Banksia oligantha, commonly known as Wagin banksia, is an endangered species in the plant family Proteaceae endemic to south west Western Australia. It belongs to Banksia subg. Isostylis, a subgenus of three closely related Banksia species with dome-shaped heads as inflorescences, rather than characteristic Banksia flower spikes. A shrub or small tree up to 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.
Description
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 to . 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.
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 , and in width from , with a petiole 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 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 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 long, with a limb of . Perianth colour grades from red at the base to pale yellow at the limb. The styles are straight, 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 long by high by wide. Each follicle contains up to two winged seeds, from 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.
Taxonomy
Discovery and naming
Banksia oligantha was discovered by Ken Wallace of the Government of Western Australia'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 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.