Banksia marginata
FAMILY: Proteaceae
BOTANICAL NAME: Banksia marginata
COMMON NAME: silver banksia
CONSERVATION SIGNIFICANCE:
None recorded
Richard Barnes
Description
Silver banksia is a species whose form can vary considerably. It can grow into a small
shrub of 0.5 m high or into a tree up to 12 m high. Individuals with weeping foliage
have even been seen. Variations also occur in leaf size and shape and other more
subtle physical features, such as the hairiness of the stem and leaf surfaces. Even
within one area there can be plants with different leaf types and growth habits.
Generally the leaves are alternate and scattered along the branches, and are attached
by a 2.5 mm long leaf stem. The leaf shape varies from linear to oblong to narrowly
wedge- or lance-shaped, with margins that are entire or sometimes serrated, more-orless flat or curled back or forward. The leaf tip can be blunt or squared or have a
distinct margin or a sharp point. The leaves range in size from 1–8 cm long and 3–15
mm wide. The upper surface of the leaf is dark green, and the lower surface white and
hairy. The branchlets are covered with spreading and/or short, curled hairs.
The numerous yellow or golden green flowers occur on a compact candle-shaped
spike that is 3–13 cm long and 4–6 cm wide. The individual flowers on the spike are
14–18 mm long, with softly hairy petals that form a tube. The long style protrudes
from the flower tube, where it becomes straight and spreading or curves backwards
where it emerges from the flower tube. Each flower on the spike forms a persistent
woody follicle that opens via two woody valves and contains 2 wedge-shaped winged
seeds, 5–8 mm long. There are approximately 150 follicles on a spike, each 7–17 mm
in length. The immature follicles are hairy, becoming hairless as they ripen, and
usually open when mature.
Flora of Tasmania
Banksia marginata
Some individuals form a lignotuber at the stem base, a woody swelling with dormant
buds that can regenerate after fire. On taller trees the normally thin, brown bark can
become thick and tessellated.
Silver banksia can be distinguished by the compact candle-shaped spikes of yellow or
gold-green flowers and the persistent woody cones.
Confusing species
None in Tasmania.
Distribution and Habitat
Distribution of Banksia marginata in Tasmania 2004 data.
Silver banksia occurs in South Australia, Victoria, New South Wales, the Australian
Capital Territory and Tasmania. It is locally common and widespread throughout
Tasmania, growing from sea level to over 1000 m (e.g. 1200 m at Mt Field National
Park). It occupies very variable habitats including wet sclerophyll forest, subalpine
woodland, sedgeland/heathland, sclerophyll shrubbery, buttongrass moorland, coastal
vegetation, heath, dry eucalypt forest and woodland. It occurs throughout many
cleared agricultural areas and often remains as remnant roadside vegetation and
isolated trees in paddocks. As a tree, it is relatively common on sheltered coastal sites
and dunes and in the grassy woodlands of the Midlands.
Ecology
Silver banksia is a very hardy, long-lived species that can tolerate a broad range of
environmental conditions. It is salt-tolerant, frost and drought-resistant and can
survive exposed windy sites. It can tolerate full sun or part shade and grow in a range
of soil types including sandy soils, loam and clay. Although it prefers soils that are
well-drained, it can tolerate moist and even waterlogged sites.
Flora of Tasmania
Banksia marginata
Banksia marginata (like all banksias) is able to survive in very nutrient-poor soils
because it possesses clusters of roots (proteoid roots) that exude substances called
carboxylates in and around the root zone. These substances make nutrients,
particularly phosphorus, more available to the banksia plant.
Banksia marginata, like many other banksia species, has a distinctive annual
branching pattern, with small, circular swellings formed at the junction of each annual
growth increment. It is possible to estimate the age of individuals by counting the
swellings, or nodes, each representing one year of growth. Banksia marginata,
survives up to 150 years.
