White Weeping Broom

Retama raetam (Forssk.) Webb

Synonyms - Genista raetam

Family: Fabaceae

Names:

Other Names:

Bridal Broom.
White Spanish Broom.

Summary:

A deciduous, tall perennial shrub to 3 m high and 6 m wide with many slender grey green, usually leafless stems that droop. Prolific sprays of white flowers are produced in late winter to early spring in sandy coastal areas.

Description:

Cotyledons:

Two.

First leaves:

Leaves:

Alternate, spiral, subsessile.
The leaves are small and quickly dropped, leaving the plant leafless for most of the year.
Stipules - None.
Petiole - 0.5 mm
Blade - Small and narrow, 5-6.5 mm long x 0.5-1 mm wide. Parallel sides, base tapering, tip pointed. Hairy.

Stems:

Usually multi stemmed. Stems to 20 mm thick and over 3 m long. Pendulous especially when in flower. Young stems are hairy and become hairless with age.
Leafless for most of the year.
Smooth or slightly grooved, striped grey green bark

Flower head:

Flowers formed close to the stem in clusters of 3-15. Raceme.
Flower stalk (pedicel) 1-1.5 mm long.

Flowers:

White with a maroon calyx, pea type, 8-10 mm long with a sweet, honey fragrance.
Ovary - Superior, 1 celled. 2 ovules per cell.
Style - 1. Simple.
Sepals - 5. Joined. 3-4 mm long
Petals - 5.
Stamens - 10. Free of the perianth in a closed sheath.
Anthers - Anthers dehiscing via longitudinal slits.

Fruit:

Globular to oval pod, non fleshy, 10-15 mm diameter x 7-10 mm long with 1-2 seeds. Hundreds of pods per mature plant. The pod usually remains intact (indehiscent) but some split to release the seed.

Seeds:

Yellow, green, brown or black. Kidney shaped, 6.5 mm long

Roots:

Strong taproot

Key Characters:

Leafless stems or with small linear leaves.
White pea type flowers with a maroon calyx and a sweet fragrance.
Globular to oval pod, ~10 mm with 1-2 kidney shaped seeds.

Biology:

Life cycle:

Seeds germinate mainly in late autumn to winter to form a wispy single stemmed plant. It takes 2 years for the first flowers to appear in spring. Pods form a month later. The seed is initially dormant and it may take some years for the hard seed coat to soften and allow the seed to germinate. Extra stems appear with time to form a multi stemmed plant. Plants will re sprout if damaged mechanically or singed by fire. Masses of seedlings often emerge after fire.

Physiology:

Fixes atmospheric nitrogen.
Very drought tolerant.

Reproduction:

By seed.

Flowering times:

July to November in WA.
July to October in SA.

Seed Biology and Germination:

Seed forms from October to December and seed drop occurs from November to January.
Germination may occur at any time of year with a flush from April to June and reasonable numbers in July and August.
Large numbers of seed are produced.
Seed has a hard seed coat and most seed is initially dormant.
Seed remains viable in the soil for at least 5 years and probably in the order of 20 years.

Vegetative Propagules:

Coppices from the base when cut.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Seed spread by water, soil movement, garden waste rabbits and possibly ants.

Origin and History:

Native to the dry dessert grasslands of the Mediterranean region (Northern Africa, western Sahara, Sicily and the Middle East.
Introduced to South Australia before 1841.
It is the "Juniper" referred to in the Old Testament.

Distribution:

SA, WA.

Courtesy Australia's Virtual Herbarium
Naturalised in the United States and Great Britain.

Habitats:

Climate:

Mediterranean.

Soil:

Sandy, low fertility to fertile, well drained alkaline soils often in coastal areas.

Plant Associations:

She-oak (Allocasuarina) woodlands. Forest. Low sclerophyll shrub-land

Significance:

Beneficial:

Ornamental. Used for roadside plantings and dune stabilisation in the past.

Detrimental:

Invasive environmental weed (It is in the top ten invasive garden plants in south west WA and on the Australian National Alert List for Environmental Weeds.)
Occasionally infests grazing land.
Potential weed of pastoral areas.
Poor palatability.

Toxicity:

Leaves, flowers and fruit are toxic.

Symptoms:

Respiratory failure.

Treatment:

Legislation:

Importation of seed and plants is banned.

Management and Control:

Seedlings can be pulled up but juveniles and larger plants are difficult to pull due to their long taproot.
Spray with triclopyr600 in winter and spring at 1:100.
Treat stems with triclopyr600 in diesel at 1:50.
Cut then paint stems immediately with neat glyphosate360.
Hot fires can kill plants and encourage seed to germinate.
Slashing and mowing are ineffective as it regrows (coppices) from the base.
Plant Australian native broom (Viminaria juncea) as an alternative ornamental broom.

Thresholds:

Very low because it hasn't established in most areas and is likely to spread.

Eradication strategies:

Treat mature plants as above.
Hand pull or spray seedlings at least every second year before any seed is set.
If possible, burn the site to encourage seed to germinate.
Treatment will need to be continued for 10 or more years on most sites.

Herbicide resistance:

None reported.

Biological Control:

Related plants:

Retama monosperma is a garden plant and potential weed.

Plants of similar appearance:

Spanish Broom (Spartium junceum).

References:

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (2007). Western Weeds. A guide to the weeds of Western Australia. (Second Edition). Plant Protection Society of Western Australia, Perth, Western Australia. P162. Photo.

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #848.1.

Paczkowska, G. and Chapman, A. (2000). The Western Australia flora: a descriptive catalogue. (Wildflower Society of Western Australia (Inc), the Western Australian Herbarium, CALM and the Botanic Gardens & Parks Authority). P445.

Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn). P. Photo.

Acknowledgments:

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