African Thistle Berkheya rigida (Thunb.) Ewart, Jean White B. Rees.
Synonyms - Stobaea rigida.
Family: - Asteraceae.
Names:
Berkheya - celebrates the Dutch botanist Le Francq van Berkhey.
Rigida is from the Latin word meaning rigid or stiff and refers to the somewhat woody stem or the sharply pointed spines.
African Thistle - refers to its country of origin.
Other Names:
Augusta Thistle - refers to the Augusta locality near Hamelin Bay in WA.
Berkheya Thistle
Hamelin Thistle - refers to Hamelin Bay in W.A. where it was introduced as ships dumped ballast before loading timber.
Summary:
Rhizomatous, woolly haired, yellow flowered, spiny perennial thistle with annual tops. It is erect, somewhat woody, 300-1000 mm tall and often roots at the nodes forming colonies. Yellow flowers are produced from late spring to autumn.
Description:
Cotyledons:
Two.
Leaves:
Form rosettes.
Petiole - almost none.
Blade - 30-100 mm long by 20-40 mm wide. Blue green colour with a whitish bloom on top. White with woolly hairs underneath. Stiff. Taper toward base. Lobed almost to the midrib. Lobes parallel sided to triangular and rolled inwards with very sharp points. Lobes twisted so they are at right angle to the plane of the leaf.
Stem leaves - Alternate. Shorter than rosette leaves. The ones near the top are very short and the blades run down the stem as spiny wings.
Stems:
Blue green. Erect or spreading. Woolly hairs especially near the base. Form roots where they touch the ground. Up to 1000 mm tall.
Flower head:
Daisy type, on a short stalk. Terminal and in leaf axils, disc shaped. 30-40 flowers in the head. Yellow. Several rows of bracts underneath, are spreading, very sharply pointed, with the edges rolled inwards and several pairs of 7-12 mm spines.
Flowers:
All bisexual, tubular. 5 lobed. Central disc flowers are yellow like the peripheral flowers that have the petal like rays.
Ovary -
style - has parallel sided branches.
Receptacle - Honey combed with stiff scales that are joined and deeply cut.
Petals - Yellow.
Stamens -
Anthers - Arrow like (sagittate) at the base.
Fruit:
Achene.
Seeds:
Black. 2.5-3mm long. Smooth (or ribbed according to Black, 1965). Hairless to almost hairless. Conical. Pappus is a crown of minute, soft, toothed scales. Large numbers produced. Retained in pitted pockets in the receptacle.
Roots:
Creeping. Short and thick with several strong rhizomes and a much branched network of feeder roots near the surface.
Key Characters:
Styles not swollen in the middle. Anthers sagittate. Receptacle scaly.
Biology:
Life cycle:
Perennial. Seeds germinate in autumn and produce a rosette of leaves. Top growth is initially slow as an extensive root system is formed. Several flowering stems form in spring. Flowering starts in October and will continue to May if moisture is available. Top growth dies with the onset of drought or in early autumn. In late autumn new rosettes arise from the old crown or rhizome buds.
Physiology:
Reproduction:
By seed, rhizomes and rooting from fallen stems or fragments.
Flowering times:
October to May. January to May in Perth.
Seed Biology and Germination:
Seed remains viable in the soil for many years.
Vegetative Propagules:
Creeping rhizomes.
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
The seed remains in the spiny head that falls to the ground and is entangled in passing animals or clothing for transport. Rhizomes extend underground slowly increasing the size of the colony. Stems fall over and take root where they touch the soil.
Origin and History:
South Africa.
Probably introduced to WA at the turn of the century when ships dumped ballast before loading timber. It was first recorded at Geelong in Victoria in 1906.
Distribution:
SA, TAS, VIC, WA.
Habitats:
Climate:
Sub-humid warm temperate to sub-tropical scrubland.
In Australia it occurs mainly near the coast in SA, Tas. and WA. Overseas it occurs at inland sites also.
Soil:
Sandy coastal soils and light soils to loams in inland areas.
Plant Associations:
Scrub lands.
Significance:
Beneficial:
Detrimental:
It is too spiny and woody to be grazed.
Large colonies can prevent access to pasture and recreational facilities.
Strict control measure have kept this weed a potential rather than actual problem.
Toxicity:
Not recorded as toxic.
Legislation:
Noxious weed of WA and TAS.
Management and Control:
Thresholds:
Eradication strategies:
Hormone herbicides have been used to control most infestations. Spring application before flowering is used. Single plants should be removed mechanically and burnt. As much of the rhizome as possible should also be removed.
Herbicide resistance:
None reported.
Biological Control:
Related plants:
None.
Plants of similar appearance:
Thistles from the Cynareae family. These may be distinguished by there styles that are swollen near the middle, their anthers that are distinctly tailed and the lack of scales on the receptacle.
Creeping Thistle also has a rhizomatous root system.
References:
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P891.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #169.1.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P661-662.
Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P151-153. Diagram. Photo.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P184-185. Photos.
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.