Flowers can occur on the trees for most of the year, but are most profuse from
September through until April. The flowers are mainly bird-pollinated but pollination
by insects and sugar gliders has also been recorded. The woody capsules persist yearround on the plant at various stages of maturity. The seed ripens between February
and April. Ripeness is indicated when the follicles are dark brown and woody (not
soft and green/light tan when scratched).
Silver banksia, like many Australian natives, is phosphorus-intolerant and susceptible
to the root rot fungus, Phytophthora cinnamomi.
Banksia marginata is very tolerant of disturbance and very successful at regenerating
after disturbance. It is unpalatable to wildlife, which allows for higher seedling
survival rates. Fire plays an important part in its ecology, stimulating both
reproductive and vegetative regeneration, with a distinct burst of regeneration
following a fire. Fire releases the stores of seeds held in the persistent woody capsules
and creates a suitable environment for the seedlings to establish. The response of
individual banksias to fires varies, depending on their location and their genetic stock.
Some plants regenerate vegetatively, either from lignotubers or by re-sprouting from
epicormic buds (dormant buds under the bark). Suckering of plants has also been
recorded. On the other hand, some plants may be killed by fire and are thus dependent
on seed germination for regrowth. In general, there needs to be a fire-free period of at
least 8 years to allow plants to replenish the seed stored in the canopy, while at least a
10–20 year fire-free period is required to allow a substantial seed bank to accumulate.
Potential for Cultivation
This species has very high potential for cultivation as it is tolerant to such a wide
range of conditions. Silver banksia is amenable to pruning and is used regularly in
mixes for regeneration sites. It is a good species to use in wind breaks and shelter
belts and is particularly suitable for coastal areas.
Seed is easy to collect and grow and germinates within 4–8 weeks. Once seed is
collected, its viability declines rapidly unless the seed is stored properly. The seed is
likely to be orthodox (will survive dehydration) and would be easily kept viable for
longer periods if air-dried and stored at low temperatures. The seed requires low light
levels for successful germination. Some seed may need stratifying, depending on
where it was collected, and smoke treatment may be beneficial. This species can also
be propagated from cuttings taken from plants between the months of August and
October. Firm young growth must be used.
Flora of Tasmania
Banksia marginata
Information Sources
Australian Government (1988) The Banksia Atlas. Australian Flora and Fauna Series
No. 8. Australian Government Publishing Service, Canberra.
Curtis, W.M. (1967) The Student’s Flora of Tasmania. Part 3. St. David’s Park
Publishing, Hobart.
Corrick, M.G. & Fuhrer, B.A. (1999) Wildflowers of Victoria and Adjoining Areas.
Bloomings Books, Hawthorn, Victoria.
Jenkins, M.E., Morrison, D.A. & Auld, T.D. (2005) Use of growth characteristics for
predicting plant age of three obligate-seeder Proteaceae species. Australian Journal of
Botany. 53, 101–108.
Cameron, M. (ed.) (1981) Guide to Flowers and Plants of Tasmania. Launceston
Field Naturalists Club and Reed Books, Sydney, NSW.
Morley, B.D. & Toelken, H.R. (eds) (1983) Flowering Plants of Australia. Rigby,
Adelaide.
Ralph, M. (1994) Seed Collection of Australian Native Plants. (2nd ed). Imprenta,
Melbourne.
Ralph, M. (1997) Growing Australian Native Plants from Seed. Murray
Ralph/Bushland Horticulture, Fitzroy, Victoria.
Veneklaas, E.J., Lambers, H. & Cawthray, G. (2005) Root Exudates of Banksia
Species from Different Habitats – a Genus-wide Comparison. Report to the Australian
Flora Foundation.
Wills, T.J. (2003) Using Banksia (Proteaceae) node counts to estimate time since fire.
Australian Journal of Botany. 51, 239–242.
Understorey Network. Tasmanian Native Species Database. www.understoreynetwork.org.au
Walsh, N.G. & Entwisle, T.J. (1996) Flora of Victoria. Vol. 3. Inkata Press,
Melbourne.
Flora of Tasmania