Golden thistle [Scolymus
hispanicus L.][Bayer code: none][CDFA list: A] Photographs
Map of Distribution
SYNONYMS:Spanish salsify, Spanish oyster, scolymus
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
SEEDLINGS:Exist as basal rosettes through the first year. Rosette leaves
variegated, once-pinnately spiny-lobed, to 30 cm long, with short, fleshy
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.
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.
and SEEDS:Achenes club-shapped, flattened,
3-5 mm long, yellowish-brown. Pappus bristles 2 or 4, rigid,
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
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.
FAVORING/DISCOURAGING SURVIVAL:Manual removal
can discourage survival if the root is cut at least 3 inches below ground
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
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.