Banksia serrata (Banksia serrata)

Description

Banksia serrata usually grows as a gnarled and misshapen tree up to 16 m (50 ft) tall, although in some coastal habitats it grows as a shrub of 1–3 m (3–10 ft), and on exposed coastal cliffs it has even been recorded as a prostrate shrub. As a tree it usually has a single, stout trunk with warty, knobbly grey bark up to 3 cm (1.2 in) thick. Trunks are often black from past bushfires, and ooze a red sap when injured. New growth appears in spring, summer and autumn. New branchlets are hairy, remaining so for two to three years. Leaves are usually crowded together at the upper end of branches, giving the canopy a thin, sparse appearance. The leaves themselves are dark glossy green above and light green below, 7 to 20 centimetres (2.8 to 7.9 in) (rarely up to 26 centimetres (10 in)) long by 2 to 4 cm (0.8 to 1.6 in) (rarely up to 4.5 cm (1.8 in)) wide, and oblong to obovate (egg-shaped) in shape. The leaf margins are serrated, except near the base, with lobes between 1 and 3 millimetres (0.04 and 0.12 in) deep. Cylindrical flower spikes, or inflorescences, grow from the ends of 1–2 year-old branchlets and have leaves at their base. The spikes are generally 9 to 12 centimetres (4 to 5 in) wide with hundreds of individual flowers arising from an upright woody axis. The woody axis is 7 to 15 centimetres (3 to 6 in) high and 0.9 to 1 centimetre (0.35 to 0.39 in) wide. The flowers are cream-grey in colour with cream styles. Old flower spikes develop into "cones" that consist of up to thirty follicles that develop from the flowers that were pollinated. Old withered flower parts remain on the cones, giving them a hairy appearance. Each follicle is oval in shape, wrinkled in texture, covered with fine hair and 2.5–3.5 cm (1.0–1.4 in) long, 2.0–2.5 cm (0.8–1.0 in) thick, and 1.5–2.2 cm (0.6–0.9 in) wide. The obovate seed is 3–3.4 cm (1.2–1.3 in) long, fairly flattened, has a papery wing and weighs around 77.5 mg (0.00273 oz). The seed is composed of the obovate seed body (containing the embryonic plant) and measures 1.0–1.2 cm (0.39–0.47 in) long by 0.9–1.1 cm (0.35–0.43 in) wide. One side, termed the outer surface, is pitted and dark brown and the other is brown-black and warty, sparkling slightly. The seeds are separated in the follicle by a sturdy dark brown seed separator, which is about the same shape as the seeds, with a depression where the seed body sits adjacent to it. The first pair of leaves (called cotyledons) produced by seedlings are obovate, dull green and measure 1–1.4 cm (0.39–0.55 in) long by 1–1.5 cm (0.39–0.59 in) wide. The auricle at the base of the cotyledon leaf is pointed and measures 0.2 cm (0.079 in) long. The hypocotyl is thick, hairy and red. The cotyledons are linear to lance-shaped with the narrow end towards the base, 3.5–10 cm (1.4–3.9 in) long with serrated margins and a v-shaped sinus at the tip. Banksia serrata closely resembles B. aemula, but the latter can be distinguished by an orange-brown, rather than greyish, trunk, and adult leaves narrower than 2 cm (0.79 in) in diameter. The inflorescences of B. serrata are generally a duller grey-yellow in colour, have longer (2–3 mm), more fusiform or cylindrical pollen presenters on the tips of unopened flowers and the follicles are smaller.