Banksia verticillata

Shrub of southwest Western Australia
Speciesbox
|name = Granite banksia
|image = Banksia verticillata and New Holland Honeyeater. JPG
|image alt = A New Holland honeyeater feeds on one of several cylindrical golden flower spikes partly hidden by foliage. |status = VU
|status system = EPBC
|status ref = It may be much lower or even adopt a prostrate habit in highly exposed areas which are blasted by high wind, or occasionally grow as a single trunked tree. The rough grey bark has fissures, the stems and branches are finely hairy when young and become smooth with age. The leathery bright green leaves are arranged whorled, or alternately on branches, and are borne on 0.5–1.1 mm long petioles. They measure 3–9 cm (1.4–3.8 in) in length, and 0.7–1.2 cm (0.3–0.5 in) in width, and are elliptic in shape with entire (straight) recurved margins. They are initially hairy and become smooth with maturity, although their undersides remain covered with white hair. Individual flowers open from the base of the flower spike, the wave of anthesis moving up the inflorescence. Occasionally, flowers on exposed parts may open early. It takes around 9.5 days for all flowers to open, and rates are similar during the day and night. The inflorescences age to grey and the individual old flowers linger for some time before falling. Up to 100 small woody follicles may follow on old flower spikes. Measuring 1.1–1.5 cm wide, 3–4 mm wide, and jutting out 2–3 mm from the spike, they open after several years, releasing the seed. yet it did not result in formal publication of the species. The next known collection was in December 1801, during the visit of HMS Investigator to King George Sound. Little is known of the circumstances of this collection, other than what is written on the specimen label: "King Georges Sound Dec[embe]r 1801". The specimen is credited to Robert Brown, but gardener Peter Good and the botanical artist Ferdinand Bauer also contributed to Brown's specimen collection, often without attribution. A more precise date and location cannot be given, as neither Brown nor Good mentions the collection in his diary. Bauer did not publish an illustration of the species and his original field sketches are lost, but William Westall appears to have incorporated it into two of his field sketches, and certainly included it in the foreground of one of the oil paintings that he later worked up for the Admiralty. Brown formally described and named the species in his 1810 On the Proteaceae of Jussieu. He did not identify a type specimen, but the one specimen in his collection has since been formally declared the lectotype for the species. He also did not explicitly give an etymology for the specific epithet, but it is accepted that the name derives from the Latin verticillatus ("whorled"), in reference to the whorled leaf arrangement. No subspecies or varieties of Banksia verticillata have been identified and it has no taxonomic synonyms. In 1891, Otto Kuntze, in his Revisio Generum Plantarum, 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 verticillata. 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.

In Brown's arrangement of Banksia, B. verticillata was placed between B. compar (now B. integrifolia subsp. compar) and B. coccinea (scarlet banksia) in phyletic order. No infrageneric arrangement was provided other than the removal of one distinctive species into a subgenus of its own, because of its unusual domed flower head. As B. verticillata flowers occur in characteristic flower spikes, it was retained in Banksia verae, the "true banksias". A more detailed arrangement was published by Carl Meissner in 1856. Eubanksia was demoted to sectional rank, and divided it into four series. B. verticillata was placed in series Salicinae because its leaves are more or less linear, and have white undersides. Based as they were on leaf characters, Meissner's series were highly heterogeneous, This arrangement would stand for over a century. For many years there was confusion between B. verticillata and B. littoralis (swamp banksia). Until 1984, the latter was circumscribed as encompassing what is now Banksia seminuda (river banksia), which has whorled leaves like B. verticillata. Thus it was easy to perceive B. verticillata as falling within the range of variation of this broadly defined species. The confusion was largely cleared up once B. seminuda was recognised as a distinct taxon. Alex George published a new taxonomic arrangement of Banksia in his landmark 1981 monograph The genus Banksia L. f. (Proteaceae). Endlicher's Eubanksia became B. subg. Banksia, and was divided into three sections, one of which was Oncostylis. Oncostylis was further divided into four series, with B. verticillata placed in series Spicigerae because its inflorescences are cylindrical. This clade became the basis of Thiele and Ladiges' B. subser. Occidentales, which was defined as "characterised by opposite decussate seedling leaves and adult leaves in true whorls." (B. seminuda is omitted because it was not sampled in the study, not because it occurs elsewhere in the cladogram.)

Banksia verticillata is found in scattered populations in two disjunct segments: one clustered around Walpole, and the other around Albany and eastwards to Cheynes Beach. All but one are located within 2 km (1.5 mi) of the coast, the exception is less than 10 km (6 mi) inland. Plants grow on exposed coastal granite outcrops, often in cracks within boulders as well as shallow rocky soils. It is the only Banksia which grows exclusively in a granite soil. It grows in association with Taxandria marginata, Western Australian peppermint (Agonis flexuosa), Andersonia sprengelioides and species of Hakea in scrub and heath. Small mammals are not major pollinators, although bush rats (Rattus fuscipes) and house mice (Mus musculus) have been recorded. Honey bees (Apis mellifera) visit flower spikes but are not effective pollinators.

Banksia verticillata has been declared vulnerable under the federal Environment Protection and Biodiversity Conservation Act 1999, and Rare under Western Australia's Wildlife Conservation Act 1950. A 1995 census yielded an estimated total population size of 4500 plants. Seed has been collected from many populations, but germination rates after ten years of storage are much lower than in Banksia brownii. but must be carefully managed as studies have shown that foliar spraying of phosphite adversely affects root and shoot growth.

Banksia verticillata is seldom seen in cultivation. The natural growing conditions point to a sunny aspect and good drainage as being important in cultivation. It is good for coastal situations and erosion control. Very sensitive to dieback, B. verticillata (like most other western Australian banksias) perishes quickly in humid conditions or poor drainage. It has been grafted successfully onto Banksia integrifolia. Seeds do not require any treatment, and take 19 to 49 days to germinate.