Yellow starthistle [Centaurea
solstitialis L][CENSO][CalEPPC: A1][CDFA list: C] Photographs
Malta starthistle or
Tocalote [Centaurea melitensis L.][CENME][CalEPPC: B] Photographs
[Centaurea sulphurea Willd.][CDFA list: B] Photographs
Map of Distribution
DESCRIPTION: Noxious erect winter annuals (sometimes
biennials) with spiny yellow-flowered heads, mostly to
1 m tall. Refer to the table Comparison of yellow-flowered
starthistles for a quick review of important differences.
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oblong to spatulate, base wedge-shaped, tip +/- squared. First
few leaves typically oblanceolate. Subsequent rosette leaves oblanceolate,
entire to pinnate-lobed. Terminal lobes largest. Later rosette
leaves to 15 cm long. Hair characteristics are visible with 10-14x
stiff, openly branched from near or above the base or sometimes
not branched in very small plants. Stem leaves alternate, mostly
linear or +/- narrowly oblong to oblanceolate. Margins
smooth, toothed, or wavy. Leaf bases extend down the stems (decurrent)
and give stems a winged appearance. Rosette leaves typically withered
by flowering time.
and UNDERGROUND STRUCTURES:
FLOWERS: Heads ovoid,
spiny, solitary on stem tips, consist of numerous yellow disk
flowers. Heads sometimes closely 2-3-clustered in Malta starthistle.
Vigorous individuals of Malta and yellow starthistle
may develop flower heads in branch axils. Phyllaries palmately
spined, with one long central spine and 2 or more pairs of short
lateral spines. Insect-pollinated.
and SEEDS: Achenes (seeds) +/- barrel-shaped, +/- compressed,
laterally notched at the base. Pappus bristles slender, stiff,
CHARACTERISTICS: Stems with old flower heads turn gray-brown and
can remain intact for over a year.
HABITAT: Open, disturbed
sites, grasslands, rangeland, open woodlands, fields, pastures,
roadsides, waste places. Yellow and Malta starthistle
also occur in cultivated fields.
by seed. Seeds fall near the parent plant or are dispersed
to short distances with wind and to greater distances with human
activities, animals, water, and soil movement. Most seeds germinate
after the first fall rains. Plants exist as basal rosettes through
winter and early spring until flowering stems develop in late
spring or early summer.
FAVORING/DISCOURAGING SURVIVAL: Monitoring and spot eradication of plants when
they are discovered can prevent the spread of starthistles.
Unlike yellow, Malta, and Sicilian starthistle, purple
starthistle [Centaurea calcitrapa L.] and Iberian starthistle
[Centaurea iberica Spreng.] have purple flowers, upper stem
leaves mostly pinnate-divided, and straw-colored spines in the
center of the rosettes.
A very large compendium of biology, ecology and control information has been
compiled by Dr. Joseph DiTomaso at the University of California Davis. The information
can be accessed via the world wide web at the following address: http://wric.ucdavis.edu/yst/index.html
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