Centaurea melitensis, Maltese Star-thistle
Scientific Name: Centaurea melitensis
Common Name: Maltese Star-thistle
Also called: Malta Thistle, Maltese Star Thistle, Malta Starthistle, Maltese Star-thistle, Napa Thistle, Spotted Knapweed, Tocalote, Tocolote (Spanish: Cardo)
Family: Asteraceae, Sunflower Family
Synonyms: ( )
Status: Introduced; naturalized, European.
Duration: Annual or biennial.
Size: 3 feet more or less.
Growth Form: Forb/herb; stems erect, stiff, mostly 1 stem, large plants openly branched, stems winged; gray-hairy, resin-dotted.
Leaves: Green, grayish green; alternate; decurrent on the stem; fine hairs, thinly tomentose, scabrous and puberulent basal rosette, pinnately divided, oblong or oblanceolate; margins entire to lobed, lower leaves usually dried by bloom period; upper leaves variable, linear or elliptical.
Flower Color: Yellow; 1 to many spiny discoid flowers, peduncled or sessile in axils; corollas ovoid, yellow and somewhat cobwebby or becoming glabrous, straw colored; phyllaries spine tipped, central spine longest, slender and recurved; terminal spine or prickle of the phyllary normally purplish toward the base, less than 1 cm long; fruit is an achene, fine tan or white pappus bristles.
Flowering Season: April or May to July.
Elevation: Up to 4,500 feet more or less.
Habitat Preferences: Various habitats, lower and upper deserts, pinyon-juniper communities, chaparral and grasslands, disturbed areas, roadsides, agriculture areas and open woodland.
Recorded Range: Primarily a western invasive species in North America quickly spreading east of the Mississippi River extending currently to Massachusetts. Invasive also in Hawaii. In central, south northwest and northeast Arizona.
North America & US County Distribution Map for Centaurea melitensis.
U.S. Weed Information: Centaurea melitensis can be weedy or invasive as noted by the USDA, Natural Resources Conservation Service. It is considered a weed by the following; Cal-IPC, California Invasive Plant Council.
Plants included here may become weedy or invasive.
Invasive/Noxious Weed Information: Centaurea melitensis is listed by the USDA, Natural Resources Conservation Service as a Noxious Weed in: Nevada, Malta thistle is a Noxious weed and in New Mexico, Malta Starthistle is a Class B noxious weed.
Plants included here are invasive or noxious.
Wetland Indicator: No data available.
Threatened/Endangered Information: No data available.
Genus Information: In North America there are 34 species and 38 accepted taxa overall for Centaurea. Worldwide, The Plant List includes 734 accepted species names and a further 1,150 scientific names of infraspecific rank for the genus Centaurea. Members of the genus Centaurea are commonly known as Knapweeds.
In the Southwestern United States: Arizona and New Mexico each have 8 species of Centaurea, California has 17 species, Nevada has 5 species, Texas has 4 species, Utah has 10 species. All data is approximate and subject to taxonomic changes.
Comments: Maltese Star-thistle is an aggressive weed which was introduced to North America (California) in the 18th century. It is a native of the Mediterranean region of Europe and Africa. It continues to spread across North America where it is already listed as a noxious weed in many states. The numerous common names of a plant is often a clue as to its economic significant or importance across its range, either positive or notoriously; such is the case for the Maltese Star-thistle.
Special Value to Native Bees; European Honey Bees (Apis mellifera) are important pollinators of Maltese Star-thistle. Bumblebees (Bombus) are also important floral visitors.
Also see in Southwest Desert Flora; Yellow Star-thistle, Centaurea solstitialis.
The species epithet melitensis is derived from the Latin word "Melita" (adj Maltese) meaning Malta a reference to the the Mediterranean region of Europe and Africa where it is native.
Maltese Thistle has been used as a kidney aid by southwestern United States indigenous peoples.
See complete listing of ethno-botanical uses at Native American Ethnobotany, University of Michigan, Dearborn.