Banksia sessilis

Species of plant of Western Australia

Banksia sessilis, commonly known as parrot bush, is a species of shrub or tree in the plant genus Banksia of the family Proteaceae. It had been known as Dryandra sessilis until 2007, when the genus Dryandra was sunk into Banksia. The Noongar peoples know the plant as budjan or butyak. Widespread throughout southwest Western Australia, it is found on sandy soils over laterite or limestone, often as an understorey plant in open forest, woodland or shrubland. Encountered as a shrub or small tree up to in height, it has prickly dark green leaves and dome shaped cream yellow flowerheads. Flowering from winter through to late spring, it provides a key source of food—both the nectar and the insects it attracts—for honeyeaters in the cooler months, and species diversity is reduced in areas where there is little or no parrot bush occurring. Several species of honeyeater, some species of native bee, and the European honey bee seek out and consume the nectar, while the long billed black cockatoo and Australian ringneck eat the seed. The life cycle of Banksia sessilis is adapted to regular bushfires. Killed by fire and regenerating by seed afterwards, each shrub generally produces many flowerheads and a massive amount of seed. It can recolonise disturbed areas, and may grow in thickets. Banksia sessilis has a somewhat complicated taxonomic history. It was collected from King George Sound in 1801 and described by Robert Brown in 1810 as Dryandra floribunda, a name by which it was known for many years. However, Joseph Knight had published the name Josephia sessilis in 1809, which had precedence due to its earlier date, and the specific name was formalised in 1924. Four varieties are recognised. It is a prickly plant with little apparent horticultural potential; none of the varieties are commonly seen in cultivation. A profuse producer of nectar, B. sessilis is valuable to the beekeeping industry.

Banksia sessilis grows as an upright shrub or small tree up to high, without a lignotuber. In most varieties, new stems are covered in soft, fine hairs that are lost with maturity; but new stems of B. sessilis var. flabellifolia are usually hairless. Leaves are blue green or dark green. Their shape differs by variety: in var. cygnorum and var. flabellifolia they are wedge shaped, with teeth only near the apex; in var. cordata they are wedge shaped, but with teeth along the entire margin; and in var. sessilis they are somewhat broader at the base, sometimes almost oblong in shape. Leaf size ranges from in length, and in width. They may be sessile (that is, growing directly from the stem without a petiole) or on a petiole up to long. The inflorescences are cream or yellow, and occur in domed heads wide, situated at the end of a stem. Each head contains from 55 to 125 individual flowers, surrounded at the base by a whorl of short involucral bracts. As with most other Proteaceae, individual flowers consist of a tubular perianth made up of four united tepals, and one long wiry style. The style end is initially trapped inside the upper perianth parts, but breaks free at anthesis. In B. sessilis the perianth is straight, long, and pale yellow. The style is slightly shorter, also straight, and cream coloured. Thus in B. sessilis, unlike many other Banksia species, the release of the style at anthesis does not result in a showy flower colour change. and Menzies' journal indicates that he collected over a wide area, visiting a different location every day from 29 September to 8October. In addition to B. sessilis, Menzies collected plant material of B. pellaeifolia, and seeds of at least four more Banksia species. This was therefore an important early collection for the genus, only seven species of which had previously been collected. Menzies' seed specimens were sent to England from Sydney in 1793, but his plant material remained with him for the duration of the voyage, during which some material was lost. On his return to England in 1795, the surviving specimens were deposited into the herbarium of Sir Joseph Banks, where they lay undescribed for many years. but neither Brown's nor Good's diary can be used to assign a precise location or date for their discovery of the species. Good also made a separate seed collection, which included B. sessilis, and the species was drawn by Bauer. Like nearly all of his field drawings of Proteaceae, Bauer's original field sketch of B. sessilis was destroyed in a Hofburg fire in 1945. A painting based on the drawing survives, however, at the Natural History Museum in London. On returning to England in 1805, Brown began preparing an account of his Australian plant specimens. In September 1808, with Brown's account still far from finished, Swedish botanist Jonas Dryander asked him to prepare a separate paper on the Proteaceae so he could use the genera erected by Brown in a new edition of Hortus Kewensis. Brown immediately began a study of the Proteaceae, and in January 1809 he read to the Linnean Society of London a monograph on the family entitled On the Proteaceae of Jussieu. Among the eighteen new genera presented was one that Brown named Josephia in honour of Banks. Brown's paper was approved for printing in May 1809, but did not appear in print until March the following year. In the meantime, Joseph Knight published On the cultivation of the plants belonging to the natural order of Proteeae, which appeared to draw heavily on Brown's unpublished material, without permission, and in most cases without attribution. The etymology of the specific epithet was not explicitly stated, but it is universally accepted that it comes from the Latin sessilis (sessile, stalkless), in reference to the sessile leaves of this species. As there were then no firm rules pertaining to priority of publication, Brown's name was accepted, and remained the current name for over a century. Another significant early collection was the apparent discovery of the species at the Swan River in 1827. In that year, the colonial botanist of New South Wales Charles Fraser visited the area as part of an exploring expedition under James Stirling. Among the plants Fraser found growing on the south side of the river entrance was "a beautiful species of Dryandra", which was probably this species. Over the course of the 19th century, the principle of priority in naming gradually came to be accepted by botanists, as did the need for a mechanism by which names in current usage could be conserved against archaic or obscure prior names. By the 1920s, Dryandra R. Br. was effectively conserved against Josephia Knight; a mechanism for formal conservation was put in place in 1933. Brown's specific name, however, was not conserved, and Karel Domin overturned Dryandra floribunda R. Br. by transferring Knight's name into Dryandra as Dryandra sessilis (Knight) Domin in 1924. This name was current until 2007, when all Dryandra species were transferred into Banksia by Austin Mast and Kevin Thiele. The full citation for the current name is thus Banksia sessilis (Knight) A. R. Mast & K. R. Thiele.

