Dodoneae filiformis (Tas endemic)
BREWS FROM THE HOP BUSHES
by Phil Watson
Hop Bushes or more endearingly called 'Dods' (Dodonaea viscosa spp.), provide an interesting brew of enthralling plant characteristics, uses and interrelationships. Their robustness enables them to flourish across a diverse range of open vegetation communities spanning areas of continental Africa, America, Australia and India. With its natural habitat spreading from exposed coastal fore dunes and cliffs to barren rocky ridges and grassy woodland communities, it has earned a reputation as a hardy water miser. Combined with its plant uses and attractive, vividly coloured 3 to 4 winged fruits,
glossy leaves and natural hedging ability, it deserves a recent increase in popularity as a desirable landscape and revegetation plant.
Subspecies of Dodonaea viscosa have distinctive characteristics
Dodonaea viscosa has a series of subspecies occurring in open woodlands in SE Australia. Their plant size, distinctive leaf shape and habitat range helps to distinguish between them. Key examples include Dodonaea viscosa ssp viscosa (large, nearly stalkless, elliptical leaf), robust Dodonaea viscosa ssp spathulata, (spoon shaped leaf), the attractive Dodonaea viscosa ssp angustissima, (delicate linear leaves), the arid area Dodonaea viscosa ssp mucronata (pointy tipped spoon-shape leaves) and the appealing purple leafed screening or accent favourite from New Zealand Dodonaea viscosa ssp purpurea.
Recently variegated and prostrate forms of Dodonaea viscosa ssp spathulata have proved very popular as landscape features and accent plants. All the above species form excellent water wise informal screens or formal hedges (biennial pruning necessary). Some of the most classic forms of these plants can be enjoyed in very exposed sites such as sea cliffs
or frontal dunes where the wind shearing effect has resulted in unique and photogenic botanical marvels.
Hop Bushes are unusual members of the Soapberry family
There are 66 Dodonaea species, elevating it to being the largest genus of the 150 genera Soapberry family Sapindaceae, ('Sapo' Latin for soap). Many family members contain a saponin glycoside, which provides plants with useful detergent-like foaming attribute acting to reduce the water tension when shaken under water. In contrast to open dry woodlands where Hop Bushes flourish, most of the family members are found in closed, tropical forests, being prized for their well known fruits. These include the luscious Lychee litchi chinensis and Rambutan Nephaleum lappaceum along with the sticky sweet Asian delights from the Tamarind seed pods Tamarinus indica. All these tropical members attract the pollination services of a variety of insects and birds by boldly marketing their flowers with alluring nectaries, scents and colours. Their irresistible fruits ensure the forest fruit eaters disperse their seeds far and wide.
Dry, exposed woodland communities enhance their long term survival
In contrast to the families main pollination process the Hop Bush is surprisingly a wind pollinated plant. The Dodonaea floral structure, colour and lack of scent provide cryptic clues in this regard and help in understanding why it flourishes in dry, exposed vegetation communities. Missing from the flowers are the obvious bold coloured petals, sweet chalices of nectar or alluring scent essential for the tropical family members to advertise their rewards in exchange for insect or bird pollination services. Closer observation reveals that the flowers are at the ends of branches with their stigmas having a broad sticky collecting surface ideal for catching airborne pollen. With disproportionate numbers of anthers (relative to stigmas) they are capable of wafting clouds of fine yellow pollen into the breeze where they can travel some two kilometres during their pollination season. ( West, Judy, A Revision of Dodonaea Miller (Sapindaceae) in Australia, Brunonia, No.7, 1984.) As obvious wind pollinated flowers they thrive in exposed, dry landscapes allowing the wind to do its job.
By establishing itself in prominent single species groves within low diversity, open plant assemblages, Hop Bushes, like other wind pollinated native trees and shrubs, such as She-oak (Allocasuarina verticillata) and North-Esk Pine (Callitris oblonga) improve their chances that the pollen will reach its target. Like Hop Bushes, these species are dioecious
having male and female flowers on separate plants. It is also interesting to note their pollen transfer occurs when the warm dry breezy conditions of late spring to early summer arrive after the rainy, humid conditions have waned.
Hop Bushes enhance Bird and Insect diversity
Hop Bushes' three dimensional twiggy and leafy frameworks are an open invitation for the wheel webbing spiders to weave their intricate webs to capture unsuspecting passing insect prey. These webs are diligently collected for binding the fibrous grass strands during nest building by insect and seed feeding birds such as Brown Thornbills, Flame, Scarlet and Dusky Robins, Welcome Swallows, Strong-Billed and Black Headed Honey Eaters, Grey Fantails, Eastern Spine Bills and Dusky Wood Swallows. Other large seed eaters such as Bronze winged Pigeon, Beautiful Firetail (Tasmania's only native
Finch), Musk Lorikeet and Green and Eastern Rosella devour the nutritious winged seed clusters before they are either feasted on by seed weevils or glide to ground. Mid-storey bushes like Hop Bush and Native Box (Bursaria spinosa) planted into the park style urban landscapes and gardens provide an important role in helping to attract these seed and insect eating birds at the expense of the aggressive domineering nectar feeders such as New Holland Honey Eaters, Noisy Minas and Wattle Birds.
