of ''B. cuneata'' there was unaffected, and can be summarised as follows:
:'' 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, 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. ''Banksia cuneata'' resolves as the next closest relative, or "sister", to a clade containing ''B. ilicifolia'' and ''B. oligantha'', suggesting a monophyletic ''B.'' subg. ''Isostylis''; but the clade appears fairly derived (that it, it evolved relatively recently), suggesting that ''B.'' subg. ''Isostylis'' may not merit subgeneric rank.

Early in 2007, Mast and Thiele rearranged the genus ''Banksia'' by merging ''Dryandra'' into it, and published ''B.'' subg. ''Spathulatae'' for the taxa having spoon-shaped cotyledons; 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. cuneata'' is placed in ''B.'' subg. ''Banksia''.

Phylogeny

Relationships between ''B. cuneata'' 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 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 southernmost population of ''B. cuneata'', which has both genetic and phenetic affinities with ''B. oligantha'' located to the southeast. 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.

Distribution and habitat

An endangered species, ''B. cuneata'' occurs only over a range around Pingelly and Quairading, in Western Australia. It favours deep yellow sand at elevations between , in woodland habitat. It often grows in association with '' Banksia prionotes'' and ''Xylomelum angustifolium''.

Reports on the number of populations and individuals vary widely. A survey in 1982 reported 450 plants in five populations, with the largest population comprising 300 plants. In 1988, however, only four populations comprising 300 plants were found; surprisingly, only fifty plants could be found in the location where a population of 300 had previously been reported; yet there were no dead plants, and no evidence of disturbance. Since then the number of populations reported have ranged from 6 to 11, and reports of the total number of plants have ranged from 340 to 580.

Life cycle and ecology

Pollinated primarily by honeyeaters, the inflorescences appear from September to December. Prominent flowers, a red or pink colour, a straight style and a tubular perianth are features thought to promote pollination by birds. The structure of ''B. cuneata'''s flower, with the style end functioning as a pollen presenter, suggests that autogamous self-fertilisation must be common. This is countered, however, by protandry: pollen is released well before the pistil becomes receptive; usually by the time the pistil becomes receptive most of the pollen has either been transferred, or has lost its viability. This strategy is effective against individual flowers fertilising themselves, but does nothing to prevent geitonogamy: fertilisation of flowers by different flowers on the same plant. Because of the way flowers are clustered together in heads, this must be quite common, although whether it results in successful fruit set is another matter: isozyme studies have observed "intense selection against homozygotes", a fairly common outbreeding strategy in plants that set much seed.

Assessments of the mating system of this species have found that outcrossing rates vary between populations. Populations in relatively intact bushland have high outcrossing rates, but those in more disturbed environments are both more inbred on average, and more variable. 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 occasional visitors for pollination. The greatly reduced pollination rates means fewer outcrossing fertilisations on average, leading to less selection against inbred fertilisations; and the sporadic presence of pollinators leads to outcrossing variability.

No seed is set when pollinators are excluded

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