Agriculture Victoria (2020). African thistle (Berkheya rigida). Victoria State Government. Available at: http://vro.agriculture.vic.gov.au/dpi/vro/vrosite.nsf/pages/weeds_african-thistle. [Accessed 1/12/2020].
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African Thistle (Berkheya rigida) is a rigid, spiny-leaved perennial (long lived) herb or sub-shrub growing to 60 cm or sometimes to 80 cm high. It possesses rhizomes (creeping underground stems) and often forms vegetative colonies shooting from these underground stems or by rooting at the nodes (stem joints) when stems come in contact with the soil. Young plants produced a basal rosette of leaves before producing a stem. All leaves are deeply divided almost to midrib forming lobes, upper surface blue-green or green with hairs soon lost, lower leaf-surface are whitish and densely wooly/hairy, with the tips of the lobes having sharp spines. Leaf margins revolute (the leaf edges rolled under towards the midrib). Rosette leaves are up to 100 mm long, 20-40 mm wide, larger than subsequent stem leaves. Mature rosettes produce an upright or spreading, branching stem, that is spineless, rather woody and often whitish and hairy (becoming less hairy with age). The stiff stem-leaves are alternately arranged, smaller than the rosette leaves, and the leaves are blue-green or green and hairless with age above.
The yellow flower-heads are 5-10 mm across, with several several flower-heads clustered at the ends of branches. The flower-heads are composed of numerous small tubular disc florets or flowers, surrounded by 3-4 unequal series of stiff, pointed and spiny leaf-like bracts (modified leaves), that are up to about 12 mm long. All flowers in flower heads are similar looking yellow disc florets that exceed the spiny flower-heads, with no ray florets (flower with large petals around the edge). Each flower produces a seed with many seeds produced on a flower-head.
The smooth fruits or 'seeds' (cypselas) are cone-shaped, 2.3-3mm long and blackish in colour. The larger end of these seeds is topped with a group of small scales called a pappus, all are joined forming a crown (Cooke 1986; Lander 1987; Lamp & Collet 1989; Hussey et al. 1997; Jeanes 1999; Parsons & Cuthbertson 2001; Richardson et al. 2006). Flowers most of the year (mainly spring and summer).
For further information and assistance with identification of African Thistle, contact the herbarium in your state or territory.
The natural habitat of African Thistle includes the subhumid warm-temperate to subtropical scrublands of southern Africa (Parsons & Cuthbertson 2001). It occurs as a weed in Australia, preferring lighter, sandy soils (e.g. infertile coastal sands) but also found on fertile loams and volcanic clays, growing on roadsides, in pastures and disturbed areas. African Thistle invades natural areas of forest, woodland, dune shrubland, coastal scrub e.g. in rocky foreshore areas and grassland (DPIPWE 2019; Lamp & Collet 1989; Parsons & Cuthbertson 2001; Thompson Berrill Landscape Design Pty Ltd 2006; Western Australian Herbarium 1998-).
African Thistle (Berkheya rigida) is distinguished from other daisies by its leaves being deeply divided into narrow lobes, each of which terminates in a spine, its stems not bearing spines, and its yellow thistle-like flower-heads that are basally surrounded by spiny bracts.
Saffron Thistle (Carthamus lanatus) also has yellow thistle flower-heads surrounded by stiff, spiny leaf-like, hairy bracts and deeply lobed leaves with each lobe ending in a spine, but it is an annual with its flower-heads 10-20 mm across and has larger spiny bracts (the outmost usually turned downwards).
Cultivated Safflower (Carthamus tinctorius) has undivided leaves.
Species of Centaurea with spiny yellow-flowered heads, e.g. Maltese Cockspur, also known as Malta Thistle, or Cockspur Thistle (Centaurea melitensis) and St Barnaby's Thistle (Centaurea solstitialis) have spineless leaves.
Golden Thistle (Scolymus hispanicus) has spiny, winged stems as well as having its leaves deeply divided into rigid, spiny lobes.
The Sowthistles Sonchus asper and Sonchus oleraceus have flower-heads lacking spiny bracts. (Lamp & Collet 1989; Auld & Medd 1992; Richardson et al. 2006).
African Thistle has no feed value, as its spines make it unpalatable to stock. It can form large colonies, consisting of matted stems. To date, it remains close to and on the coast. There is the potential for its wider distribution and impacts if African Thistle invades better soils away from the coast (Parsons & Cuthbertson 2001).
Agriculture: Large colonies, consisting of matted stems, limit pasture growth and available grazing area, reducing the productivity and economic returns of pasture areas. It is n0t grazed by stock and can invade sandy pastures (DPIRD 2020).