Seeds are protected by Ants
Once the Hop Bushes release their seeds onto the ground, ants have co-evolved a mutually beneficial process to assist their survival from both fire and seed predation. This symbiotic relationship relies on the attraction to the ant of the nutritious fleshy attachments (elaisomes), which they busily collect and subsequently secrete a couple of centimetres below the woodland's floor. Here protected from the surface environmental vagaries they serve as an underground larder. This process of dispersing seeds by ants has the descriptive name of myrmecophory (myrmex Latin for ant). Interestingly the notorious
Bull Ant and Jack Jumper (Myrmex sp.) as well as the rare diurnal termite ant-feeding Banded Ant Eater (Myrmecobius fasciata - Numbat) have this prefix represented in their name. Once abandoned these piles are poised to respond to moisture and heat from surface bush fires which crack their hard coats, enabling a germination flush. Critical to the survival of the seedlings is the requirement that their roots establish a symbiotic relationship with mycorrhizal fungi. These fungi act as 'soil postmen' supplying (posting) water and nutrients to the plant's roots which in turn provide, via their ability to photosynthesise, a supply of carbohydrates to the fungi.
Hop bushes are culturally significant
Both aborigines and colonists valued Hop bushes for their cultural and medicinal properties. So impressed were the early colonists with the similarity in looks and taste, which its winged seed capsules had to hops, they were inspired to successfully brew a tangy, bitter but drinkable beer. The name 'Hop bush' still remains its popular common name.
From a cultural perspective aboriginal tribes knew the plant as the 'Oyster Bush' since once the winged seed capsules had deepened in colour to reddish-orange, they knew the bounty of succulent oysters from the nearby rocky estuarine foreshores were in peak condition ready for harvesting.
Hop bushes are medicinally important in all the widely separated countries where it grows. It is uncanny that similar cultural and medicinal uses have evolved from the local indigenous populations in each of these disparate countries.
This is revealed by findings from recent pharmacological analyses of hop bushes which reveal a common set of active ingredients represented by alkaloids, tannins, flavonoids, organic acids and 1-8 cineole rich oils. The variations in its medicinal usage relates to changes in relative concentrations of these ingredients, which are determined by soil types and environmental conditions typical of the countries and habitats in which they occur. Within each country another variation in relative potency of active ingredients is also related to seasonal differences at the time of harvest. Although the Hop Bushes are found in many distant countries, it is uncanny how unrelated local indigenous populations have attributed similar cultural and medicinal uses to this ubiquitous species. The following paragraph highlights some of its key medicinal uses.
Hop Bushes are valued for medicinal applications
Common amongst the older aborigines were the persistent problem of toothache derived from decades of grinding highly fibrous diets. By chewing the leaves of the Oyster Bush, mild analgesic and euphoric effects provided much sought after relief from nagging toothache. Aboriginals used the term 'Pitori' for plants such as Hop Bushes that acted as painkillers.
Inflammations from rashes and bruises as well as jelly fish and stonefish stings were eased by binding wads of chewed leaf pulp for a few days on the affected areas. The bitter juice exuded from the leaves during the preparation of these wads was not swallowed but collected as an antiseptic. In general the leaves were known to reduce inflation and swelling as well as impart an antimicrobial protection to open wounds and infected sites.
The Central Australian Aborigines (like indigenous Indian tribes) were reported to rely on the leafy branches as a customary means for relief of flu like fever and body aches. The leafy branches were smoked on warm ash beds releasing 1-8 cineole rich oils (well known active ingredient in the essential oils extracted from Gum, Eucalyptus sp., Tea Tree Leptospermum sp.,
Paperbarks Melaleuca sp. and native mint bush Prostanthera sp). The smoke would act as a febrifuge (fever reducing agent) by reducing the swelling of mucous membranes and loosening phlegm thus freeing the airways.
Also common amongst colonists and aboriginals were digestion and elimination problems. This was a result of hot weather, poor food hygiene and sub standard nutrition. Australian aboriginals, in parallel with indigenous cousins from North America, Mexico and South Africa used the tannins (dried stems/leaves contain 14% tannin compared with Black Wattle bark, Acacia mearnsii - 45%, - the favoured species of the early tannin industry) and flavonoids properties of the Hop Bush by applying poultices of fresh leaves, to relieve diarrhoea, stomach and uterine cramps. The typical mode of action has been reported in pharmacological studies to act by sedating smooth muscle contractions.
Interestingly, across the south east, Australian Aborigines preferred to construct their temporary shelters from D. viscosa var. angustissima simply because the outer side of the dead branches retained their leaves.
Culture uses in other countries
It has been recorded that the South American Peruvian Indians developed a culturally accepted practise of chewing the Hop Bush leaves in the knowledge that it acted as a valued substitute for Coca (Erythroxylum coca). Like betel nut, the younger viscous (sticky appearing) leaves were often chewed with ash, lime or magnesia to neutralise the organic acids binding the active ingredients, thus enhancing its stimulant and euphoric effects. Of course, akin to betel nut chewers, the lime would have caused rapid tooth decay.
Like its companion woodland plants, She-oak, Allocasuarina sp, Native Box Bursaria spinosa, and Black Wattle, Hop Bushes are often disregarded as common uninteresting mid-storey species. However this new brew of information in relation to its rich tapestry of cultural use and interrelationship, hopefully will entice a more in depth appreciation and further use as a valued revegetation or landscape framework species.
Whiting, J., et al., 2004. Tasmania's Natural Flora. Tasmania's Natural Flora Committee;
Van Wyk, Ben-Erik, 2003. Gericke, N., People's Plants,. A Guide to Useful Plants of Southern Africa. Briza Publications.
The Collection Newsletter Volume 6, Issue 1, 2004. Dodonaea viscosa Hop Bush www.tcbmed.com/newsletters/volume6-Issue1
Closs, J Dodonea Study Group 1993 Dodonaea Australian Plants Journal 17/137
Latz Peter, Bushfire and Bush Tucker, Aboriginal Plant use in Central Australia.