About Banksia spinulosa Sm.
Banksia spinulosa Sm., commonly called hairpin banksia, usually grows as a multi-stemmed lignotuberous shrub 1–3 metres (3.3–9.8 ft) tall and 1–2 metres (3.3–6.6 ft) across. It can also grow as a single-stemmed plant without a lignotuber, reaching up to 5 metres (16 feet) in height. It has smooth grey or grey-brown bark marked with lenticels. Its leaves are long, narrow and roughly linear, measuring 3–10 cm (1.2–3.9 in) long and 1–8 mm wide. Leaf margins are either fully serrated (for the collina variety) or only serrated near the apex (for the spinulosa variety); margins may also be recurved, hiding serrations in some plants from the Carnarvon Gorge. Immature leaves, which may also appear after bushfire, are broader and fully serrated. The underside of leaves have fine white hairs for varieties spinulosa and collina, and pale brown hairs for varieties cunninghamii and neoanglica. Its distinctive inflorescences, also known as flower spikes, appear over a short period in autumn and early winter. Each spike can hold hundreds to thousands of individual flowers. Every individual flower has a tubular perianth made of four joined tepals, and one long wiry style. As is characteristic of the taxonomic section this species belongs to, styles are hooked rather than straight. The end of the style is initially trapped inside the upper perianth parts, but breaks free when the flower opens at anthesis. The spikes of Banksia spinulosa are cylindrical, around 6–7 centimetres (2.4–2.8 inches) wide and 6–15 centimetres (2.4–5.9 inches) tall, with a yellow to golden orange colour. Styles range in colour from yellow to pink, maroon, or black. In some locations such as Georges River National Park and Catherine Hill Bay, styles of different colours can occur within metres of each other, while other populations have uniformly black, red or gold styles. Though they do not grow at stem tips, the flower spikes are prominent, emerging partially from foliage and growing from two- to three-year-old stem nodes. The infructescence of hairpin banksia is a typical cone-like Banksia structure, holding up to 100 crowded embedded follicles that are 1–2.4 cm (0.4–0.9 in) in diameter. These follicles generally remain closed until opened by bushfire. The non-lignotuberous subspecies cunninghamii is killed by fire and regenerates from seed, while other varieties regenerate from buds around the base of the lignotuber. Old flower spikes fade to brown, then turn grey as they age. Old flower parts usually persist for a long time, giving the infructescence a hairy appearance. In Central and North Queensland, old cones of both var. spinulosa and var. collina are typically bare. This species occurs along Australia's east coast, from the Dandenong Ranges east of Melbourne, Victoria, northwards through New South Wales into Queensland. It is common north to Maryborough, with isolated disjunct populations occurring as far north as the Atherton Tableland near Cairns. It grows in a range of habitats: coastal heath for spinulosa and collina, elevated rocky slopes for neoanglica and spinulosa, and inland dry sclerophyll forest dominated by eucalypts, where it forms part of the understorey. Plants growing in exposed areas are typically much shorter than those growing in sheltered areas. It usually grows on sand, but can also be found in rocky clays or loams. Banksia spinulosa var. cunninghamii is found in three disjunct regions: the Dandenong Ranges east of Melbourne, East Gippsland between Lakes Entrance and Eden, and a band along the Great Dividing Range from Jervis Bay to Glen Davis in central New South Wales, with collections recorded further north along the range into southeast Queensland. It grows as an understorey plant in both dense and open forest. Like other banksias, Banksia spinulosa hosts a wide variety of pollinators and is an important source of nectar in autumn, when few other flowers are in bloom. It has been the focus of multiple pollination studies. A 1998 study conducted in Bungawalbin National Park in Northern New South Wales found that inflorescences of Banksia spinulosa var. collina are foraged by a range of small mammals, including the marsupial Antechinus flavipes (yellow-footed antechinus). These mammals carry pollen loads comparable to nectar-eating birds, making them effective pollinators. The same study also noted that, unlike other studied banksias, B. spinulosa var. collina is predominantly visited by native bees rather than the introduced Apis mellifera (European honeybee). Many different bird species have been observed visiting this species. A 1982 study in New England National Park in northeastern New South Wales found that a large influx of Acanthorhynchus tenuirostris (eastern spinebill) coincided with the start of local B. spinulosa flowering. On the Blackdown Tableland, Lichenostomus leucotis (white-eared honeyeater), Lichenostomus melanops (yellow-tufted honeyeater), and pygmy possums visit B. spinulosa. Brown antechinus, sugar glider, and bush rat are also known to visit flowers. Additional species recorded visiting this species in The Banksia Atlas survey include Phylidonyris nigra (white-cheeked honeyeater), Phylidonyris pyrrhoptera (crescent honeyeater), Meliphaga lewinii (Lewin's honeyeater), Lichmera indistincta (brown honeyeater), Manorina melanocephala (noisy miner), Philemon corniculatus (noisy friarbird), Anthochaera carunculata (red wattlebird) and Eopsaltria australis (eastern yellow robin). Like most other Proteaceae, B. spinulosa produces proteoid roots: roots with dense clusters of short lateral rootlets that form a mat in the soil just below leaf litter. These roots improve nutrient solubilisation, allowing the plant to take up nutrients in low-nutrient soils such as the phosphorus-deficient native soils of Australia. Banksia spinulosa is not considered threatened. It is resistant to Phytophthora cinnamomi dieback, a major threat to many other Banksia species, and its wide distribution protects it from habitat loss caused by land clearing. Because of this, it is not listed on Australia's list of threatened flora under the Environment Protection and Biodiversity Conservation Act 1999. In New South Wales, it is listed in Part 1 Group 1 of Schedule 13 of the National Parks and Wildlife Act 1974; this classification means that as a common and secure species, it is exempt from any licensing or tagging requirements under the 2002–2005 management plan that regulates and minimises use of protected and threatened plants in the cut-flower industry. Banksia spinulosa var. spinulosa was introduced to cultivation in the United Kingdom in 1788 by Joseph Banks, who supplied seed to institutions including Kew Gardens, Cambridge Botanic Gardens and Woburn Abbey. Var. collina was introduced in 1800, followed by var. cunninghamii in 1822. It has proven to be a highly ornamental plant that attracts birds in cultivation. Forms from southern and montane provenances are frost hardy. In general, all varieties prefer sandy, well-drained soils grown in full sun, though some local forms originating from Wianamatta shales can tolerate heavier soils. It is resistant to dieback, like most eastern banksias. Because it naturally grows on acid soils, Banksia spinulosa is particularly sensitive to iron deficiency. This condition, called chlorosis, causes yellowing of new leaves while leaf veins remain green, and develops when the plant is grown in higher pH soils. It can also occur where soil contains cement residue from landfill or building foundations, and can be treated with iron chelate or iron sulfate. Regular pruning is recommended to keep an attractive growth habit and prevent the plant from becoming leggy. Since most cultivated forms of this species have a lignotuber, dormant buds exist under the bark that respond to pruning or fire, and hard pruning almost to ground level is possible, as the plant can readily resprout from old wood. This does not apply to var. cunninghamii, which should not be pruned below the foliage. Flowering can take up to eight years from germination; purchasing an advanced plant, or growing a cutting-grown plant, can speed up flowering. Banksia spinulosa can be easily propagated from seed, and is one of the relatively easier banksias to propagate from cuttings. Named cultivars must be propagated from cuttings to ensure plants retain the same characteristics as the original parent plant. Both B. s. var. collina and var. spinulosa are commonly sold in nurseries. Since the varieties can hybridise, it is environmentally preferable to source a local provenance form from a local community nursery, Bushcare group, or Australian Plants Society group if plants are to be planted in gardens near bushland with native populations. Several dwarf forms are available for urban gardeners: 'Stumpy Gold' is a form of var. collina originally from the Central Coast of New South Wales, while 'Birthday Candles', 'Coastal Cushion' and 'Golden Cascade' are forms of var. spinulosa from the South Coast of New South Wales.
