Banksia oligantha

Appearance

"Banksia oligantha" grows as a single-trunked small tree or as an erect shrub with few main stems. Reports of its maximum height vary from 3 m to 5 m. When not in flower it is said to look somewhat like "Banksia sessilis". 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.

Its leaves are deep green and glossy above, and a pale matte green below. They are roughly oval-shaped, but concave rather than lying 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, and in width from 0.4 to 2.0 cm, with a petiole 2 to 3 mm 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, the flowers occur in dome-shaped heads from 2.5 to 3 cm 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 long. 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. oligantha", the perianth is 21 to 22 mm long, with a limb of 3 to 3.5 mm. Perianth colour grades from red at the base to pale yellow at the limb. The styles are straight, 19 to 24 mm long, and uniformly cream.

Old flowers soon fall from the flower heads, revealing a woody dome with 1 to 6 follicles embedded in it. These are a mottled grey colour, smooth, and shortly furry. They are oval-shaped, measuring 14 to 19 mm long by 10 to 15 mm high by 8 to 9 mm wide. Each follicle contains up to two winged seeds, from 17 to 20 mm 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".

Naming

"Banksia oligantha" was discovered by Ken Wallace of the Government of Western Australia's Department of Conservation and Land Management in September 1984, during a survey of Wangeling Gully Nature Reserve, about 28 km 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. " appeared. The specific epithet "oligantha" derives from the Greek "oligo-" and "anthos", 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.

Distribution

"Banksia oligantha" occurs over a range of about 100 kilometres in southern parts of the Avon Wheatbelt region of the Southwest Botanical Province of Western Australia. 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 fell 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.

Status

"Banksia oligantha" is listed as an endangered species under the federal "Environment Protection and Biodiversity Conservation Act 1999", 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 rabbits, drought, the drift of aerosol chemicals from surrounding farmland, invasion by weeds, and rising salinity. Studies have shown it to be moderately susceptible to "Phytophthora cinnamomi" dieback.

Habitat

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.