Native ecosystems: African Thistle can impact on biodiversity by competing with native species in natural areas, including coastal foreshores, dune areas, scrub and shrub-land, tussock grassland and woodland (Carr et al. 1992; Keighery & Longman 2004; Thompson Berrill Landscape Design Pty Ltd 2006; Western Australian Herbarium 2007). It has also been recorded growing in reasonably intact native vegetation in south-western Western Australia (e.g. in coastal areas near Augusta) (DEEDI 2020).
Urban areas: Dense patches can also impact on recreational areas and activities by preventing access to beaches and facilities (Parsons & Cuthbertson 2001). Depending on where plant is found, may impede access for humans. The spines are disconcerting to even well-seasoned bare feet and can be very disturbing if they penetrate blankets’ (Meadley 1956).
African Thistle (Berkheya rigida) reproduces from, and is spread locally by, rhizomes and rooting stems, and is spread great ditances by seed or rhizomes in containinated soil or on machinary. Colonies increase in size and density as a result of regrowth from rhizomes and layering of the long stems which take root when they bend downwards and come in contact with the soil.
African Thistle is spread across greater distances by seed, which may remain dormant in the soil for years. The seeds are not adapted for wind dispersal as they remain in the head (which functions as a burr) that falls to the ground at maturity. Because of the spiny nature of the burr, it may be caught up in the coats of passing animals and transported in that way, as well as being kicked along by hooves or moved by vehicles. Seeds fall from the burr and are dispersed as it is carried or rolls along (Lamp & Collet 1989; Parsons & Cuthbertson 2001).
African Thistle was first noticed in Victoria at Geelong in 1906 and Port Phillip in 1909, and in Western Australia at Hamelin Bay some time before 1914 (Parsons & Cuthbertson 2001). It is thought to have been introduced to Australia (particularly the colony at Hamelin Bay) from South Africa as seed in ballast from ships involved in the early timber trade. Dumped ballast at ports probably resulted in the scattered small colonies of this species in coastal southern Australia (Lander 1987; Lamp & Collet 1989; Hussey et al. 1997; Parsons & Cuthbertson 2001). There is also the possibility that it was transported across the Transcontinental Railway to South Australia from Western Australia (Kloot 1987).
Measures should be taken to avoid the introduction of African Thistle (Berkheya rigida) to new areas, and to prevent spread of existing infestations. Integrated management plans and control measures for African Thistle are available through the Western Australian Herbarium (1998–). Planning and implementation of an integrated control plan aims for eradication. A plan should include an inventory of African Thistle infestations in the area designated for control action, well-defined objectives, feasible control actions, follow-up actions, a realistic timeline and a budget, as a minimum.
Chemical control: Larger colonies can be chemically sprayed (Parsons & Cuthbertson 2001). Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au
Non-chemical control: Physical control: Hand remove isolated or small populations plants through spring and early summer.
Cultivation: Cultivation of the soils will break up rhizome and could spread the plant and should be avoided unless follow-up cultivation can occur until the energy in the rhizomes is exhausted, as African Thistle spreads via creeping underground stems and can form large colonies.
Fire: Single plants should be dug out and burned before flowering, making sure as much of the rhizome system is removed as possible.
Seeds germinate in autumn, and young plants produce a rosette of spiny leaves. Aerial growth is slow at first as plants establish an extensive underground system comprising a short rootstock, rhizomes and feeding roots. In late winter to early spring the growth rate increases and flowering stems form. Flowers can occur all year, but flowering occurs mostly during spring and summer, sometimes to autumn. Flowering through summer onwards will depend partly on the availability of moisture. Aerial growth dies in late summer or early autumn, and new shoots develop on the crown and from buds on the rhizomes in late autumn. Seeds may remain dormant in the soil for years (Hussey et al. 1997; Jeanes 1999; Parsons & Cuthbertson 2001; Richardson et al. 2006).
SA, VIC, WA
Although African Thistle (Berkheya rigida) is not widespread, it can be locally abundant. It occurs in a few coastal areas in south-western Western Australia including Perth, Bunbury, Hamelin Bay area, Cape Leeuwin and near Augusta.
In South Australia it is only known to occur in two location on the Eyre Peninsula, including Ceduna and Port Lincoln.
In Victoria it is known from many location around and surrounding Port Phillip Bay and west of Melbourne, including Port Melbourne and Bacchus Marsh, Geelong and Anglesea (AVH 2020; Hussey et al. 1997; Jeanes 1999; Parsons & Cuthbertson 2001; Richardson et al. 2006; Western Australian Herbarium 1998-).
African thistle established a population on King Island, but has since been eradicated. African thistle has not naturalised elsewhere in Tasmania (DPIPWE 2019).
African Thistle is native to South Africa (Parsons & Cuthbertson 2001).
Augusta Thistle, Berkheya, Berkeya Thistle, Hamelin Thistle.