Perennial Sow Thistle
Sonchus arvensis L.
Family: Asteraceae
Description and life cycle
Perennial sow-thistle is a herbaceous perennial that reproduces from seed and from an extensive
creeping root system. The roots penetrate down to 3 m, but, most of the system is within the
top 5 - 15 cm of soil. Roots break easily and regenerate from buds. Hollow, erect stems can
reach 0.6 - 1.5 m tall and contain a bitter, milky juice. Stems are non-branching until near
the top. A variety of leaf shapes and sizes are arranged alternately along the stem - upper
leaves are clasping while the lower leaves narrow to a winged stalk. All leaves have deep lobes
and weak prickles along their margins. Bright yellow blossoms appear in June and continue into
September. At peak bloom, each flower can reach 3.8 cm across. A single plant can have as many
as 20 flower heads, but, few come into flower at the same time. It is a prolific seed producer
with about 10,000 seeds produced per flowering stem. The ribbed seeds have attached pappus
which assists with their distribution.
British Columbia Biological control agents
References
British Columbia Ministry of Agriculture and Food. No date. Perennial sow thistle (Sonchus
arvensis L.). agdex 640. Govt. of BC.
Cranston, R., D. Ralph and B. Wikeem. 2005. Field guide to noxious and other selected weeds
of British Columbia. Gov. of BC. 94 p.
Frankton, C. and G. A. Mulligan. 1987. Weeds of Canada.
Parish, R., R. Coupe and D. Lloyd. 1996. Plants of southern interior British Columbia.
Peschken, D. P. 1982. Host specificity and biology of Cystiphora sonchi [Dip: Cecidomyiidae],
a candidate for the biological control of Sonchus species. Entomophaga, 27: (4): 405-416.
Whitson, T. D. (editor), L. C. Burrill, St. A. Dewey, D. W. Cudney, B. E. Nelson, R. D.
Lee and R. Parker. 1992. Weeds of the west. Western Soc. Weed Sci. and Western U. S. Land Grant
Univer., Cooperative Extension Serv.
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