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Bursaria spinosa is a small tree or shrub in the family Pittosporaceae. The species occurs mainly in the eastern and southern half of Australia and not in Western Australia or the Northern Territory. Reaching 10 m (35 ft) high, it bears fragrant white flowers at any time of year but particularly in summer. A common understorey shrub of eucalyptus woodland, it colonises disturbed areas and fallow farmland. It is an important food plant for several species of butterflies and moths, particularly those of the genus Paralucia, and native bees.
Bursaria spinosa is highly variable in appearance and habit, as are other species within the genus, and there have been several attempts at classification since their discovery. For example, in 1893, Jules Alexandre Daveau, in Désiré Georges Jean Marie Bois's Dictionnaire d'Horticulture, described varieties inermis (meaning 'without spines') and macrophylla ('large leaves'), but var. macrophylla was a nomen illegitimum because it had already been used by William Jackson Hooker in 1834.
A 1999 revision of the genus recognised only two subspecies and the names are accepted by the Australian Plant Census:
Subspecies lasiophylla had been known as Bursaria lasiophylla, first formally described in 1978 by Eleanor Marion Bennett, but reduced to a subspecies by Lindy Cayzer, Michael Crisp and Ian Telford in 1999.
In New South Wales, B. spinosa grows in dry to wet forest in all but the most arid parts of the state, and is sometimes a weed on cleared land. In the Sydney region, it grows on clay- and shale-based soils, as an understory plant in association with grey box ( Eucalyptus moluccana) and forest red gum ( E. tereticornis) as well as the grass Themeda australis. It can form thickets on ungrazed farmland. In Victoria, the species is widespread and common throughout the state, except for the far northwest, in heavier soils and in alpine areas, in South Australia it is widespread in the south-east of the state, and in Tasmania it mainly occurs in dry areas.
Subspecies lasiophylla has a more restricted distribution, and in New South Wales is found on the central and south coasts and central and southern tablelands, growing in woodland on heavier clay soils than subsp. spinosa. In Victoria, this subspecies mainly grows in dry, rocky places in forest and shrubland in eastern and central-western areas of that state.
A wide variety of insects visit the flowers of Bursaria spinosa, the most important pollinators of which appear to be beetles of several families. Common visitors recorded from field work around Armidale were Buprestidae species, such as Curis splendens and Stigmodera inflata; Cerambycidae including Amphirhoe sloanei and Tropocalymma dimidiatum; scarabaeidae; and mordellidae. Beetles and Scoliidae all carried significant amounts of pollen. Other visitors, such as flies and butterflies, carried much lower amounts. The larvae of the jewel beetle species Astraeus crassus live in tunnels in dead and dying branches. Caterpillars which feed on Bursaria spinosa include Proselena annosana, two-ribbed arctiid ( Palaeosia bicosta) and bark looper moth ( Ectropis subtinctaria), while those of the clouded footman ( Anestia ombrophanes) graze on algae and lichens which grow on the branches.
The bright copper ( Paralucia aurifera) and ant species Anonychomyrma nitidiceps form a complex symbiotic relationship on Bursaria spinosa. Butterflies lay their eggs on the underside of the leaves, and the caterpillars feed on the leaves before pupating in the soil at the foot of the plant. The ants excavate chambers in the soil where the caterpillars sleep and later pupate, and accompany the caterpillars when the latter are feeding. They are thought to feed on the caterpillars' secretions. Caterpillars of the fiery copper ( Paralucia pyrodiscus) are likewise accompanied by ants of the genus Notoncus, and the third species, the endangered Bathurst copper ( Paralucia spinifera), also breeds and feeds exclusively on the subspecies lasiophylla in Central New South Wales.
Cattle and rabbits graze on young plants.
Ecology
Living for 25 to 60 years, Bursaria spinosa can resprout from its woody base after bushfire. Highly rhizome, plants of a stand are often genetically a single plant. Despite being genetically identical, different plants and even single shoots can be very distinct in appearance (for instance, spineless shoots previously regarded as a subspecies "inermis"). Its seed is wind-dispersed and it is a colonising plant.
Uses
The drug aesculin, used in medical research and in the 1940s, as an ingredient in sunscreen, is harvested from the plant in the Sydney region. Although its thorns make it unpopular in cultivation, it can be useful as a deterrent barrier. It can be grown from fresh seed or from cuttings and is hardy in most situations. Bursaria spinosa provides nectar for butterflies and a haven for small birds.
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