**Sonchus asper (L.) Hill (Asteraceae)**

**Prickly Sow Thistle, Spiny Milk Thistle**

**Description**. Annual, sometimes biennial, 1-10(15) dm tall, erect,
herbaceous, generally glabrous, from a stout taproot. Central stem
somewhat succulent, stout, angled, glabrous, the lateral stems erect to
ascending. Leaves alternate, 5-30 cm long, oblanceolate, auriculate, the
auricles rounded, lower leaves slightly to deeply lobed, the deeper
lobes ovate, spiny-toothed, the uppermost leaves ovate, often simple
with spiny-toothed margins. Heads ligulate (all corollas bilateral and
bisexual), 1.5-2.5 cm wide, hemispherical, stalked, solitary or in small
corymbose terminal clusters of 2-7. Phyllaries in several unequal
series, oblong to lanceolate, becoming thick with age, the outer ones
shorter than the inner. Flowers bisexual, corollas ligulate, yellow, the
ligules shorter than the tube. Achenes 2-3 mm long, ellipsoid to
obovoid, compressed, usually 3-4-ribbed, usually smooth, the margins
wing-like; pappus 6-9 mm long, soft, capillary, falling in a ring.
Flowering in California from March to September (Barkley 1986, Boulos
1976, Clapham et al. 1962, Cronquist 1994, Ferris 1960, Gleason and
Cronquist 1991, Munz 1959, Stebbins 1993).

The closely related species, *S. oleraceus* L. (common or annual sow
thistle) differs primarily by having sharply acute leaf auricles, and
achenes with 3-5 ribs that are evidently rugose. *Sonchus tenerrimus* L.
has acute auricles, ligules much longer than the corolla tube, and the
somewhat terete, transversely rugose achenes have 1-3 ribs. Both species
have unwinged achenes.

**Geographic distribution**. Natives of northern Europe, western Asia,
and northern Africa, both *Sonchus asper* and *S. oleraceus* are
introduced and widespread throughout temperate regions of all 6 arable
continents, Hawaii, and New Zealand (Arnold and De Wet 1993, Boulos
1976, Chapman 1991, Cronquist 1994, Wagner et al. 1990, Webb et al.
1988).

Both *Sonchus asper* and *S. oleraceus* were reported from California as
early as 1865 by Brewer et al. (1876) and Bolander (1870), but *Sonchus
asper* was probably in California prior to the 1770's (Hendry and Bellue
1925, Robbins 1940). Both species are present on all four northern
Channel Islands; *Sonchus oleraceus* is also known from Santa Barbara
Island (Junak et al. 1997). Both species have been reported from most
California counties (Anonymous 1998, Stebbins 1993).

**Reproductive and vegetative biology**. We found no literature specific
to the breeding system of *Sonchus asper* and near relatives. However,
this species has bisexual flowers and presumably is pollinated by small
insects, as are other members of the Lactuceae (Richards 1986, Proctor
et al. 1996). Like other Asteraceae with a capillary pappus and small
light seeds, *Sonchus* presumably has a relatively high level of
dispersability (Anderson 1992, Sheldon and Burrows 1973). Seeds of *S.
oleraceus* germinate readily under either light or dark conditions,
generally at temperatures ranging from 7 degrees C to above 35 degrees C
(Anderson 1968).

**Ecological distribution**. In both natural and naturalized geographic
ranges, *Sonchus asper* and *S. oleraceus* occur on disturbed sites of
waste areas, orchards, roadsides, open sites in grasslands, and
abandoned fields (Boulos 1976, Chapman 1991, Cronquist 1994, Gleason and
Cronquist 1991, Holm et al. 1977, Webb et al. 1988). *Sonchus asper* was
a common invasive in Australian shrublands (Purdie 1977, Purdey and
Slatyer 1976). Trabaud (1990) reported *Sonchus oleraceus* as a common
invasive of burned shrubland in France.

**Weed status.** *Sonchus asper* is not considered a noxious weed in
agricultural or horticultural practice, at least at a global level (not
listed by Holm et al. 1977). However, *Sonchus oleraceus* is treated as
a noxious weed by Holm et al. (1977). Both species are listed as weeds
in the United States in Lorenzi and Jeffery (1987), but they are not
considered noxious by the State Dept. of Food and Agriculture (Anonymous
1996).

**Microbial and insect pathogens**. Whiteflies (*Bemisia argentifolii*)
have been reported to occur on *Sonchus oleraceus* (Summers et al.
1996). No other literature was found that reported *Sonchus asper* or
*S. oleracea* as a host of detrimental fungal or insect pathogens.

**Herbicide control**. Lorenzi and Jeffery (1987) recommended the use of
2,4-D prior to bolting in grassland infestations. No other literature
was found that reported herbicide treatment.

**Literature Cited**

Anderson, R. 1968. Germination and establishment of weeds for
experimental purposes. Weed Science Society of America, University of
Illinois, Urbana. 236 pp.

