Sonchus is the Greco-Latin name of the Sow Thistle.
Rough Sowthistle
Other names:
Prickly Sowthistle
Spiny Sowthistle
Rough Milk Thistle
Summary:
Rough Sowthistle is an erect, branched annual or biennial herb about 1 m tall with hollow stems which have a milky sap. The basal leaves are up to 30 cm long, form a rosette and are somewhat leathery and toothed with the teeth sometimes prickly. The stem leaves are somewhat smaller and stem clasping. The yellow dandelion-like flower heads are clustered, each about 2 cm in diameter, with all the florets having a radiating petal-like blade. The tiny fruits are short and flattened, topped by a tuft of fine soft bristles. Native to Europe, Asia and northern Africa, they are common weeds of pasture and waste land, but also invade bushland, particularly in damp areas. It flowers for much of the year but mainly in spring and early summer.
Description:
Cotyledons:
Two. Oval with a rounded tip, 12 to 18 mm long with a very short merging petiole. Base tapered. Hairless, or the upper surface may carry a few white multi-cellular hairs. The seedling has a very short hypocotyl and no epicotyl.
First Leaves:
Arise singly, the first being oval, with a rounded tip, 12 to 18 mm long overall with a petiole approximately 5 mm long. A few white multi-cellular hairs may occur on the upper surface, and the margin is slightly toothed and spined. Later leaves are more lobed and usually hairless.
Leaves:
Develops as a rosette about 250 mm in diameter. Exudes a sticky white sap when damaged.
Petiole - None.
Blade - Dark green, stiff, leathery, egg shaped and shallowly lobed or toothed, rarely deeply lobed, 200 mm long by 50 mm wide, prickly, sometimes glossy and usually are hairless. Broad basal lobes rounded with prickly teeth and bent downwards. End lobe is not wider than the upper side lobes. Hairless.
Stem leaves - Alternate, stalkless and clasping, but are not continued as wings down the stem. The upper leaves carry a reduced number of lobes or no lobes at all, and are bent back. The leaves are hairless and the upper surface is shiny. Broad basal lobes rounded and bent downwards against the stem.
Stems:
Erect, up to 1500 mm tall, circular in cross section, shallow fluting, hollow, waxy bloom, and has dark longitudinal striations. Branched especially towards the top. The stems are hairless or carry a few scattered purplish glandular hairs towards the top. When cut the plant exudes a milky latex.
Flower head:
Several head in a corymb at the ends of stems on stalks(peduncles) usually with dark glandular hairs. Heads 10 to 15 mm in diameter by 9-25 mm long.
Flowers:
Golden yellow, thistle type. with ligulate florets,
Bracts -
Florets - Tubular, all with 'petals'(ligules), tubes longer than 'petals'
'Petals' - Pale yellow.
Stamens -
Anthers -
Fruit:
Brown, oval, flattened achene with 3-5 obvious, smooth, lengthwise ribs on each face, otherwise smooth, never crosswise wrinkled, 2.5-3 mm long by 1.5 mm wide including the 2 wings which are usually hairy. Pappus of many, very fine, silky bristles.
Seeds:
Enclosed in the achene.
Roots:
Taproot.
Key Characters:
Terminal lobe of leaves not wider than upper laterals, margins spinose-ciliate, base of leaf broadened into rounded appressed auricles.
Stems leafy.
Sap milky.
Inflorescence branched.
Florets all ligulate.
Receptacle naked.
Achenes ovate-oblong to elliptic in outline, narrowed towards both ends, compressed, obtuse, ribbed lengthwise, glabrous, not beaked, margin narrowly winged, faces with 3-5 prominent ribs which are never raised to form small wings.
Pappus of numerous silky bristles intermixed with fine down like barbed hairs.
From J.M. Black, N.T. Burbidge and N.S. Lander.
Biology:
Life cycle:
Annual or biennial. Seeds germination from autumn to spring. They grow mainly through the winter and usually die after flowering.
