Banksia aemula

Shrub of the family Proteaceae found on the Australian east coast

Banksia aemula, commonly known as the wallum banksia, is a shrub of the family Proteaceae. Found from Bundaberg south to Sydney on the Australian east coast, it is encountered as a shrub or a tree to in coastal heath on deep sandy soil, known as Wallum. It has wrinkled orange bark and shiny green serrated leaves, with green yellow flower spikes, known as inflorescences, appearing in autumn. The flower spikes turn grey as they age and large grey follicles appear. Banksia aemula resprouts from its woody base, known as a lignotuber, after bushfires. First described by the botanist Robert Brown in the early 19th century, it derives its specific name "similar" from its resemblance to the closely related Banksia serrata. No varieties are recognised. It was known for many years in New South Wales as Banksia serratifolia, contrasting with the use of B. aemula elsewhere. However, the former name, originally coined by Richard Anthony Salisbury, proved invalid, and Banksia aemula has been universally adopted as the correct scientific name since 1981. A wide array of mammals, birds, and invertebrates visit the inflorescences and are instrumental in pollination; honeyeaters are particularly prominent visitors. Grown as a garden plant, it is less commonly seen in horticulture than its close relative B. serrata.

Banksia aemula is generally a gnarled shrub or small tree to , although usually smaller. The shiny green leaves are obovate to oblong in shape and measure in length, and in width. The leaf ends are truncate and the margins flat and serrated. Flowering is in autumn, from March to June; the green yellow flower spikes, known as inflorescences, are terminal, found on the ends of branches and emerging from the foliage. Measuring in height and in width, they are various shades of pale and greenish yellow. in a process known as sequential anthesis. Each flower produces nectar for around seven days after opening. The flower spikes turn grey as they age and up to 25 finely furred grey follicles appear, which can be very large, measuring long, high, and wide. They split open either after bushfire or spontaneously, and release oval seeds in length, composed of a wedge shaped body long and wide, and curved wing wide. Banksia aemula resprouts from its woody lignotuber after fire. Finally, the follicles are smaller.

Banksia aemula is found along the east coast of Australia from around north of Bundaberg in central Queensland down to Sydney. It is also found on Fraser, Moreton and North Stradbroke Islands. Almost all populations are within a few kilometres of the coast, except for one at Agnes Banks in western Sydney, and two just north and south of Grafton at Coaldale and Glenreagh, and a last around southwest of Bundaberg. In Cooloola National Park, it is an occasional emergent plant (along with Melaleuca quinquenervia and Eucalyptus umbra) in closed graminoid heathland, a community of shrubs high containing Xanthorrhoea fulva, Empodisma minus, Petrophile shirleyae, and Hakea and Leptospermum species. On the New South Wales Central Coast, it generally grows as a high shrub and is a canopy component of Banksia aemula open heathland, located on coastal headlands on highly leached Pleistocene white sands overlying Triassic and Permian strata. Areas include Wybung Head in Munmorah State Conservation Area, and near Myall Lakes. Other plants it grows in association with include Ricinocarpos pinifolius, Brachyloma daphnoides, Dillwynia glaberrima, D. retorta, Allocasuarina distyla, Bossiaea ensata, Aotus ericoides, Phyllota phylicoides, and Empodisma minus. Sandmining has eradicated much of the community around Redhead. In less leached yellower sands, the community (and B. aemula) is replaced by a taller heath containing B. serrata and B. oblongifolia. At the southern end of its range, B. aemula is a component of the Eastern Suburbs Banksia Scrub, designated an endangered ecological community. This community is found on younger, windblown sands than the heathlands to the north. The Agnes Banks Woodland in western Sydney has been recognised by the New South Wales Government as an Endangered Ecological Community. Here Banksia aemula is an understory plant in low open woodland, with scribbly gum (Eucalyptus sclerophylla), narrow leaved apple (Angophora bakeri) and B. serrata as canopy trees, and B. oblongifolia, Conospermum taxifolium, Ricinocarpus pinifolius, Dillwynia sericea and nodding geebung (Persoonia nutans) as other understory species. On North Stradbroke Island, B. aemula is one of three canopy tree species of Eucalyptus signata dominated forest high, the third species being E. umbra. This forest is found on a ridge above sea level formed from an ancient sand dune. Here bracken (Pteridium esculentum) dominates the understory. Other tall shrubs associated include Persoonia cornifolia and Acacia concurrens.

