Banksia attenuata

Species of plant in the family Proteaceae found across much of the southwest of Western Australia
speciesbox
| name = Candlestick banksia or biara
| image = Banksia attenuata Marg River email. jpg
| image caption = B. attenuata, Margaret River
| status = VU
| status system = IUCN3.1
| status ref =
| image alt = A yellow cylindrical flower spike emerging from dark green foliage on the left, and a greenish cylindrical flower spike emerging from dark green foliage on the right
| taxon = Banksia attenuata
| authority = R. Br. | synonyms ref = is a species of plant in the family Proteaceae. Commonly a tree, it reaches high, but it is often a shrub in drier areas high. It has long, narrow, serrated leaves and bright yellow inflorescences, or flower spikes, held above the foliage, which appear in spring and summer. The flower spikes age to grey and swell with the development of the woody follicles. The candlestick banksia is found across much of the southwest of Western Australia, from north of Kalbarri National Park down to Cape Leeuwin and across to Fitzgerald River National Park. English botanist John Lindley had named material collected by Australian botanist James Drummond Banksia cylindrostachya in 1840, but this proved to be the same as the species named Banksia attenuata by Scottish botanist Robert Brown 30 years earlier in 1810, and thus Brown's name took precedence. Within the genus Banksia, the close relationships and exact position of B. attenuata is unclear. The candlestick banksia is pollinated by and provides food for a wide array of animals in summer months. Several species of honeyeater visit the flower spikes, as does the honey possum, which has an important role as a pollinator. It regenerates from bushfire by regrowing from its woody base, known as a lignotuber, or from epicormic buds within its trunk. It can have a lifespan of 300 years. It has been widely used as a street tree and for amenities planting in urban Western Australia, though its large size generally precludes use in small gardens. A dwarf form is commercially available in nurseries.

Banksia attenuata is generally encountered as a tree up to tall. In the north of its range as the climate becomes warmer and drier, it is often a stunted multistemmed shrub 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 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 long and 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 (flower spikes) occur from spring into summer and are up wide and up to tall. and another in the Fitzgerald River National Park yielded a count of 1720 (± 76) 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.

Banksia attenuata was first collected by Robert Brown from King George Sound in December 1801 and published by him in 1810. The specific epithet is the Latin adjective attenuatus "narrowed", and refers to the leaves narrowing towards the base. The species has had a fairly uneventful taxonomic history. It has only two synonyms, and no subspecies or varieties have been published; Australian botanist Alex George reviewed the variation in form in the species and felt that the tree and shrub forms differed only in size and hence were not distinct enough to represent separate taxa. In 1891, Otto Kuntze rejected the generic name Banksia L. f., on the grounds that the name Banksia had previously been published in 1776 as Banksia J. R. Forst & G. Forst, referring to the genus now known as Pimelea. Kuntze proposed Sirmuellera as an alternative, referring to this species as Sirmuellera attenuata. This application of the principle of priority was largely ignored by Kuntze's contemporaries, and Banksia L. f. was formally conserved and Sirmuellera rejected in 1940. Common names include slender banksia, candle banksia, and candlestick banksia. Piara (alternately spelled biara) is an aboriginal name from the Melville region of Perth. The relationships of Banksia attenuata within the genus are unclear. When Carl Meissner published his infrageneric arrangement of Banksia in 1856, he placed B. attenuata in section Eubanksia because its inflorescence is a spike rather than a domed head, and in series Salicinae, a large series that is now considered quite heterogeneous. In 1981, George published a revised arrangement that placed B. attenuata in the subgenus Banksia because of its flower spike, section Banksia because its styles are straight rather than hooked, and the series Cyrtostylis, a large and rather heterogenous series of twelve species. He conceded its large emarginate cotyledons (having a notch in their apex) were quite different from other members, and that it had similarities in flower architecture to another anomalous member B. elegans. He felt B. attenuata to have affinities to B. lindleyana and B. media. Questioning the emphasis on cladistics in Thiele and Ladiges' arrangement, George published a slightly modified version of his 1981 arrangement in his 1999 treatment of Banksia for the Flora of Australia series of monographs. To date, this remains the most recent comprehensive arrangement. The placement of B. attenuata in George's 1999 arrangement may be summarised as follows: An Eocene fossil cone named Banksia archaeocarpa, around 50 million years old, resembles that of B. attenuata. Early in 2007, Mast and Thiele rearranged the genus Banksia by merging Dryandra into it, and published B. subg. Spathulatae for the taxa having spoon shaped cotyledons; thus B. subg. Banksia was redefined as encompassing taxa lacking spoon shaped cotyledons. They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, if Mast and Thiele's nomenclatural changes are taken as an interim arrangement, then B. attenuata is placed in B. subg. Banksia.

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 (with an outlying population in Zuytdorp National Park) 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 (clay based) soils, and is hence only found in sandy pockets. Bearing epicormic buds and a lignotuber, B. attenuata is one of the latter group, with follicles that may open spontaneously or by fire. 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 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 (which were kept dry) 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 (instead of dryer summer), 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, 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 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 are 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 away (similar rates to Banksia hookeriana, the seed of which only weighs half as much). The mechanism for this is unclear, although Byron Lamont has proposed the Carnaby's black cockatoo (Calyptorhynchus latirostris) 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. A field study in the Fitzgerald River National Park where inflorescences were enclosed in mesh fine enough to keep out vertebrates and invertebrates as small as the honey bee (Apis mellifera) showed that follicles still developed, indicating that small invertebrates were able to cross pollinate the species. Other pollinating invertebrates recorded include ants and dragonflies. Many bird species were recorded by the national Banksia Atlas survey, including the New Holland honeyeater (Phylidonyris novaehollandiae), brown honeyeater (Lichmera indistincta), singing honeyeater (Lichenostomus virescens), western spinebill (Acanthorhynchus superciliosus), twenty eight parrot (Barnardius zonarius semitorquatus) and red tailed black cockatoo (Calyptorhynchus banksii). At a site near Jandakot, short billed black cockatoos were observed selecting immature infructescences which bore signs of infestation by the weevil Alphitopis nivea, the larvae of which tunnel in banksia spikes and eat the seed. They extract the larvae and drop the cones. A 1978 field study conducted around Albany found the honey possum (Tarsipes rostratus) was a major pollinator of Banksia attenuata, both feeding directly on the pollen and drinking the nectar. The flower structure is suited to passing pollen onto the possum as it feeds, unlike honeyeaters whose bills are too long for this to occur readily. Coupled with the flower spike's musky odour, these findings suggest Banksia attenuata is highly adapted to be pollinated primarily by this mammal species. Furthermore, Petroc Sumner and colleagues have investigated the cone photoreceptor cells of honey possums and compared them with the colour changes of B. attenuata. They found that the possum is trichromatic (like humans and possibly many marsupials) and propose that its L (long wavelength) cones help it discern B. attenuata flower spikes, and the M (or medium wavelength) cones could help it distinguish ripe inflorescences with nectar from recently finished spikes (a difficult task for human vision). There is some evidence for other mammals as pollinators; B. attenuata like pollen was recovered from museum skins of dunnarts (Sminthopsis spp.) and pygmy possums (Cercartetus spp. ), and the sugar glider (Petaurus breviceps) visited flower spikes in captivity. All banksias have developed proteoid or cluster roots in response to the nutrient poor conditions of Australian soils (particularly lacking in phosphorus). These have been measured in Eneabba extending to a depth of 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 (winter spring). 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 (Ehrharta calycina and Pelargonium capitatum) 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 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.

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. Seedlings are highly vulnerable to damping off. 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.