Banksia prionotes, commonly known as acorn banksia or orange banksia, is a species of shrub or tree of the genus Banksia in the family Proteaceae. It is native to the southwest of Western Australia and can reach up to in height. It can be much smaller in more exposed areas or in the north of its range. This species has serrated, dull green leaves and large, bright flower spikes, initially white before opening to a bright orange. Its common name arises from the partly opened inflorescence, which is shaped like an acorn. The tree is a popular garden plant and also of importance to the cut flower industry.
Banksia prionotes was first described in 1840 by English botanist John Lindley, probably from material collected by James Drummond the previous year. There are no recognised varieties, although it has been known to hybridise with Banksia hookeriana. Widely distributed in south-west Western Australia, B. prionotes is found from Shark Bay (25° S) in the north, south as far as Kojonup (33°50′S). It grows exclusively in sandy soils, and is usually the dominant plant in scrubland or low woodland. Pollinated by birds, it provides food for a wide array of vertebrate and invertebrate animals in the autumn and winter months. It is an important source of food for honeyeaters (Meliphagidae), and is critical to their survival in the Avon Wheatbelt region, where it is the only nectar-producing plant in flower at some times of the year.
Description
Banksia prionotes grows as a tree up to high in southern parts of its distribution, but in northern parts it is usually a shorter tree or spreading shrub, reaching about in height; it diminishes in size as the climate becomes warmer and drier further north. It has thin, mottled grey, smooth or grooved bark, and tomentose young stems. The alternate dull green leaves are long, and wide, with toothed leaf margins made up of triangular lobes, and often a wavy surface.
Flowers occur in a typical Banksia flower spike, an inflorescence made up of hundreds of small individual flowers, or florets, densely packed around a cylindrical axis. B. prionotes has cream-coloured flowers with a bright orange limb that is not revealed until the flower fully opens. Known as anthesis, this process sweeps through the inflorescence from bottom to top over a period of days, creating the effect of a cream inflorescence that progressively turns bright orange. The old flower parts fall away after flowering finishes, revealing the axis, which may bear up to 60 embedded follicles. Oval or oblong in shape and initially covered in fine hairs, these follicles are from long and wide, and protrude from the cone. Inside, they bear two seeds separated by a brownish woody seed separator. The matte blackish seeds are wedge-shaped (cuneate) and measure long by wide with a membranous 'wing'.
The root system consists of a main sinker root, and up to ten lateral roots extending from a non-lignotuberous root crown. The main sinker root grows straight down to the water table; it may be up to long if the water table is that deep. Typically from in diameter immediately below the root crown, roots become gradually finer with depth, and may be less than half a centimetre (0.2 in) wide just above the water table. Upon reaching the water table, the sinker branches out into a network of very fine roots. The laterals radiate out horizontally from the base of the plant, at a depth of . They may extend over from the plant, and may bear secondary laterals; larger laterals often bear auxiliary sinker roots. Lateral roots seasonally form secondary rootlets from which grow dense surface mats of proteoid roots, which function throughout the wetter months before dying off with the onset of summer.
Taxonomy
Banksia prionotes was first published by English botanist John Lindley in the January 1840 issue of his A Sketch of the Vegetation of the Swan River Colony; hence the species' standard author citation is Banksia prionotes Lindl. He did not specify the type material upon which he based the species, but A Sketch of the Vegetation of the Swan River Colony is based primarily upon the collections of early settler and botanist James Drummond. A sheet of mounted specimens at the University of Cambridge Herbarium (CGE), labelled "Swan River, Drummond, 1839" and annotated "Banksia prionotes m" in Lindley's hand, has since been designated the lectotype. Lindley also made no mention of the etymology of the specific epithet, "prionotes", but it is assumed to be derived from the Ancient Greek prion ("saw") and -otes ("quality"), referring to the serrated leaf margins.