Most Proteaceae and all Banksia species, including B. aemula, have proteoid roots, roots with dense clusters of short lateral rootlets that form a mat in the soil just below the leaf litter. These roots are particularly efficient at absorbing nutrients from nutrient poor soils, such as the phosphorus deficient native soils of Australia. A study of six wallum species, including B. aemula, found they have adapted to very low levels of phosphorus and are highly sensitive to increased levels of the element, leading to phosphorus toxicity. Some evidence suggests they are efficient at using potassium, and sensitive to calcium toxicity as well. A field study on North Stradbroke Island noted increased root growth in autumn (around April), but that overall root growth was more constant than other species looked at, possibly because its deeper roots had more regular access to groundwater. A 1998 study in Bundjalung National Park in northern New South Wales found that B. aemula inflorescences are foraged by a variety of small mammals, including marsupials such as yellow footed antechinus (Antechinus flavipes), and rodents such as pale field rat (Rattus tunneyi), Australian swamp rat (R. lutreolus) and grassland melomys (Melomys burtoni) and even the house mouse (Mus musculus). These animals carry pollen loads comparable to those of nectarivorous birds, making them effective pollinators. Grey headed flying foxes (Pteropus poliocephalus) were also observed visiting B. aemula and their heads and bellies were noted to contact stigmas while feeding. Bird species that have been observed feeding at the flowers of B. aemula include rainbow lorikeet and scarlet and Lewin's honeyeaters. Intervals of 10–15 years are recommended for the Eastern Suburbs Banksia Scrub, as longer leads to overgrowth by Leptospermum laevigatum. Experimenting with seed germination and early growth of B. aemula showed that phosphorus was toxic to seedlings, inhibiting growth at double normal soil concentrations and causing seedling death at quadruple normal soil concentrations. The addition of potassium or magnesium ameliorated these effects a little although potassium in high concentrations impacted on growth as well. Overall, seedlings grow slowly over the first 21 weeks of life compared with other plant species, the reasons for which are unclear, although it may be that it offers an increased chance of survival in a nutrient or water poor environment. Seed was killed by exposure to 150°C, but survived seven minute exposure to 100°C. A study of coastal heaths on Pleistocene sand dunes around the Myall Lakes found B. aemula grew on ridges (dry heath) and B. oblongifolia on slopes (wet heath), and the two species did not overlap. Manipulation of seedlings in the same study area showed that B. aemula grows longer roots seeking water and that seedlings do grow in wet heath, but it is as yet unclear why the species does not grow in wet heath as well as dry heath. Unlike similar situations with banksia species in Western Australia, the two species did not appear to impact negatively on each other. A field study on seedling recruitment conducted at Broadwater National Park and Dirrawong Reserve on the New South Wales North Coast showed that generally Banksia aemula produced seedlings in low numbers but the attrition rate was low, and that seedlings had a greater survival rate on dry rather than wet heaths. Field work including the experimental planting out of seedlings at Crowdy Bay National Park showed that Banksia aemula seedling roots reach the water table within six months of germination, and that they can germinate in the presence or absence of recent bushfire. The reasons for bradyspory (that is fewer seeds with greater percentage of survival) is unclear, but may be a defence against seed eating animals. Similarly in field work on North Stradbroke Island, B. aemula was noted to shed its winged seeds over time between (as well as after) fire, and germinate and grow readily with little predation by herbivores. and Noosia banksiae, representing a new genus, in 2011. Another new fungal species, Saitozyma wallum, was described in 2019 from a B. aemula leaf on the Sunshine Coast, Queensland.

In 1788, Banksia aemula was one of the first banksias to be cultivated in England, It is also a bird and insect attracting plant. Trials in Western Australia and Hawaii have shown B. aemula to be resistant to Phytophthora cinnamomi dieback. It requires a well drained slightly acid (pH 5.5–6.5) soil, the plant takes four to six years to flower from seed. It has also been used as a rootstock for grafting Banksia speciosa, and has potential in bonsai. The red textured timber has been used in cabinet making.

Although Banksia attenuata was the common banksia in Australian children's author May Gibbs' own childhood in Western Australia, the old flower spikes of Banksia aemula with their large follicles are thought to have been the inspiration for the villains of her Snugglepot and Cuddlepie books, the "Big Bad Banksia Men".