Physiology:
Reproduction:
By seed.
Flowering times:
Mainly spring in wester NSW.
August to November in Perth.
Throughout the year in WA.
Seed Biology and Germination:
Vegetative Propagules:
None.
Hybrids:
Intermediate forms between Common Sowthistle (Sonchus oleraceus) and Rough Sowthistle (Sonchus asper) may occur.
Allelopathy:
Population Dynamics and Dispersal:
Seed is mainly spread by wind.
Since it is palatable in the young stages it does not normally survive in pasture.
Origin and History:
Europe.
Distribution:
ACT, NSW, SA, TAS, VIC, WA.
Prickly sow Thistle occurs in all parts of Tasmania.
Habitats:
Climate:
Temperate. Mediterranean.
Soil:
Most soil types.
Most abundant on fertile damp soils.
Plant Associations:
Most communities.
Significance:
Beneficial:
Fodder.
Detrimental:
Weed of roadsides, gardens, fallows, cultivated areas, many crops and disturbed areas.
Toxicity:
Plants affected by aphids may cause photo sensitisation in cattle.
Legislation:
None.
Management and Control:
Establish competitive pastures and graze.
Thresholds:
Eradication strategies:
Manually remove isolated plants or graze the area to prevent seed set for several years.
Single plants may be sprayed with 50 mL glyphosate(450g/L) in 10 L water or wiped with a mixture 1 L glyphosate(450g/L) in 2 L water at any time before budding.
Spray small areas with a mixture of 100 mL of Tordon®75-D plus 25 mL wetting agent in 10 L of water in June each year. This will kill growing plants and leave a soil residue to control seedlings.
In bushland situations 4 L/ha 2,4-DB(400g/L) or 80 mL 2,4-DB(400g/L) plus 25 mL wetting agent in 10 L of water for hand spraying will provide reasonably selective control when applied in June. A repeat application may be necessary in late spring if a spring germination occurs.
Herbicide resistance:
Biological Control:
Related plants:
Clammy Sowthistle (Sonchus tenerrimus) has wrinkled achenes that taper at the base.
Common Sowthistle (Sonchus oleraceus) has roughened ribs on the achene, is less robust, with softer leaves which are not prickly-toothed. The two species are often difficult to tell apart and occasional hybrids have been found.
Corn Sowthistle (Sonchus arvensis)
Native Sowthistle (Sonchus hydrophilus) has seeds(achenes) with hairy ribs has longer narrower leaves which are wavy or shallowly lobed rather than prickly-toothed.
Plants of similar appearance:
In the later stages of growth Rough Sow Thistle can be distinguished from Sow Thistle by the leaf shape and the curled leaf base. The leaves are also harder in texture, pricklier and glossier. In the early seedling stage the two thistles are, for all practical purposes, indistinguishable. In the rosette Sow Thistle tends to have rounder leaves and a long narrow petiole-like leaf base, while Rough Sow Thistle leaves have a tapering, more or less sessile base.
Capeweed (Arctotheca calendula) has a light underside and darker upper surface on the leaf.
Dandelion (Taraxacum officinale)
Flatweed (Hypochoeris radicata)
Fleabane (Conyza spp.)
Hawkbit(Leontodon taraxacoides)
Indian Hedge Mustard (Sisymbrium orientale)
Ox tongue (Helminthotheca echioides)
Prickly Lettuce (Lactuca serriola)
Rapistrum (Rapistrum rugosum)
Slender Thistle (Carduus spp.)
Smooth Catsear (Hypochoeris glabra)
Skeleton Weed (Chondrilla juncea) has backward pointing leaf lobes.
Sow Thistle (Sonchus oleracea) has lighter green, softer, more lobed leaves and wrinkled achenes.
Wild Radish (Raphanus raphanistrum)
Wild Turnip (Brassica tournefortii)
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P116-117. Photo.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P943.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P398.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P717. Photo.
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P106-107. Photo.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P34-35. 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). #1145.2.
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). P708.