Candlestick banksia or biara

Appearance

''Banksia attenuata'' is generally encountered as a tree up to 10 m tall. In the north of its range as the climate becomes warmer and dryer, it is often a stunted multistemmed shrub 0.4 to 2 m tall. Both forms occur in the vicinity of Hill River but there is otherwise a marked demarcation.


In the Wheatbelt and east of the Stirling Range, it is a stunted tree. Tree forms have a solid trunk, generally wavy or bent, with 1–2 cm thick crumbly orange-grey bark which is a red-brown underneath. It regenerates from fire via lignotuber or epicormic buds from its fire-tolerant trunk. It has long narrow shiny green linear leaves 4 to 27 cm long and 0.5 to 1.6 cm wide. The leaf margins have v- or u-shaped serrations along their length. The new growth is a pale grey-green, and occurs mainly in the late spring and summer, often after flowering. The brilliant yellow inflorescences occur from spring into summer and are up 5 cm wide and up to 25–30 cm tall. They are made up of many small individual flowers; a study at Mount Adams 330 km north of Perth revealed a count of 1933 flowers per inflorescence, and another in the Fitzgerald River National Park yielded a count of 1720 flowers. Anthesis proceeds up the flower spike over about 10 to 20 days, and is asynchronous. That is, a plant produces flower spikes over a several week period and will thus have spikes at different stages of development over the flowering season.

Often bright green in bud stage, they are terminal, occurring at the ends of one- to three-year-old branches, and displayed prominently above the foliage. The smell of the open flowers has been likened to a peppery Shiraz wine. Over time, the spikes fade to brown and then grey, and the individual flowers shrivel and lie against the spikes. This coincides with the development of dark furry oval follicles, which measure 2–3.5 cm long, 1–1.5 cm high, and 1.4–2 cm wide. However, only a very small percentage of flowers develop into follicles; the field study at Mount Adams yielded a count of 3.6 ± 1.2 per cone. The follicles develop and mature over seven to eight months, from February to December, while seed development occurs over four months from September to December.

Distribution

The most widely distributed of all western banksias, ''Banksia attenuata'' occurs across a broad swathe of southwest of Western Australia, from Kalbarri National Park and the Murchison River southwards right to the southwestern corner of the state at Augusta and Cape Leeuwin, and then eastwards across the south to the western edge of Fitzgerald River National Park. Along the eastern border northwards it is found at Lake Grace, Lake Magenta north of Jerramungup, and the Wongan Hills. It is restricted to various sandy soils, including white, yellow or brown sands, and sand over either laterite or limestone. It forms an important component of open ''Eucalyptus'' woodland as a dominant or understory tree or tall shrub. To the north, it is a shrubby component of shrubland. It does not grow on heavy soils, and is hence only found in sandy pockets. Within open woodland, it is found alongside ''B. menziesii'', ''B. ilicifolia'', ''B. prionotes'', ''Allocasuarina fraseriana'', ''Eucalyptus marginata'', or ''E. gomphocephala''. The annual rainfall within its distribution varies from 300 to 900 mm .

Habitat

The most widely distributed of all western banksias, ''Banksia attenuata'' occurs across a broad swathe of southwest of Western Australia, from Kalbarri National Park and the Murchison River southwards right to the southwestern corner of the state at Augusta and Cape Leeuwin, and then eastwards across the south to the western edge of Fitzgerald River National Park. Along the eastern border northwards it is found at Lake Grace, Lake Magenta north of Jerramungup, and the Wongan Hills. It is restricted to various sandy soils, including white, yellow or brown sands, and sand over either laterite or limestone. It forms an important component of open ''Eucalyptus'' woodland as a dominant or understory tree or tall shrub. To the north, it is a shrubby component of shrubland. It does not grow on heavy soils, and is hence only found in sandy pockets. Within open woodland, it is found alongside ''B. menziesii'', ''B. ilicifolia'', ''B. prionotes'', ''Allocasuarina fraseriana'', ''Eucalyptus marginata'', or ''E. gomphocephala''. The annual rainfall within its distribution varies from 300 to 900 mm .Like many plants in south-west Western Australia, ''B. attenuata'' is adapted to an environment in which bushfire events are relatively frequent. Most ''Banksia'' species can be placed in one of two broad groups according to their response to fire: ''reseeders'' are killed by fire, but fire also triggers the release of their canopy seed bank, thus promoting recruitment of the next generation; ''resprouters'' survive fire, resprouting from a lignotuber or, more rarely, epicormic buds protected by thick bark. Bearing epicormic buds and a lignotuber, ''B. attenuata'' is one of the latter group, with follicles that may open spontaneously or by fire.

It is moderately serotinous, storing only one tenth the number of seeds in its seed bank as the reseeding ''B. hookeriana'' with which it coexists on sand dunes in scrub at Eneabba north of Perth. Even then, many of its follicles do not release seed after a fire, but instead after successive autumn rains. An experiment simulating wet weather following a fire saw a series of ''Banksia attenuata'' cones with follicles subjected to twice weekly immersions in water after being heated in a ring Bunsen flame to around 500–600 °C for two minutes. Cones that had been exposed to water for more weeks had more seed released from follicles over time; around 40% released at three weeks, increasing steadily to almost 90% at ten weeks, compared with a series of controls of which fewer than 10% of seed released. Thus, the seed remains in the follicles until successive rains result in seed dispersal in the wetter winter , increasing the chance of survival. After the follicle is split, the seed and separator are exposed to the elements. The wings of the woody separator are hygroscopic, and move together when wet, and spread and curl apart when dry. The seed is gradually drawn out by the movement with each wetting.

