Cirsium is from the Greek word kirsion or thistle, which probably meant 'swollen vein', referring to the injury caused by the spines.
Vulgare is from the Latin word vulgaris meaning common.
Spear Thistle refers to its spiny nature.
Other Names:
Black Thistle
Bull Thistle (North America)
Fullers Thistle (UK)
Karmedik (South Africa)
Scotch Thistle (NZ and WA)
Shaapdissel (South Africa)
Swamp Thistle
Summary:
Spear Thistle is a spiny, large headed, purple flowered annual to biennial thistle to 1.5 m tall. The basal leaves are hairy, deeply dissected and spiny and the lobes are twisted at right angles to each other. The stem leaves continue down the stem as spiny, narrow wings. Large, single or occasionally clustered, purple thistle type flower heads up to 4 cm in diameter are produced at the ends of the stems from October to May. The fruits are topped by soft feathery bristles. Native to Europe and western Asia, Spear Thistle is a common weed of pasture, roadsides, waste land and disturbed bushland.
It is sometimes incorrectly called Scotch Thistle.
Description:
Cotyledons:
Two. Club shaped. 15-20 mm long. Tip round. Base tapered. Hairless. No petiole.
The seedling has a short hypocotyl and no epicotyl.
First leaves:
Club shaped. 20-25 mm with a short merging petiole. Tip pointed slightly. Short stalk. The upper and lower surfaces and petiole have multicellular hairs . Edges spiny. The leaves are produced singly and usually have scalloped edges rather than lobes.
Leaves:
Forms a flat, basal rosette.
Petiole - On rosette and lower stem leaves.
Blade - Dark green on top , white underneath, lance shaped to oval, up to 350 mm long, fleshy, rough to touch. Usually 4-6 lobes indented about half way to the midrib. Spiny on upper surface. Lobes end in long 2-15 mm, sharp, rigid spines. Lobes twisted at right angles to the leaf may also be lobed into 3 or 4 more divisions. Upper surface with few cobweb hairs and warts from which sharp spines emerge. Lower surface matted with hairs. The edges are spiny.
Stem leaves - Alternate, dark green on top white underneath. 100-250 mm long, rough to touch. 1-4 deep lobes with sub lobes that are erect and turned down sharply. Stem leaves are narrower than rosette leaves and the lobes are wider in proportion. Tip tapered with long 2-15 mm sharp, yellow spine. Leaf edges continue down the stem as wings. No petiole. Stout bristly hairs on top cobweb hairs below. Upper leaves are narrower and may have fewer lobes.
Stems:
Erect, polygonal, furrowed, pithy core and solid or with small hollow. Usually 600-1200 mm tall, up to 3000 mm overseas. One to several stems, branched near top. Spiny wings extend from the leaves down the stem. Stout hairs and woolly hairs. Usually formed in the second year of growth.
Flower head:
Panicle or corymb. Short to long flower stalks with a few reduced leaves below or none. Single or in groups of 3-4. On the end of branches. Involucre egg shaped to globular, 25-50 mm long by 20-50 mm wide, or up to 75 mm wide. Initially erect and becoming spreading with maturity.
Flowers:
Purple/red. All bisexual.
Bracts - Green base and pale top. Lance shaped to parallel sided, spine tipped, with pale bases many rows. Sparse to woolly hairy, rarely hairless.
Florets - Tubular. About 100 in each head.
Ovary - Hairy receptacle.
'Petals' - Purple red, spreading, stick out of the top of the flower head.
Stamens - Hairy filaments.
Anthers -
Fruit:
Achene. Straw coloured to grey, often with black or brown streaks, almost cylindrical, 3-6 mm long by 1.5-2 mm diameter. Smooth or slightly furrowed, hairless, slightly flattened, often slightly curved. Long, 20-30 mm, white feathery, branched, soft hairs, on a basal ring, attached to top of seed, fall off easily leaving a rim on the top of the seed with a raised, conical centre.
Seeds:
Roots:
Deep fleshy, branched taproot. Often dug up by rabbits.
Key Characters:
Flower head bracts end in a simple spine. Leaves rough to touch with small prickles on the upper surface.
Biology:
Life cycle:
Biennial or annual. Seeds germinate in autumn/winter and produce large rosettes and fleshy, branched, storage taproots. A few of the early germinating plants may flower in spring then die. The rest continue growth over summer and into the following season or until soil moisture is exhausted and the top growth dies off leaving the roots alive in the soil. In autumn, these roots form large rosettes that produce a flowering stem in spring and flowers in summer. The plant then dies with the onset of drought, but in moist areas these flowering plants may persist well into winter. In Tasmania, plants germinating is winter and spring tend to flower quickly in the following summer and autumn, thus acting as annuals. In other areas, it appears to be the early germinating autumn plants that behave as annuals.
Dead plants may remain standing for a year or two providing protection for seedlings below.
Physiology:
Reproduction:
By seed.
Flowering times:
October to May in WA.
Seed Biology and Germination:
Seeds germinate mainly in autumn but may germinate at any time of year that moisture is available.
It is generally considered to have short dormancy, but Canadian studies have shown that some seed can survive in forest situations for over 36 years.
