L.

tocolote, Maltese star thistle, Napa star thistle, Malta starthistle

none known

0

11

CalEPPC List B,CDFA nl

John D. Gerlach Jr.,Joseph M. DiTomaso

In California, tocolote (Centaurea
melitensis) grows as a winter annual, producing one to several solitary or
clustered, spiny, yellow-flowered heads during spring and early summer. The
pre-bolting vegetative characteristics of this species are similar to those of
yellow starthistle. Bolting occurs during early spring. The stem leaves extend
downward, giving the stems a winged appearance. Flowerheads are generally
produced from April through June (approximately four to six weeks before yellow
starthistle begins flowering). Flowering plants range from two to thirty-six
inches in height and may change from green to bluish green as they senesce. The
main phyllaries are pinnately spined with an apical, needle-like spine and a
few, much smaller, lateral spinelets. The apical spine bears a characteristic
pair of spinelets approximately one-eighth inchåÊ from its base. The heads
produce only one type of fruit or achene, which is usually light brown with
faint tan stripes and always bears a white pappus.

Tocolote is widely distributed in California,
but the largest populations are found in central-western and southwestern
regions of the state (Hickman 1993). Scattered small to medium-sized populations
occur in the San Francisco Bay Area, North Coast Ranges, and Sierra Nevada
foothills.

Tocolote was brought to California during the
Spanish mission period. The earliest record of its occurrence was seed found in
adobe bricks of a building constructed in 1797 in San Fernando (Hendry 1931). It
appears to have been a contaminant in wheat, barley, and oat seed and was widely
distributed in dry-farmed grain fields. In one instance its seed was found
embedded in an oat floret (Stanton and Boerner 1936). Seed is transported by
humans, animals, or wind, similar to starthistle (Gerlach unpubl.
data).

Dense infestations of tocolote displace
native plants and animals, threatening natural ecosystems and nature reserves.
It significantly reduces seed production of the endangered plant, Acanthomintha
ilicifolia (Bauder unpubl. data). Long-term ingestion by horses causes a chewing
disease, a lethal lesion of the nigropallidal region of the brain (Kingsbury
1964).

Tocolote generally flowers from April through June. Inflorescences can produce 1 to 100 heads with 1 to 60 seeds per head (Gerlach unpubl. data). Nothing is known about its pollination biology. Wild oat (Avena fatua) litter has been implicated as producing allelopathic compounds that significantly reduce seed germination (Tinnin and Muller 1972). A study of European plants found that young seedlings are resistant to the effects of fall drought (Espigares and Peco 1995). Little is known about the biology of tocolote. Seeds germinate after fall rains, bolting occurs in early spring, and plants flower from spring to early summer.

(click on photos to view larger image)

Centaurea solstitialis on left; C. melitensis on right

Little work has focused on the control of
tocolote. However, it is likely that the strategies used to successfully control
yellow starthistle (Centaurea solstitalis) will also provide effective control
of this species. A possible difference in control would be methods for
biological control.

Insects and fungi: No specific biological
control agents have been released to control tocolote, and none of the agents
introduced to control yellow starthistle have reproduced on tocolote. In a field
test of alternate plant hosts, the weevil Bangasternus orientalis,
which was introduced to control starthistle, did not reproduce on tocolote
(Woods et al. 1995). While no biological control agents have been released to
control this species, a small beetle inadvertently introduced into California
has been found to destroy mature seeds in the seedhead (Pitcairn and Gerlach
unpubl. data). This beetle, Lasioderma haemorrhoidale, was first collected in
Santa Clara and Fresno counties during 1981, 1982, and 1983 (White 1990). In
1997 the beetle was found on Centaurea melitensis seed heads collected in San
Diego and Colusa counties. The home range of the beetle is the entire
Mediterranean region, and it appears to specialize on species in the thistle
tribe (White 1990).