Cirsium is from the Greek word kirsion or thistle, which probably meant 'swollen vein', referring to the injury caused by the spines.
Arvense is from the Latin arvum meaning 'cultivated field' and refers to the plants association with cultivation.
Perennial Thistle refers to its perennial nature.
Other Names:
Californian Thistle
Canada Thistle
Corn Thistle
Creeping Thistle
Perennial Creeping Thistle (UK)
Rankdissel (South Africa)
Summary:
The purple flowered, spiny mature plant is erect in habit with wingless stems that are sometimes branching and may reach 1 m in height. It has an extensive, creeping, perennial root system that produces annual tops.
Description:
Cotyledons:
Two. The cotyledons are 12 to 18 mm long and hairless. The petiole is absent or very short and merging. The seedling has a very short hypocotyl and no epicotyl. Tip rounded. Sides convex. Base tapered.
First leaves:
The early leaves are 15 to 20 mm long, have a short merging petiole, and are armed with spines around the margin. The upper leaf surface is a shiny green with the veins much paler in colour.
Leaves:
The plant develops as a rosette 200 to 300 mm in diameter.
Petiole - None.
Blade - Oblong to lance shaped, up to 150 mm long, deeply lobed ending in a spine. Edges spiny and crinkly or wavy. Hairless to somewhat hairy on top, woolly white on the underside.
Stem leaves - Alternate, 100 to 200 mm long, more deeply lobed than rosette leaves, sessile and semi-clasping, may extend down the stem as wings for a small distance. They carry few or no hairs on the upper surface, and a few downy hairs, or no hairs, on the lower surface.
Stems:
Erect, usually 600-900 mm tall, up to 1500 mm tall.
The stem is solid with a pithy core, polygonal in cross section, and may have shallow lengthwise grooves. Dark stripes are frequently present. The stem is hairless or may carry a few short stout hairs and some fine downy or cobwebby hairs. Sometimes branched, especially near the top.
Flower head:
Corymbose panicle. Male and female flowers are on separate plants (by partial abortion).
The inflorescences are composite and terminal on the stem in clusters of 1-5 heads and are not spiny. They are relatively long and narrow with a diameter of approximately 15 mm and a length of approximately 20 mm. They may have a short stalk or be stalkless. The male and female flowers differ slightly in shape.
Male flower head egg shaped, 12-20 mm long, may be hermaphrodite and set some seed.
Female flower head longer, 15-25 mm long.
Flowers:
The female flowers are strongly and sweetly scented.
Bracts - Many, closely overlapping. Outer bracts are short and sometimes tipped with a weak, often purple tipped spine. The inner ones are successively longer and narrower and have long tapered tips.
Florets - Tubular, pink to reddish violet or rarely white, ligulate (with 'petals')
Ovary - Hairy receptacle.
'Petals' - Pink to purplish.
Stamens - Hairy filaments.
Anthers -
Fruit:
Achene, 2.5-4 mm long by 1 mm wide, curved, four angled, slightly flattened, finely grooved, smooth, rather glossy surface, hairless. White, silky, feathery haired, pappus, 20-30 mm long, at the top falls off leaving a circular rim with a raised centre.
Seeds:
Light brown to olive green.
Roots:
Extensive, horizontal and vertical, creeping, branched, thickened, white or yellowish root system which send up erect shoots at irregular intervals. Up to 6000 mm deep, but most in the top 450 mm of soil. Roots may extend horizontally for more than 13 metres from the parent shoot.
Key Characters:
No wings or very short wings on stem where leaves join. Extensive perennial root system. Small pink flowers usually in clusters. No prickles on the upper surface of the leaves. Flower head bracts end in a simple spine.
Biology:
Life cycle:
Perennial. Californian Thistle produces separate male and female plants and infestations frequently consist of plants of one sex only. Fertile seed can be produced but spread by seedlings is considered to be of much less importance than vegetative reproduction. Seed germinates in autumn and spring and produces a vertical taproot. 2 months later roots are produced which grow horizontally initially then bend downwards. Aerial shoots often develop where the root changes direction. Most plants don't flower until their second season of growth. Regrowth from buds on the roots starts in late winter to early summer to form dense rosettes. Some of the rosettes produce flower shoots while others do not. Flowers do not normally appear until January or February. The aerial growth dies off in autumn, often after a frost, and it is normally dormant during winter. Roots will survive in soils frozen to 500 mm deep.
Physiology:
Reproduction:
By seed, root fragments and perennial roots.
Flowering times:
December to February in VIC, NSW, SA and TAS.
Seed Biology and Germination:
5-6000 seeds/plant produced overseas. In Australia, seed production is often limited by the separation of male and female infestations.
Seedling survival and recruitment is usually very low.
Seed may remain viable in the soil for over 21 years. Viability and longevity increase with depth of burial.
Germination is greatest in light, alternating temperature conditions.
Optimum depth for germination is 10 mm. Few seeds germinate if buried deeper than 50 mm or if left on the surface.
Vegetative Propagules:
Roots and root fragments.
