Banksia prionotes

Banksia prionotes was first described in 1840 by English botanist John Lindley, probably from material collected by James Drummond the previous year.

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).

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.

[8] 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.

[3] 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.

The placement of B. prionotes in George's 1999 arrangement may be summarised as follows:[4] Since 1998, American botanist Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae, which includes Banksia.

'Waite Orange' is believed to be such a hybrid, having arisen by open pollination during a breeding experiment conducted at the Waite Agricultural Research Institute of the University of Adelaide in 1988.

For example, the first putative hybrids studied had a habit "like that of gigantic B. hookerana [sic]", having inherited the size of B. prionotes, together with B. hookeriana's tendency to branch from near the base of the trunk.

It grows among tall shrubland or low woodland, mostly in the swales and lower slopes of dunes, and shows a very strong preference for deep white or yellow sand.

[4][28][30] It is most common amongst the kwongan heath of the Geraldton Sandplains north of Jurien;[31] it has a fairly continuous distribution there, often as the dominant species, and extends inland to around the 350 mm isohyet.

[33] The soils east of the Darling Scarp are generally too heavy for this species, with the exception of some isolated pockets of deep alluvial or aeolian yellow sand.

[35] The latter hypothesis is supported by the recent expansion of B. prionotes along road verges of the Brand Highway, where fires are relatively rare.

[37] However, recent falls of the water table on the Swan Coastal Plain have seen B. prionotes replace the more water-loving Banksia littoralis in some areas that were previously flood-prone.

[28] Annual growth increases exponentially for the first eight years or so, but then slows down as resources are diverted into reproduction and the greater density of foliage results in reduced photosynthetic efficiency.

[5][40] The other common adaptation is the possession of cluster roots, which allow it to extract enough nutrients to survive in the oligotrophic soils in which it grows.

[5][40][41] The uptake of nutrient and water by the cluster roots peaks through winter and spring, but ceases when the upper layer of soil dries out in summer.

[39][40] When glutamine eventually reaches the leaves, it is broken down and used to synthesise protein and non-amide amino acids, such as aspartate, threonine, serine, glutamate, glycine, alanine and cystine.

Individual flowers open sequentially from bottom to top within each inflorescence, the rate varying with the time of day: more flowers open during the day than at night, with a peak rate of around two to three florets per hour during the first few hours of daylight, when honeyeater foraging is also at its peak.

As they probe for nectar, honeyeaters end up with large quantities of pollen on their beaks, foreheads and throats, some of which they subsequently transfer to other flowers.

[43] The structure of the Banksia flower, with the style end functioning as a pollen presenter, suggests that autogamous self-fertilisation must be common.

There is dispute, however, over whether this occurs in B. prionotes: one study claimed to have confirmed "protandrous development", yet recorded high levels of stigmatic receptivity immediately after anthesis, and long pollen viability,[43] observations that are not consistent with protandry.

In strongly serotinous species, the old florets are retained on the cones, where they function as fire fuel, helping to ensure that follicles reach temperatures sufficient to trigger seed release.

This adaptation ensures that seed release following fire is delayed until the onset of rain, when germination and seedling survival rates are higher.

It is highly susceptible to Phytophthora cinnamomi dieback;[53][54] wild populations are harvested commercially by the cut flower industry;[9] and some of its range is subject to land clearing for urban or agricultural purposes.

[30] It nonetheless has high conservation importance in at least one context: it is a keystone mutualist in the Avon Wheatbelt, where it is the only source of nectar during a critical period of the year when no other nectar-producing plant is in flower.

Although currently in near-pristine and static condition, it is considered at risk due to a large number of threatening processes, including land clearing, landscape fragmentation, rising soil salinity, grazing pressure, competition with weeds, changes to the fire regime, rubbish dumping, and P. cinnamomi dieback.

[58][59] Described as "an outstanding ornamental species" by ASGAP,[10] its brightly coloured, conspicuous flower spikes make B. prionotes a popular garden plant.

A low growing dwarf form which reaches 1 m (3.3 ft) high is available in Western Australia, sold as "Little Kalbarri Candles".

[62] As such it is one of the most popular banksias for cut flower production, with commercial crops grown in Israel, Victoria, South Australia and Hawaii.

A gnarled, spreading tree about three metres high, on an otherwise treeless plain with low shrubs
A more gnarled shorter tree or shrub is typical in the north of the range.
a large spreading tree about ten metres high in front of a slightly smaller tree, in grassland
A taller, more upright habit, with an open canopy, is typical in the south of the range
A large, dense, shrubby tree, about three metres high and wide
A hybrid, B. prionotes × hookeriana , growing on a roadside near Walkaway . The large size, consistent with B. prionotes , together with the narrow leaves of B. hookeriana , are diagnostic.
Foliage of B. menziesii × prionotes , in cultivation, Kings Park, Perth, Western Australia
A map of the biogeographic regions of Western Australia, showing the range of Banksia prionotes. The map shows a continuous distribution from the northern tip of the Geraldton Sandplains, south along the west coast to around Perth, and continuing south further inland to the southern limit of the Jarrah Forests region. There are also discontinuous occurrence shown at Shark Bay in the north, and in the southeast around Jerramungup.
Distribution
Closeup of inflorescence, showing a bee is feeding at the junction of white unopened buds and orange opened flowers
Close-up of inflorescence, with a European honey bee feeding at the plane of anthesis . Insects are apparently ineffective pollinators.
The charred trunk of a large burnt tree, with seedlings arising out of the bare sand around it
After a bushfire. Fire has killed the maternal tree, but has also triggered the release of seed, ensuring population recovery.
A small spreading shrub about 40 cm (15.5 in) high, with several inflorescences in early bud, growing in sand
Dwarf form in cultivation, with inflorescences in late bud