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Centaurea melitensis

Scientific Name: Centaurea melitensis
Common Names: Tocalote,Maltese star thistle or centaury; Napa thistle; croix de Malte

Line Drawing:

Morphological Description:
flower head has disk flowers only, and lacks the strap-shaped flowers
starts flowering mid-March to mid-April
simple (lobed or unlobed but not separated into leaflets)
Alternate leaf arrangement – one leaf per node along the stem
leaves grow at base of plant

Habitat & Basic Biology (life history, dispersal abilities):
Open disturbed sites, open hillsides, grassland, rangeland, open woodlands, fields, pastures, roadsides, waste places
Reproduces only by seed

Functional traits (photosynthetic rates, phenology, etc.):
Flowering: (Oct.)–Dec.–Feb.
Fruiting: Dec.–May.

Distribution (geographic range):

It is found to be invasive along the western coast and elsewhere in the United States

Control Methods:
Biological Control: Six biological control insects have been released in the United States. Of these, three (B. orientalis, U. sirunaseva and E. villosus) are widespread.

Chemical Control:Application of the systemic herbicides clopyralid or picloram between December and April seems to be the most effective. Application during the winter encourages the growth of other, more desirable, plants.

Mechanical Control: Mowing is effective during the early flowering stage.

Grazing: Sheep, goats, and cattle can graze on yellow starthistle in early spring, before spines develop.

Evolution (of traits in novel range):
invasive populations are genetically differentiated from native ones for several life history traits and their plasticities
the niche of invasive plants has shifted from those of native plants
overall phenotypic plasticity

Performance of invader in CA (interactions with species native to S. CA):
Phenotypic plasticity and differentiation in fitness-related traits after introduction contributes  increased performance

Natural enemies:
Insects in the orders of Coleoptera, Lepidoptera, and Diptera

List of References:
Calflora: Information on California plants for education, research and conservation, with data contributed by public and private institutions and individuals, including the Consortium of Calif. Herbaria. [web application]. 2014. Berkeley, California: The Calflora Database [a non-profit organization]. Available:   (Accessed: Jun 09, 2014).

“Centaurea Melitensis.” Texas Invasive Plant and Pest Council, 24 Nov. 2008. Web. 9 June 2014. <>.
The Texas Invasive Plant and Pest council provides a comprehensive plant database of information regarding invasive species.

“Centaurea Melitensis L.” Centaurea Melitensis. GoBotany, n.d. Web. 09 June 2014. <>.
GoBotany is an organization supported by the National Science Foundation and New England Wildflower Society.

DiTomaso, J.M., G.B. Kyser et al. 2013. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center, University of California. 544 pp.
This weed report is an excerpt from the book Weed Control in Natural Areas in the Western United States.

Moroney, Jolene Rene. “Electronic Thesis and Dissertations.” EScholarship. University of California, 2012. Web. 09 June 2014. <>.
This paper examines the ecological and evolutionary factors that produce invasive populations.

Moroney, Jolene Rene. “Result Filters.” National Center for Biotechnology Information. U.S. National Library of Medicine, 8 Oct. 2013. Web. 09 June 2014. <>.
Moroney and associates compared several fitness-related traits and the phenotypic plasticity of those traits under four levels of nutrients among native and invasive populations of Centaurea melitensis.

Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. 1988: Flora of New Zealand. Vol. IV. Naturalised Pteridophytes, Gymnosperms, Dicotyledons. Botany Division, D.S.I.R., Christchurch, New Zealand.
Flora of New Zealand provides a dynamic and updated database of various flora.