Dune Onion Weed

Trachyandra divaricata (Jacq.) Kunth

Synonyms - Anthericum divaricatum.

Family: Asphodelaceae.

Names:

Trachyandra
Divariacata refers to the divaricate or widely spreading branches of the flower stem.

Summary:

Dune Onion Weed has clumps of drooping, flattened, somewhat succulent, strap-like leaves, 350-450 mm long, emerging from underground rhizomes. The many and widely branched, stout, somewhat sprawling flowering stems carry white, 6 'petal' flowers. The “petals” are 4-14 mm long with a brownish or purplish central stripe and have two yellowish spots near their base. It has 6 stamens with yellowish anthers and a slender unbranched style. It has little or no odour.
Native to South Africa, Dune Onion Weed is often found on limestone soils as a weed in dunes and coastal heath along the south and west coast in WA, mainly from Albany westwards. It flowers in late winter and spring and is toxic to horses.

Description:

Cotyledons:

One.

Leaves:

Several, arising from the base. Enclosed at the base by brown-purple membranous scales. No aroma.
Blade - Parallel sided, strap like, 350-450 mm long x 2.5-5 mm wide, flat, thick, drooping, weak, rough to touch, about the same length as the flowering stems. Shiny. Pointed tip. Parallel sides. Sheathing base. Hairless or with tiny hairs (papilla).

Stems:

Rhizomatous.
Flower stem - Scape - Smooth, stout, round, leafless, 350-450 mm tall, widely branched and often repeatedly branched towards the top. Enclosed at the base by brown-purple membranous scales. Hairless.

Flower head:

Many flowers, each in the axil of a bract, along the branches on erect, 5-10 mm long stalks (pedicels). The pedicels are jointed just below the flower.

Flowers:

Ovary - 12-20 ovules per cell. Thread like style. Stigma small, smooth edged.
'Petals' - Perianth segments, 6, free, equal segments, white with a green or purple vein and usually with 2 yellow spots near the base of each segment. Segments 8-12 mm long, bent back. Falls off after flowering.
Stamens - 6, yellow, outer 3 bent back, inner 3 pressed against the ovary at the base. Filaments with short hairs at the base and tiny downward pointing bristles near the top. Attached to the base of the 'petals'.
Anthers - 6, yellowish.

Seeds:

Brown or grey, angled.

Roots:

Slightly thickened at the base and tapering. Fibrous. Rhizomatous.

Key Characters:

Leaves and scapes enclosed at the base by brown or purplish membranous tubular scales.
It does not smell like onions.
Adapted from T.D. Macfarlane.

Biology:

Life cycle:

Perennial.

Physiology:

Reproduction:

By seed and rhizomes.

Flowering times:

September and October in Perth.
Spring in WA.

Seed Biology and Germination:

Vegetative Propagules:

Perennial rhizome.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spread mainly by seed. Invades bushland and pastures after fire, disturbance or overgrazing.

Habitats:

Climate:

Temperate. Mediterranean.

Soil:

Most abundant on sandy limestone soils.

Plant Associations:

Inter dune beach heath land.

Origin and History:

South Africa.

Distribution:

NSW, SA, WA.
WA - South west of WA from Geraldton to east of Albany.

Courtesy Australia's Virtual Herbarium.

Significance:

It is rapidly spreading along the coast in WA.

Beneficial:

Honey plant.

Detrimental:

Weed of pasture, bush land, coastal heath, roadsides, islands and disturbed areas

Toxicity:

Relatively unpalatable and generally causes few problems where adequate feed is available. It is toxic when grazed. It appears to be toxic to most stock and most cases are recorded in horses.

Symptoms:

Stiff, stumbling, uncoordinated gait, tremors and sweating leading to partial paralysis. Muscular ability but not sensation are affected. Animals tend to collapse on their sternum and death from dehydration, starvation or complications of paralysis follows. It may take 1-3 months for the symptoms to progress.

Treatment:

If detected early and stock are removed from the infestation then partial or full recovery follows. In most cases it is detected too late and the disease runs its course.
Remove plants or ensure adequate feed is supplied in infested paddocks and remove stock if there is any evidence of grazing on the plant.

Legislation:

None.

Management and Control:

Blanket wipers applying glyphosate and metsulfuron have given good selective control in pastures.
Blanket wiping with 1 g metsulfuron per litre of water can provide fairly selective control in clover based pastures.
Spinnaker at 100 mL/ha in autumn provides 50-70% control of Dune Onion Weed seedlings, reduces grasses and has little effect on legumes. Higher rates only improve control marginally and cause more damage to pasture grasses.
Repeated mowing gives some control.
Cultivation in summer provides good control.

Thresholds:

Eradication strategies:

Manually remove isolated patches before flowering.
Cultivate in summer to kill old plants and repeat in the following summer to control seedlings that have established. Cultivation when the soil is wet is usually ineffective.
Wick or blanket applicators or sponge gloves, using 5 g of metsulfuron(600g/kg) or 500 mL of glyphosate(450g/L) plus 2.5 mL wetting agent per litre of water are useful in sensitive areas. Apply before flowering. Larger areas can be sprayed with 20 g/ha chlorsulfuron(750g/kg) plus wetting agent or hand sprayed with 0.4 g chlorsulfuron(750g/kg) plus 25 mL wetting agent in 10 L water in winter or spring when the plants are actively growing. This will kill most annual legumes and the seedlings of some native plants.
Replant shrub and tree species.

Herbicide resistance:

None reported.

Biological Control:

Related plants:

None.

Plants of similar appearance:

Onion Weed (Asphodelus fistulosus) is similar and grows in similar locations. It is distinguished by its hollow cylindrical leaves.

References:

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P22-23. Diagrams.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1217.1.

Marchant et al (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia).P779.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.