The first common names for this species were literal translations of the scientific names. When published as Josephia sessilis in 1809, it was given the common name sessile Josephia. In Australia, the names prickly banksia and shaving brush flower were offered up by Emily Pelloe in 1921, the latter because "when in bud the flower very much resembles a shaving brush". Shaving brush flower was still in use as late as the 1950s. The name holly leaved dryandra was used when the plant was featured as part of a series of articles in the Western Mail of 1933–34, and this was taken up by William Blackall in 1954, and was still in use as late as 1970. Meanwhile, Gardner used the name parrot bush in 1959, by which the species was already "well known to bee keepers". This name was widely adopted, and since 1970 has been in almost exclusive usage. However, Abbott sources these names to George Fletcher Moore's 1842 A Descriptive Vocabulary of the Language of the Aborigines, which in fact attributes these names to the species Dryandra fraseri (now Banksia fraseri). It is unclear whether Abbott has corrected Moore's error, or introduced an error of his own.

Brown's 1810 monograph did not include an infrageneric classification of Dryandra, In 1830, however, he introduced the first taxonomic arrangement of Dryandra, placing D. floribunda in section Dryandra verae along with most other species, because its follicles contain a single seed separator. Dryandra verae was renamed Eudryandra by Carl Meissner in 1845. Eleven years later Meissner published a new arrangement, retaining D. floribunda in D. sect. Eudryandra, and further placing it in the unranked subgroup § Ilicinae, because of the similarity of its leaves to those of Ilex (holly). In 1870, George Bentham published a revised arrangement in his Flora Australiensis. Bentham retained section Eudryandra, but abandoned almost all of Meissner's unranked groups, including § Ilicinae. D. floribunda was instead placed in D. ser. Floribundae along with four other species with small, mostly terminal flowers, left exposed by their having unusually short floral leaves. Bentham's arrangement stood for over a hundred years, eventually replaced in 1996 by the arrangement of Alex George. Section Eudryandra was promoted to subgenus rank, but replaced by the autonym D. subg. Dryandra. D. sessilis, as this species was now called, was retained in D. ser. Floribundae, but alone, as the series was redefined as containing only those taxa that apparently lack floral bracts altogether. and 2005 amendments, may be summarised as follows:

