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South African weed orchid: Identification | LC0273 |
Jill Fleming (Horsham)
December, 2002 |  |
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This Landcare Note describes the identification of the South African orchid, Disa bracteata (Monadenia bracteata).
Common and scientific names
South African weed orchid, African weed orchid, South African orchid or Brown finger orchid. Disa bracteata (Sw.) T.Durand & Schinz. Family Orchidaceae (orchids).
Status
South African orchid is not a proclaimed species anywhere in Australia. The weed is identified as a New and Emerging weed in the Wimmera Weed Action Plan 2000-2005, with 1 ha currently infested in Wimmera Catchment Management Authority region. It gained this status after being identified as a significant threat to environmental values and all known infestations in the Wimmera could be treated within three years to achieve containment and/or eradication. The weed has potential to impact on native understorey flora, especially rare and endangered plants.
There are five main infestation sites in Victoria; Black Range – Stawell, Lake Eppalock – Bendigo, Deans Marsh – Otways, Rowsley Valley – Bacchus Marsh and the Lower Glenelg National Park, which are currently under a control and monitoring program. The other known infestations throughout the state have been contained and have long term monitoring programs in place.
The weed is likely to be introduced accidentally on vehicles and machinery due to poor hygiene practices, spread by seeds on clothing, shoes and camping equipment, and by wind dispersal.
The plant grows readily in competition with a wide range of other flora including grasses, it invades bushland and pastures and is attracted to disturbed sites. The South African orchid will grow in all light conditions and is not fussy about soil types.
Figures 1. South African orchid, showing flowering and vegetative parts.
Figure 2. South African orchid infestation sites in Victoria.
Background and distribution
The largest family in the world, orchids represent nearly a tenth of all flowering plants. Orchids occupy a diverse range of habitats and are most diverse and abundant in the moist tropics. They are important ecologically having symbiotic relationships with soil fungi and most are dependent on specific insect pollinators. Unlike our threatened native orchids, D.bracteata is self-pollinated and each plant produces tens of thousands of airborne seeds.
In its native South Africa, it grows in the Cape Province – home to many of our weeds, from sea level to 2000m. It was first noticed naturalised near Albany, Western Australia in 1944, where it now invades several thousand square kilometres. The 1990 records show it spreading as far north as Geraldton and east to the Israelite Bay.
D.bracteata first appeared in South Australia in 1988, spreading rapidly in the 1990’s. It is believed to have escaped from orchid enthusiasts, where it was cultivated as a curiosity. In South Australia, the problem has at least doubled annually and the local spread has averaged some 10km/yr north and south. Current knowledge is that there are at least 10 ha infested in Victoria. The first recorded infestation in Victoria was in the Rowsley Valley near Bacchus Marsh in 1991. Infestations in Victoria are also likely to be the result of garden escapes.
Identification/Description
South African orchid is a deciduous perennial terrestrial orchid with underground tubers. Dormant for much of the year, it sprouts in early spring and takes a minimum of three years from seed to flowering stage.
Stems – Erect and fleshy usually 30 – 50cm tall.
Leaves – Leaves numerous with parallel veins, decreasing in size progressively up the stem; lower leaves 5-15cm long, tapering from a broad base to an acuminate apex.
Flowers – from late October through to December in Victoria. 15-30 on a thick cylindrical spike 5-20cm long, which resembles a greenish-brown asparagus spear. Flowers very dense, arranged in an indistinct spiral, mostly reddish-brown and yellow with a leafy bract.
Figure 3. A flowering stem of South African orchid.
Seeds – black, minute and dust-like, contained within the capsular fruit. The species is autogamous (self-pollinating) and thus produces a large amount of seed per plant. The seeds may be blown many km and can remain viable for seven years. Seed set and dispersal starts at the end of November. The seeds continue to mature in the capsule if the flower head is picked and the capsule shatters and disperses them when ripe.
Tubers – Generally thought to have 1–3 tubers, similar shape to a garlic clove or bulbs, about 20mm in size. The plant also has a mass of fleshy side roots and there is no main tap root.
Figure 4. Tubers and vegetative parts of South African orchid.
If uncertain about the identification consult the keys to the Orchidaceae in the Flora of Victoria (Volumes 2 and 4) or submit specimens to the Herbarium of Victoria.
Further information
See the Landcare Note: South African weed orchid – management, for a information relating to the control and management of this plant.
For further technical advice please contact a Catchment Management Officer at your Department of Natural Resources and Environment office.
References
- Backhouse, G. (2000) The occurrence of the South African orchid Disa bracteata Sw. in Victoria. Austral. Orchid Review 65(5), 22.
- Jessop, J.P and Toelken, H.R, (1986) Flora of South Australia Part IV. Adelaide, South Australian Government Printer.
- Marchant, N.G. Wheeler, J.R. et al (1987) Flora of the Perth region, vol 2, Western Australian Herbarium, Department of Agriculture, Perth, WA.
- Walsh, N.G and Entwisle, T.J. (1994, 1999) Flora of Victoria Volumes 2 and 4. Melbourne, Inkata Press.
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Acknowledgments
Prepared by Jill Fleming with the kind assistance of Ian Faithfull (Keith Turnbull Research Institute), Stuart Lardner (NRE Horsham), Mark Farrer and Celeste Ellice (NRE Stawell), Kate Blood (Weeds Cooperative Research Centre). Photographs by David Venn (NRE Horsham).
Find more information about NRE on the internet at http://exwb01.nre.vic.gov.au/ or call the NRE Customer Service Centre on 136 186.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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