Golden thistle [Scolymus hispanicus L.][Bayer code: none][CDFA list: A] Photographs Map of Distribution

[Back to Index]


SYNONYMS:Spanish salsify, Spanish oyster, scolymus

GENERAL DESCRIPTION:Spiny biennial to perennial with milky sap and yellow flower heads, to 1(2.5) m tall. Golden thistle is primarily a threat to rangeland habitats. Livestock avoid consuming it, and heavy infestations can crowd out desirable forage plants. Introduced from the Mediterranean region as a medicinal herb and root vegetable. See Comparison of spiny-leaved thistles.

SEEDLINGS:Exist as basal rosettes through the first year. Rosette leaves variegated, once-pinnately spiny-lobed, to 30 cm long, with short, fleshy stalks.

MATURE PLANT:Stems erect, robust, highly branched, especially near the top. Foliage typically sparsely covered with hairs, especially midveins on the lower surfaces of leaves. Leaves alternate, dark green, usually with pale green veins and markings, once-pinnately spiny-lobed, with spiny leaf bases that extend down the stems as wings (decurrent). Stem leaves stiff, leathery; basal leaves relatively soft.

ROOTS and UNDERGROUND STRUCTURES:Taproot stout, to 8 cm in diameter and 60 cm long. Taproots remain alive after above ground stems senesce in summer and produce new rosette leaves in fall.

FLOWERS:July. Heads sessile, terminal and lateral, solitary or clustered, 1.5-2(3) cm in diameter, with yellow ligulate flowers. Corollas 5-lobed. Phyllaries in several rows, narrowly lanceolate, spine-tipped, with papery margins, and gradating into leaf-like bracts. Receptacles covered with long, broad, chaff scales that enclose fruits.

FRUITS and SEEDS:Achenes club-shapped, flattened, 3-5 mm long, yellowish-brown. Pappus bristles 2 or 4, rigid, unequal, deciduous.

POSTSENESCENCE CHARACTERISTICS:Flowering stems can remain erect for an extended period or break off at the base with strong winds.

HABITAT:Dry soils of disturbed sites, fields, grassy areas.

DISTRIBUTION:Uncommon. San Francisco Bay region (w Alameda Co.), southeastern Sacramento Valley (nw Solano Co.). To 100 m (330 ft). Previous infestations now eradicated were located in eastern San Mateo and northwestern Santa Clara counties.

PROPAGATION/PHENOLOGY:Reproduces by seed. Seed disperses primarily when stems break off in strong winds and roll along the ground like tumbleweeds, but also with water, in the fur of animals, and by human activity. Seeds germinate throughout fall, winter, and spring.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Manual removal can discourage survival if the root is cut at least 3 inches below ground level.

SIMILAR SPECIES:Unlike golden thistle, smooth and wooly distaff thistles [Carthamus baeticus (Boiss.& Reuter) Nyman, Carthamus lanatus L., respectively] and blessed thistle [Cnicus benedictus L.] lack milky sap, have smooth, wingless stems and flower heads consisting of disk flowers. In addition, distaff thistles are winter annuals and have spiny pinnate-lobed outer phyllaries and fruits with numerous unequal pappus scales. Blessed thistle has leafy heads with smooth-margined outer phyllaries, inner phyllaries with long spiny pinnate-branched tips, and cylindrical, prominently ribbed achenes with crown-like teeth on the apical rim and ~ 20 stiff pappus bristles in 2 series (outer long; inner short). Blessed thistle is a biennial that occurs sporadically in disturbed places, fields, and along roadsides in the North Coast Ranges, Central Valley, Central-western region, South Coast, and western Mojave Desert, to 800 m (2600 ft). Introduced from Europe as a medicinal herb.


Prevention: Golden thistle is a spiny perennial native to the Mediterranean region. Although currently found only in Alameda County, it poses a serious threat to California's range and wildlands. It is classified as a CDFA class A noxious weed. Heavy infestations reduce range quality and carrying capacity. Livestock rarely graze rosettes and completely avoid mature plants due to their spiny nature.
Golden thistle establishes in degraded areas and along fences or waterways where plant skeletons collect after detached stems wind disperse in a tumbleweed manner. Seedlings may emerge from fall to spring. Seeds may also be dispersed in animal hair or fur, vehicles, or other farm equipment. Avoid driving through infestations and prevent livestock from overgrazing around infested areas.

Mechanical: Hand digging isolated plants is difficult, but effective. The stout taproot must be removed to a depth of several centimeters to prevent new shoot emergence. Tillage is effective but generally impractical for infested areas. Seed longevity is unknown and previously infested areas should be monitored for new seedlings for several years.

Biological: There are currently no registered biocontrol agents for golden thistle. Eradication is highly probable due to the small size of known infestations.

Chemical: Picloram has been used previously for golden thistle eradication and provided excellent control. However, picloram is not currently labeled in California. Clopyralid is a selective broadleaf herbicide that controls many other thistles in the Asteraceae family, but has not been tested on golden thistle. Clopyralid is labeled for use on California rangeland, but may injure legumes. The herbicide 2,4-D (2 lb ae/A) has given variable control of golden thistle and subsequent applications will likely be necessary. Dicamba (0.25-2.0 lb ae/A) or triclopyr (0.5 lb ae/A) may be effective, but have not been tested. Dicamba, triclopyr, and 2,4-D may injure or kill other broadleaf plants.

Johnston, J. and Sonder, L. 1970. Golden thistle eradication in Alameda County
Eradication of noxious weeds in California. California Weed Conference Proceedings. 22:75-76.
Parsons, W. T. and Cuthbertson, E. G. 1992. Noxious weeds of Australia. Melbourne: Inkata Press.
Back to top