Banksia verticillata
| Granite banksia | |
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| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| Order: | Proteales |
| Family: | Proteaceae |
| Genus: | Banksia |
| Species: | B. verticillata |
| Binomial name | |
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Banksia verticillata R.Br. |
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| Distribution of B. verticillata in Western Australia. | |
Banksia verticillata, commonly known as granite banksia or Albany banksia, is a species of shrub or (rarely) tree of the genus Banksia in the family Proteaceae. It is native to the southwest of Western Australia and can reach up to 3 m (10 ft) in height. It can grow taller to 5 m (16 ft) in sheltered areas, and much smaller in more exposed areas. This species has elliptic green leaves and large, bright golden yellow inflorescences or flower spikes, appearing in summer and autumn. The New Holland honeyeater (Phylidonyris novaehollandiae) is the most prominent pollinator, although several other species of honeyeater, as well as bees, visit the flower spikes.
A declared vulnerable species, it occurs in two disjunct populations on granite outcrops along the south coast of Western Australia, with the main population near Albany and a smaller population near Walpole, and is threatened by dieback (Phytophthora cinnamomi) and aerial canker (Zythiostroma). B. verticillata is killed by bushfire and new plants regenerate from seed afterwards. Populations take over a decade to produce seed and fire intervals of greater than twenty years are needed to allow the canopy seed bank to accumulate.
Banksia verticillata grows as a spreading, bushy shrub with many branches up to 3 m (10 ft) high, but can reach 5 m (16 ft) high in sheltered locations. 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) margins. They are initially hairy and become smooth with maturity, although their undersides remain covered with white hair. The golden-yellow inflorescences appear in summer and autumn (January to April) and are 8–20 cm (3–8 in) high and 6.5 cm (2.6 in) wide. The smooth pistils are 3–3.5 cm long and hooked at the end. 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. Follicles more commonly appear in the middle third of the spike. The reasons for this are unknown, although timing of visits by pollinators or some anatomical factor may be relevant.
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