Up to 200 flowering heads and 8000 seeds can be produced by a single plant. Most heads produce about 100 seeds.
Vegetative Propagules:
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
Wind, water, machinery, ants, attachment to animals and contaminated produce disperse seeds. Most seed falls close to the plant because the pappus usually falls off readily.
The major method of long distance dispersal is hay or contaminated pasture seed.
Infestations usually increase in density as the stocking pressure increases due to selective grazing of companions species.
Increased soil fertility and the introduction of legumes into the pastures system also increases infestations.
Field which are bare at the end of summer are the most prone to invasion by Spear Thistle.
Pugging due to overstocking wet paddocks during winter also encourages infestations.
There is considerable year to year variation in the density of infestations and this can usually be explained by the lack of competition from pasture plants when Spear Thistle seedlings are being recruited into the adult population.
It rarely invades dense perennial pastures.
Origin and History:
Europe, W. Asia, N. Africa.
First recorded in Tasmania in the 1830's.
In SA before 1841.
Distribution:
ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Habitats:
Climate:
Sub humid cool temperate up to sub alpine levels.
More abundant in the higher rainfall areas on mainland Australia and the medium rainfall Midlands area of Tasmania.
Prefers a long growing season.
Soil:
Prefers fertile soils that don't completely dry over summer or irrigated land.
Grey heavy clays and a wide range of other soils.
Plant Associations:
Black box, Myall.
Significance:
9.7 million hectares is infested in Victoria.
Beneficial:
Stock will eat seed heads only when green.
Roots used for making rabbit baits having the advantage that they are not particularly attractive to domestic stock.
Produces nectar and pollen for bees.
Extracts used in ancient herbal medicine for treating haemorrhoids.
Detrimental:
Weed of fallows, crop, pasture, bushland and wasteland.
Major weed of Rice in the Murrumbidgee Irrigation Area in NSW.
Contaminates wool.
Contaminates produce, hay and pasture and other seeds.
Injures stock.
Inhibits livestock movement.
Unpalatable and spiny. Often it is the only green material left in severely grazed areas.
Toxicity:
Spines may transfer infections such as scabby mouth in sheep and myxomatosis in rabbits.
Otherwise not recorded as toxic.
Legislation:
Noxious weed of NSW, SA, VIC and TAS.
Management and Control:
Cultivation, mowing, hoeing and stock management can provide reasonable control.
Thresholds:
In NZ, each Spear Thistle per square metre was estimated to reduce sheep live weight gain by 1.68 kg.
Eradication strategies:
Prevent seed set for several years.
It rarely persists under cultivation or in vigorous perennial pastures.
Phalaris appears to be more effective than cocksfoot for reducing the levels of Spear Thistle infestations.
In cropping areas herbicides and cultivation usually keep Spear Thistle at low levels.
In pasture areas, cultivate, spray and crop the area in the first year then sow a perennial pasture grass in the next. Manage stock to ensure good ground cover at the end of summer each year. Defer grazing in autumn to allow pasture competition to kill thistle seedlings. (Heavy grazing to kill thistle seedlings is sometimes used and it works best if combined with low rates of hormone herbicide as 1 L/ha 2,4-D amine(500g/L) in the "spray graze" technique when the thistles are young. Rotational heavy grazing is preferred to set stocking and care should be taken to avoid overgrazing the companion species.)
Grasses compete more effectively than legumes with Spear Thistle so ensure there is a vigorous grass as a part of annual pasture mixes.
Grazing with goats at flowering can reduce seed production.
Glyphosate provides good non selective control for pre cropping situations.
Clopyralid and a range of hormone and other herbicides provides high levels of control in various situations.
Mowing is not very effective because the plant tends to regrow from the rootstock. Manual removal is effective for small areas but unpleasant due to the spiny nature of the plant. Blanket wipers or wick applicators using 1 part glyphosate(450g/L) to 2 parts water can provide partially selective control. Overall spraying with 200 g/ha Lontrel®750 or 4 g Lontrel®750 plus 25 mL wetting agent in 10 L water provides reasonably selective control in bushland.
Isolated plants can be removed manually and a 5 metre buffer around the plant sprayed until just wet with 50 mL Tordon®75-D in 10 L water to help control emerging seedlings. This will damage most young broad-leaved species.
Cultivation is effective.
Grazing with sheep to reduce pasture then grazing with goats at flowering provides good control in 3 years.
Replant shrub and perennial species to increase shading in revegetation areas.
Herbicide resistance:
Biological Control:
A gall fly has been released in Canada and given good reductions in seed set but is unlikely to have a great impact. Some Nodding Thistle agents under investigation in Australia also attack Spear Thistle.
Related plants:
Perennial Thistle (Cirsium arvense)
Plants of similar appearance:
Spear Thistle can be distinguished from Slender, Perennial and Nodding Thistle in the young stages by spine bearing warts on the upper leaf surface, and the absence of a pale outline on the veins.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P94-95. Photos.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P933. Diagram.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P391-392. Diagram.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P723. Photo.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P30-31. Diagrams.
Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P44-45. Diagram.
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). #317.2.
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). P670.
Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P156. Photo.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P209-212. Photos.