Once released, seed germinates at temperatures between 15 and 20 °C to optimise timing with autumn and winter rains and hence maximise chance of survival. Still, many seedlings die off in the hot and dry summer months. Seedling survival for the species is lower than for banksias which regenerate by seeding over time. Despite this, the longevity of mature plants allows for maintenance of population until favourable years enable better survival of young plants. As they mature, plants are less likely to perish, and estimated to live for 300 years or more. Analyzing the seed bank and longitudinal results over fifteen years on the Eneabba sandplain showed that ''B. attenuata'' would become more abundant over time with fire intervals averaging between 6 and 20 years, peaking with intervals around 10 to 12 years, compared with longer intervals for the reseeders ''B. hookeriana'' and ''B. prionotes''. Placed against its rivals, ''B. attenuata'' would be dominant between 8 and 10 or 11 years, but at longer intervals is outcompeted by ''B. hookeriana''. Variability in the timing between fires allows all three species to coexist. Exaggerated good and bad weather conditions favours ''B. attenuata'' over the reseeding species, which suffer more.

Despite having relatively heavy seed, seed from ''Banksia attenuata'' has a high rate of long distance dispersal. A genetic study of populations in Eneabba showed that over 5% of plants had originated up to 2.6 km away . The mechanism for this is unclear, although Byron Lamont has proposed the short-billed black cockatoo as a vector; the species seeks out ''Banksia attenuata'' cones after bushfire, possibly because the large seeds and greater chance of grubs in the cone make them more nutritious. Flowering has been recorded one to two years after a bushfire.
y of the bark. Another order, the Physarales, was unusually rare—other studies have demonstrated that the order is typically abundant on the bark of various species of tree around the world.


All banksias have developed proteoid or cluster roots in response to the nutrient-poor conditions of Australian soils . These have been measured in Eneabba extending to a depth of 15 cm below the soil surface. The plant develops masses of fine lateral roots which form a mat-like structure underneath the soil surface, and enable it to extract nutrients as efficiently possible out of the soil. A study of three co-occurring species in ''Banksia'' woodland in southwestern Australia—''Banksia menziesii'', ''B. attenuata'' and ''B. ilicifolia''—found that all three develop fresh roots in September after winter rainfall, and that the bacteria populations associated with the root systems of ''B. menziesii'' differ from the other two, and that they also change depending on the age of the roots. Another study on root architecture of ''Banksia hookeriana'', ''B. menziesii'' and ''B. attenuata'' found the overall structure of all three to be similar, with proteoid mats more active and growing in wetter months . Plants send out several sinker roots which descend to reach the water table, and the original tap root may or may not have died off. Along with ''B. menziesii'', ''B. attenuata'' is a facultative phreatophyte. The two species are less strictly tied to the water table and hence able to grow in a wider variety of places within ''Banksia'' woodland habitat around Perth than the co-occurring ''B. ilicifolia'' and ''B. littoralis''. A study at a rehabilitation site on a sand mine north of Perth found that the broadleaved species ''B. attenuata'' and ''B. hookeriana'' were harder to establish than the fine-leaved ''B. leptophylla'' there, due to increased impedance of the disturbed soil. Analysis of native plant species at a remnant of banksia woodland in suburban Perth which had been invaded by two herbaceous weed species found increased phosphorus levels in native foliage. Although ''B. attenuata'' leaves did not have increased phosphorus, they did have reduced levels of manganese—an element which is absorbed into the plant by its proteoid roots, the formation of which can be inhibited by raised levels of phosphorus.

In a 1985 study inoculating cultivated plants, ''Banksia attenuata'' showed moderate to high susceptibility to ''Phytophthora cinnamomi'' dieback; and at least some field and cultivation evidence points to it being highly susceptible. ''P. cinnamomi'' spreads from plant to plant via lateral roots, advancing at a rate of around a metre a year. The symptoms of infection in ''Banksia attenuata'' include yellowing of the leaves in the tree crown, and lesions at the base of the trunk. The red healthy roots become discoloured brown. A study of ''Banksia attenuata'' woodland 400 km southeast of Perth across 16 years and following a wave of ''P. cinnamomi'' infestation showed that ''B. attenuata'' populations still existed but were significantly reduced in diseased areas. Injecting a solution of phosphite into the trunks of affected ''B. attenuata'' trees at a disease front in ''Banksia'' woodland can delay morbidity from dieback for five years. Injecting and spraying phosphite also reduces the rate of spread of a dieback front for around five years. A bushfire did not influence this slowing. A 2003 study found that drenching the soil with 0.50 mM benzoic acid significantly reduced the size of ''P. cinnamomi'' lesions. Research into dieback in Western Australia has identified a new species, ''P. multivora'', isolated from ailing eucalypts and ''B. attenuata'' in 2009.

Cultural

The well-displayed bright yellow spikes are an attractive feature, with shrubby dwarf forms more versatile horticulturally. All forms of ''Banksia attenuata'' require good drainage, sandy soil and a sunny position to do well, with a pH between 5.5 and 7.0. They are sensitive to dieback, and do not fare well in humid climates. Seeds do not require any treatment, and take 16 to 49 days to germinate. Seedlings are highly vulnerable to damping off. Plants take from four to six years to flower from seed. There has been little success with other methods of improving adaptability to humid climates such as grafting.
-->
Flower spikes in late bud are used in the cut flower industry, primarily in Western Australia.

Aboriginal people, particularly the Nyoongar and Yamatji, placed the flower spike in a paperbark-lined hole filled with water to make a sweet drink. Both this species and ''B. aemula'' have been credited with the inspiration behind May Gibbs' Big Bad Banksia Men; this species was familiar to Gibbs in her childhood and likely gave her the initial inspiration, although the depictions resemble the latter species. Artist Marianne North produced a highly regarded painting of ''B. attenuata'' during her stay in Australia in 1880–1881.