Dryandra (now Banksia ser. Dryandra)
D. subg. Dryandra
D. ser. Floribundae
D. sessilis (now B. sessilis)
D. sessilis var. sessilis (now B. sessilis var. sessilis)
D. sessilis var. flabellifolia (now B. sessilis var. flabellifolia)
D. sessilis var. cordata (now B. sessilis var. cordata)
D. sessilis var. cygnorum (now B. sessilis var. cygnorum)
D. ser. Armatae
D. ser. Marginatae
D. ser. Folliculosae
D. ser. Acrodontae
D. ser. Capitellatae
D. ser. Ilicinae
D. ser. Dryandra
D. ser. Foliosae
D. ser. Decurrentes
D. ser. Tenuifoliae
D. ser. Runcinatae
D. ser. Triangulares
D. ser. Aphragma
D. ser. Ionthocarpae
D. ser. Inusitatae
D. ser. Subulatae
D. ser. Gymnocephalae
D. ser. Plumosae
D. ser. Concinnae
D. ser. Obvallatae
D. ser. Pectinatae
D. ser. Acuminatae
D. ser. Niveae
D. subg. Hemiclidia
D. subg. Diplophragma

George's arrangement remained current until 2007, when Austin Mast and Kevin Thiele transferred Dryandra into Banksia. They also published B. subg. Spathulatae for the Banksia taxa having spoon shaped cotyledons, thus redefining B. subg. Banksia as comprising those that do not. They were not ready, however, to tender an infrageneric arrangement encompassing Dryandra, so as an interim measure they transferred Dryandra into Banksia at series rank. This minimised the nomenclatural disruption of the transfer, but also caused George's rich infrageneric arrangement to be set aside. Thus under the interim arrangements implemented by Mast and Thiele, B. sessilis is placed in B. subg. Banksia, ser. Dryandra.|alt=A map of the biogeographic regions of Western Australia, showing the range of Banksia sessilis. It occupies the southwestern corner of Australia.]] Banksia sessilis is endemic to the Southwest Botanical Province, a floristic province renowned as a biodiversity hotspot, located in the southwest corner of Western Australia. This area has a Mediterranean climate, with wet winters and hot, dry summers. B. sessilis occurs throughout much of the province, ranging from Kalbarri in the north, south to Cape Leeuwin, east along the south coast as far as Bremer Bay, and inland to Wongan Hills and Kulin. Nothing is known of the conditions that affect its distribution, as its biogeography is as yet unstudied. An assessment of the potential impact of climate change on this species found that its range is likely to contract by half in the face of severe change, but unlikely to change much under less severe scenarios.

The nectar of B. sessilis is an important component of the diet of several species of honeyeater. In one study, B. sessilis was found to be the main source of nectar for all six species studied, namely the tawny crowned honeyeater (Gliciphila melanops), white cheeked honeyeater (Phylidonyris niger), western spinebill (Acanthorhynchus superciliosus), brown honeyeater (Lichmera indistincta), brown headed honeyeater (Melithreptus brevirostris), and black honeyeater (Certhionyx niger). Moreover, B. sessilis played an important role in their distributions, with species that feed only on nectar occurring only where B. sessilis occurs, and remaining for longest at sites where B. sessilis is most abundant. Other honeyeaters that have been recorded feeding on B. sessilis include the red wattlebird (Anthochaera carunculata), western wattlebird (A. lunulata), and New Holland honeyeater (Phylidonyris novaehollandiae). Furthermore, a study of bird species diversity in wandoo woodland around Bakers Hill found that honeyeater species and numbers were much reduced in forest that lacked a Banksia sessilis understory; the plant is a key source of nectar and insects during the winter months. A field study in jarrah forest 9 km south of Jarrahdale, where B. sessilis grows in scattered clumps, found that western wattlebirds and New Holland honeyeaters sought out groups of plants with the greatest numbers of new inflorescences, particularly those one or two days after anthesis, where nectar yield was highest. The birds likely recognises these by visual clues. Banksia sessilis is also a source of food for the Australian ringneck (Barnardius zonarius), and the long billed black cockatoo (Calyptorhynchus baudinii), which tear open the follicles and consume the seeds. The introduced European honey bee (Apis mellifera) has also been observed feeding on B. sessilis, as have seven species of native bee, comprising four species of Hylaeus (including the banksia bee H. alcyoneus), two of Leioproctus, and a Lasioglossum.