Anderson, M. 1992. An analysis of variability in seed settling
velocities of

several wind-dispersed Asteraceae. American Journal of Botany. 79:
1087-1091.

Anonymous. 1996. Exotic pest plants of greatest ecological concern in
California as of August 1996. California Exotic Pest Plant Council. 8
pp.

Anonymous. 1998. California county flora database version 2, Santa
Barbara Botanic Garden and USDA National Plants Data Center, Santa
Barbara and New Orleans. URL = plants.usda.gov

Arnold, T. and B. de Wet. 1993. Memoir 62. Plants of southern Africa:
names and distribution. National Botanical Institute, Pretoria. 825 pp.

Barkley, T. 1986. Asteraceae. pp. 838-1021. In Great Plains Flora
Association. Flora of the Great Plains. University of Kansas Press,
Lawrence. 1402 pp.

Bolander, H. 1870. A catalog of plants growing in the vicinity of San
Francisco. A. Roman and Co., San Francisco, California. 43 pp.

Boulos, L.. 1976. *Sonchus* pp. 327-328. In Tutin et al. (eds). Flora
Europaea. Plantaginaceae to Compositae. Cambridge University Press,
Cambridge. 505 pp.

Brewer, W., S. Watson, and A. Gray. 1876. Geological Survey of
California. Volume 1. John Wilson, University Press, Cambridge,
Massachusetts. 622 pp.

Chapman, A. 1991. Australian plant name index. A-C. Australian
Government Publishing Service, Canberra. 897 pp.

Clapham, A., T. Tutin, and E. Warburg. 1962. Flora of the British Isles.
Cambridge University Press, Cambridge. 1269 pp.

Cronquist, A. 1994. Intermountain Flora. Volume 5. Asterales. New York
Botanical Garden, Bronx. 496 pp.

Ferris, R. 1960. Illustrated flora of the Pacific states. Volume 4.
Bignoniaceae to Compositae. Stanford University Press, Stanford,
California. 732 pp.

Gleason, H. and A. Cronquist. 1991. Manual of the vascular plants of
northeastern United States and Adjacent Canada. 2nd edition. New York
Botanic Garden, Bronx. 910 pp.

Hendry, G, and M. Bellue. 1925. The plant content of adobe bricks.
California Historical Society Quarterly 4: 361-373.

Holm, L., D. Plucknett, J. Pancho, and J. Herberger. 1977. The world's
worst weeds: distribution and ecology. University Press of Hawaii,
Honolulu. 609 pp.

Junak, S., S. Chaney, R. Philbrick, and R. Clark. 1997. A checklist of
vascular plants of Channel Islands National Park. Southwest Parks and
Monuments Association, Tucson, AZ. 43 pp.

Lorenzi, H. and L. Jeffery. 1987. Weeds of the United States and their
control. Van Nostrand Company, New York. 355 pp.

Munz, P. 1959. A flora of California. University of California Press,
Berkeley. 1681 pp.

Proctor, M., P. Yeo, and A. Lack. 1996. The Natural history of
pollination. Timber Press, Portland, Oregon. 479 pp.

Purdie, R. 1977. Early stages of regeneration after burning in dry
sclerophyll vegetation. II. Regeneration by seed germination. Australian
Journal of Botany. 25: 35-46.

Purdie, R., and R. Slatyer. 1976. Vegetation succession after fire in
sclerophyll woodland communities in south-eastern Australia. Australian
Journal of Ecology. 1: 223-236.

Richards, A. 1986. Plant breeding systems. Cambridge University Press,
Cambridge, Great Britain. 529 pp.

Robbins, W. 1940. Alien plants growing without cultivation in
California. Agricultural Experiment Station. Bulletin 637. University of
California, Berkeley. 128 pp.

Sheldon, J. and F. Burrows. 1973. The dispersal effectiveness of the
achene-pappus units of selected Compositae in steady winds with
convection. New Phytologist 72: 665-675.

Stebbins, G.. 1993. Sonchus. p. 344. In Hickman, J. (ed.). The Jepson
Manual: higher plants of California. University of California Press,
Berkeley. 1400 pp.

Summers, C., A. Newton, and D. Estrada. 1996. Intraplant and interplant
movement of *Bemisia argentifolii* (Homoptera: Aleyrodidae) crawlers.
Environmental Entomology. 25: 1360-1364.

Trabaud, L. 1990. Fire as an agent of plant invasion. A case study in
the French Mediterranean vegetation. pp. 417-437. In Di Castri, F., A.
Hansen, and M. Debussche. Biological invasions in Europe and the
Mediterranean Basin. Dordrecht: Kluwer.

Wagner, W., D. Herbst, and S. Sohmer. 1990. Manual of the flowering
plants of Hawaii. 1853 pp.

Webb, C., W. Sykes, and P. Garnock-Jones. 1988. Flora of New Zealand.
Volume 4. Naturalized pteridophytes, gymnosperms, dicotyledons.
Department of Scientific and Industrial Research, Christchurch. 1365 pp.