BURSARIA- by Phil Watson

A MATTER OF BIRDS, BARBS AND BUTTERFLIES
 
 

Pittosporaceae

Bursaria spinosa
Walkers, wandering through their favourite woodland patches throughout the year, mostly pass Bursaria spinosa or “Sweet Bursaria” without giving it a second glance. However, around Christmas time, when the woodland's spring flower colour parade is but a withering memory, it tends to attract their attention. This is a response to its sweet “Pittosporum-like” scent and the attractive panicles of small star-like white flowers blanketing the bushes.

The botanical inquisitiveness of the walkers is subsequently prompted enough to engage in a closer inspection. This often leads to the muttering of the name 'Christmas Bush' amongst the group. Commonly at this point, little further interest is shown, consequently the profusion of insect and bird life humming around these plants remains undisturbed, as the walkers continue on their merry way, decidedly disinterested in any further examples of this 'take-it-for-granted' shrub. The following summary explores some of the reasons why this shrub should be considered anything but uninteresting!

Common Names Galore   Its abundance across southern Australia has resulted in a variety of common names. These include “Christmas Bush” and “Sweet Bursaria” that were discussed earlier, However the names “Blackthorn” and  “Prickly Box” were initially used by the early graziers, who were frustrated by its persistence in snagging the wool of passing sheep or bloodying browsing cattle with its sharp spines. The name “Native Box” relates to colonial pastoralists using it as a hedging plant, often as a substitute to the more sinister invasive weed species Lycium ferosissima (“Boxthorn”).  “Boxwood”is another common name that has been applied to the small tree specimens of this plant that  not only have an attractive box-like bark, but also provide a source of quality, attractively figured, craft wood.

Why the Bursaria spinosa?   "Bursaria" derives from the Greek word bursa, meaning a sac, pouch or purse-like structure. The applicability of the word to this plant is obvious, given the many purse-like seed capsules that are prominently displayed from late summer onwards. “Spinosa” refers to the spiny/thorny nature of the most common subspecies, namely Bursaria spinosa var. spinosa, which is typically located in harsher conditions. Bursaria spinosa var. macrophylla is a broader leafed, non-spiny subspecies growing in moister, less demanding woodland environments.

Horticultural Attributes.   English and Californian horticulturalists have landscaped with Sweet Bursaria for more than a hundred years, describing it as “charming” and “delightful”. This is in recognition of its pleasant summer floral display, coupled with its handsome tessellated box-like bark.
These attributes make it a useful specimen plant or, alternatively, a hedging plant. A row of closely planted Bursaria seedlings will produce an impenetrable formal hedge, if regularly clipped. A natural, taller and more open hedge results if they are allowed to grow unchecked. This informal hedge provides excellent bird nesting sites and spider webbing locations.

Indigenous plantings of Bursaria can perform “anti-personnel” functions. Their spiny nature directs pedestrian movement in the landscape, assists in minimising the vandalism of new plantings and protects the native feathered and furry creatures from marauding domestic pets.

Following weeding activities, targeting the vicious “boxthorn” weeds that are often located in open paddocks and grassy communities, Bursaria has proven to be the ideal replacement plant. Its tight, spiny form, similar to boxthorn, provides a reasonable habitat substitute for the many creatures that would have adapted to the earlier protection offered by the boxthorn bushes.

Ecological Considerations.   Sheep and cattle browsing in degraded woodland communities (bush runs), cause the demise of many native shrubs, herbs, grasses and groundcovers. This is a consequence of the persistent grazing of the foliage in the native understorey and any young succulent seedlings that may germinate. Depending on the stocking rates and how long the grazing continues unabated, the ecological values of the woodland community may diminish rapidly. At a stage just prior to when natural regeneration loses its ability to heal the land, the degradation signs are typically browsed Bursaria shrubs standing as solitary sentinels amongst a plethora of introduced pasture weeds and erosion scars.

However, all is not lost! With a little education and attitudinal change by the land manager, accompanied by an effective stock control fence installed after the de-stocking of the bush run, natural regeneration can begin to restore the original woodland community. Important in this natural regeneration process is the role of the tolerant Bursaria remnants. These not only provide critical habitat for the recolonisation by insects and birds but also provide a protective framework for young native seedlings to germinate and grow from the native seed stored in the soil. Each Bursaria bush offers a nectar and larval food source for birds, beetles, butterflies, moths, wasps, bees, ants, etc. This in turn allows pollination, seed dispersal and nutrient cycling processes to be initiated. These are the building blocks for successful natural regeneration of degraded woodland communities.

Hill topping Sites.   Hill topping sites have recently been recognised for their role as foci for mating of
butterflies, providing sites proud of the lower sea of exotic pastures for the mating. The mating process brings together a mixture of genetic material from sparse and frequently isolated butterfly populations.  These degraded rocky outcrop remnants, often consist of only a framework of hardy Acacia spp. and Bursaria trees and shrubs along with a few species of native grasses, sedges and groundcovers. However, degraded as they are, they still provide a stable set of physical and botanical features recognisable by the male butterflies, which will comfortably use these sites to attract passing females. The stability is essential, as the male butterflies will otherwise abandon the sites if rapid changes, such as further clearing or extensive revegetation activities, occur. Local butterfly extinctions and the subsequent loss of pollinators for local provenance plants are the obvious negative outcomes.

The Bright Copper Butterfly   This butterfly relies on Bursaria for its larval food. and is often seen in the upper suburbs of Hobart following the pupation of its caterpillars. It has a symbiotic relationship with black ants that attend its caterpillars protecting them from predators, in exchange for their honey-like fluid secretions.
Butterfly links:
Bright Copper butterfly
Common Brown butterfly
Shouldered Brown butterfly

Spider Web Sites   Bursaria bushes provide an intricate architecture of thorns and twiggy foliage much sought after by numerous species of spiders for constructing their webs. When the bushes are flowering, their sweet nectar attracts a myriad of insects, only to be entrapped in these three-dimensional spider snares. The spider webs too have an important role in attracting a diversity of indigenous birds - Grey Fantails, Crescent, Black Headed and New Holland Honeyeaters, Tasmanian and Brown Thornbills and all our Robins etc. depend upon the collection of spider web remnants to knit their nests together for successful nest building to be completed. Bursaria not only offers a safe location for nest building, but also supplies a source of essential ingredients.

"Aesculin" An extract from the leaves.  The glycoside named Aesculin, found only in sufficiently high concentrations within the leaves of Bursaria, proved very important to the World War 2 military forces. Prior to that, Aesculin was only extracted in very low concentrations from the bark of the English "Horse Chestnut" trees (Aesculus hippocastaneum ) following the felling of the tree. This destructive process was curtailed when it was discovered that this active agent could be extracted from the dried Bursaria leaves, after hammer milling and solvent extraction.

Aesculin provided the active ingredient for a sun screening lotion for the fully exposed allied turret gunners during their numerous bombing raids over Europe. It also proved a valuable bacteriological reagent in the testing for tropical diseases for Australian Forces in the tropics and again was used for effective treatment of blood vessel disorders of Australian servicemen, including its use as an agent to manage haemorrhoids.

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