Honeyeaters are clearly the most important pollination vector, as inflorescences from which honeyeaters are excluded generally do not set any fruit. Moreover, honeyeaters have been observed moving from tree to tree with significant loads of B. sessilis pollen on their foreheads, beaks and throats, having acquired it by brushing against pollen presenters while foraging for nectar; experiments have shown that some of this pollen may be subsequently deposited on stigmas during later foraging. The flowers of B. sessilis have adaptations that encourage outcrossing. Firstly, they are protandrous: a flower's pollen is released around 72 hours before it becomes itself receptive to pollen, by which time around half of its pollen has lost its viability. Secondly, the period of maximum nectar production closely matches the period during which the flower is sexually active, so honeyeaters are enticed to visit at the most opportune time for pollination. This has proven an effective strategy: almost all pollen is removed within two to three hours of presentation. In addition, honeyeaters tend to move between inflorescences on different plants, rather than between inflorescences on the same plant, at least in high density sites. These factors combine to make it fairly unusual for a flower to be fertilised by its own pollen. "weakly serotinous" and "non serotinous". Regardless of the terminology used, the massive spontaneous seed output of B. sessilis is its primary survival strategy, and is so effective the species has a reputation as an excellent coloniser. Seeds of B. sessilis are short lived, and must germinate in the winter following their release, or they die.

Banksia sessilis is highly susceptible to dieback caused by the introduced plant pathogen Phytophthora cinnamomi, a soil borne water mould that causes root rot; in fact it is so reliably susceptible it is considered a good indicator species for the presence of the disease. Most highly susceptible species quickly become locally extinct in infected areas, and in the absence of hosts the disease itself eventually dies out. However, B. sessilis, being an aggressive coloniser of disturbed and open ground, often colonises old disease sites. The new colonies are themselves infected, and thus P. cinnamomi survives at these sites indefinitely. but has been shown to reduce pollen fertility: one study recorded fertility reductions of up to 50%, and, in a separate experiment, fertility reductions that persisted for more than a year. Infection of coastal stands of B. sessilis by the fungus Armillaria luteobubalina has also been recorded. The apparent infection rate of 0.31 is quite slow compared to the progress of other Armillaria species through pine plantations.

It is not known whether the seed collection sent to the Royal Botanic Gardens, Kew, by Menzies in 1793 included seeds of B. sessilis, but if it did then it did not germinate. and in 1810 it was reported in the second edition of Hortus Kewensis as flowering "most part of the Year". including a painting of B. sessilis. These were subsequently republished in Charles Gardner's 1935 West Australian Wild Flowers. One of the first published colour photographs of the species appeared in William Blackall's 1954 How to know Western Australian wildflowers, but this publication was restricted to plant identification. Possibly the first published information on the cultivation of Dryandra appeared in the magazine Australian Plants in June and September 1961. From its inception in 1962, the Kings Park and Botanic Garden undertook extensive research into the cultivation of native plants, resulting in two early publications that mentioned the cultivation potential of B. sessilis. Five years later, Arthur Fairall published West Australian native plants in cultivation. This presented largely the same information as Beard's catalogue, adding only that the species flowers well in its third season.

According to current knowledge, B. sessilis is an extremely hardy plant that grows in a range of soils and aspects, so long as it is given good drainage, Germination takes about five or six weeks, and plants may take two years to flower.