A root fragment can produce plants covering 25 m2 in 2 years.
Hybrids:
There are several different forms and varieties. These differ in susceptibility to herbicides.
Allelopathy:
Old leaves and stems produces toxins that inhibit the growth of other plants.
Population Dynamics and Dispersal:
Spread can be by seed or vegetatively from the extensive creeping root system. Significant seed production only occurs where male and female plants occur with 100 m of each other. Many infestations are single sex and whilst male plants can produce limited viable seed the major source of spread in most cases is due to new plants arising from the perennial roots or root fragments.
Infestations can increase by several metres a year due to the expansion of the root system.
Cultivating equipment transports root fragments and this is an important form of spread within the field.
Seedlings only establish in bare areas where there is little competition.
Seed is not readily spread by wind because the pappus usually falls off. In wind dispersal studies, viable seed was blown about 10 m in a 29 kph wind and 60 m in a 46 kph wind. Field evidence in Tasmania indicates seed may move up to 1 Km by wind dispersal.
Seed will move in irrigation water and on farm machinery.
Long range dispersal is usually by seed as a contaminant of agricultural seed.
Origin and History:
Europe. Asia. North Africa. Possibly China and Japan.
First recorded and eradicated in WA near Geraldton in 1933.
Proclaimed as a noxious weed in VIC in 1885.
Distribution:
NSW, SA, TAS, VIC, WA.
Eradicated in WA and SA.
Californian Thistle occurs in most parts of Tasmania although it is somewhat uncommon in the Midlands. It grows most vigorously in the North-West and North-East in areas where the annual rainfall exceeds 1000 mm. It is frequently found throughout the Southern part of the State but in most years it does not develop large vigorous stands, its growth to a large extent being inhibited by the attack of the rust Puccinia punctiformis and aphids.
Habitats:
Up to sub alpine levels.
Climate:
Sub humid to humid cool temperate areas.
More abundant where annual rainfall exceeds 1000 mm in Tasmania and where rainfall exceeds 700 mm on the mainland.
Soil:
Prefers fertile, deep, loam soils
Plant Associations:
Prefers open situations.
Significance:
Beneficial:
Bees forage it.
Roots are edible.
After removing spines, young leaves have been used in salads and cooked as pot herbs.
Extracts used as a tonic, a diuretic, milk coagulant, a dysentery potion and to cause sweating.
Detrimental:
Weed of cultivation, vegetables, asparagus, potatoes, peas, irrigated and dry land crops, wheat, pastures roadsides, and disturbed areas.
Californian Thistle is economically important in pastures. It competes with pasture plants and restricts grazing due to its spiny nature. In crops, particularly irrigated vegetable crops, competes with the crop, causes harvest difficulties and contaminates produce.
Flower heads are difficult to remove from peas.
Causes injury to the mouths of sheep if forced to graze it.
Alternate host for some crop pathogens.
Pappus hairs may irritate eyes and skin on some people.
Toxicity:
Not recorded as toxic.
Legislation:
Noxious weed of NSW, SA, TAS, VIC, WA.
Management and Control:
Patches of 130 shoots/m2 are common.
Thresholds:
In North America heavy infestations reduce cereal yields by 40-70%.
In pastures in NZ economic gains occur when Perennial Thistle exceeds 30% ground cover.
Eradication strategies:
Cultivation must be repeated regularly over three years to be effective. Shallow cultivation in hot dry weather is preferred. Tined implements tend to spread root fragments that readily re grow.
Establishment of lucerne and regular mowing can be effective.
MCPB and 2,4DB applied at the budding stage appear to be the best of the hormone herbicides for control. Spray grazing is also used. Grazed plants appear to be more susceptible to herbicides than ungrazed plants.
Glyphosate, clopyralid, picloram, dicamba and chlorsulfuron are also effective in various situations.
Flooding to 150-200 mm deep with water for 3 months provides control in irrigation areas.
Grazing with goats is giving good control in NZ.
Covering with straw to 300 mm deep then turning the straw when shoots emerged to break then was is claimed to provide good control.
Combined methods are usually the best for controlling this difficult weed. E.g. Cultivate, crop and spray or Fertilise, slash and spray.
Herbicide resistance:
Strains resistant to 2,4-D occur overseas.
Biological Control:
A number of agents have been released in various countries without resounding successes.
Related plants:
Spear Thistle (C. vulgare).
Plants of similar appearance:
The presence of a perennial spreading root system and the absence of wings down the stem helps to separate this species from Slender (Carduus pycnocephalus and C. tenuiflorus) and Nodding (Carduus nutans) Thistles. The soft bracts round the flower contrast with the hard spiny bracts of Slender, the only other species with small purple flower heads.
Spear Thistle (Cirsium vulgare) is a biennial with spiny wings extending down the stem.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P94?.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P933.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P28-29. Diagrams.
Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P38-39. Diagrams.
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). 317.1.
Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P157-160. Diagrams. Photo.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P204-208. Diagram. Photos.
Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P204-208. Diagram. Photos.
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.