Malta Star Thistle
Centaurea melitensis
Photographed at Bumble Bee, Yavapai Co., Arizona, USA on 14 June 2008.
ANNUAL: Herbaceous weed of disturbed ground. Plants may grow to over
a meter in height under favorable soil and water conditions thus
producing thousands of seeds.
ARMED. The phyllaries subtending the flower heads terminate in sharp, 10 mm-long
spines. Smaller spines branch out from the base of the central spine.
FLOWERS: Many spikey, bright yellow disc flowers arranged into a compact
head. The phyllaries around the head bear the spines and are usually cob-webby.
Flowers blooming mid to late spring.
LEAVES: Leaves are narrow, almost linear above, and alternate on stem.
Lower leaves may have additional elongate lobes.
RANGE: Malta, of course, is an island in the Mediterranean and this weed
is not native to the Sonoran Desert; its origin is southern Europe.
Accidentally introduced and now invasive in disturbed habitats along washes and
riparian streams across much of the western United States.
FRUIT: Many seeds develope within each head. They are tan-colored with
fine, white bristles at top.