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Centaurea melitensis

Maltese star-thistle

Attracts Pollinators Attracts Butterflies Deer Resistant Drought Tolerant

Overview

Centaurea melitensis, Maltese star-thistle, is a winter annual in the aster family growing 6-40 inches (15-100 cm) tall on rigid, winged, branching stems. It forms a basal rosette of lobed gray-green leaves in winter, then bolts in spring to produce solitary flower heads ringed by stiff, straw-colored spines 0.4-0.6 inch (10-15 mm) long. Each head holds yellow disc florets about 0.3-0.5 inch (8-12 mm) across that mature into wind- and animal-dispersed seed. The taproot lets the plant exploit dry, disturbed ground, and a single plant can set hundreds of seeds. Native to the Mediterranean Basin, it has naturalized widely in California and the western United States, where it colonizes rangeland, roadsides, and open fields. C. melitensis is listed as a noxious or invasive weed in California and several other western states, and dense stands crowd out forage and native annuals. The foliage and seed are linked to a neurological disorder in horses that consume large amounts over time. It completes its life cycle in a single season and dies after seeding, persisting in an area through its long-lived seed bank.

Native Range

Centaurea melitensis is native to the Mediterranean region of southern Europe, North Africa, and the Middle East. It has become naturalized across California, the southwestern United States, South America, and Australia. In North America it is most abundant in California grasslands and foothills.

Suggested Uses

Centaurea melitensis has no horticultural use and is treated as an invasive weed across its naturalized range. In its native Mediterranean habitats it grows among other annuals on open, rocky ground. Land managers target it for control on rangeland and in natural areas.

How to Identify

Look for a spiny annual with winged stems and small yellow flower heads guarded by a collar of slender spines. The basal rosette has lobed, cobwebby gray-green leaves, and the stem leaves run down the stem as narrow wings. Compared with yellow star-thistle (C. solstitialis), its spines are shorter at 0.4-0.6 inch (10-15 mm) and its heads are smaller and more clustered. Crushed foliage has a faint resinous smell.

Appearance

Size & Dimensions

Height6" - 3'4"

Width/Spread6" - 1'6"

Colors

Flower Colors

yellow

Foliage Colors

gray green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~10 weeks

Spring Summer

Flowering runs from late spring through summer, mainly May to July, with stressed plants flowering as early as April. Yellow heads open over several weeks and quickly form seed. By midsummer most plants have dried to brittle, spiny skeletons.

Detailed Descriptions

Foliage Description

Gray-green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 8.0(Neutral)

357912

Soil Types

clay loam sand rocky

Drainagewell drained

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Maltese star-thistle needs no cultivation and grows as a weed in full sun on dry, disturbed soils of almost any texture. It germinates with fall and winter rains, overwinters as a rosette, and flowers as soils dry in spring. The deep taproot makes established plants drought-tolerant and hard to pull once mature. Because it is invasive, it is managed rather than planted: mowing or hand-removal before seed set, combined with competition from perennial cover, reduces stands over time. It tolerates poor, rocky, and alkaline soils and reseeds aggressively where bare ground is available.

Pruning

Mowing or cutting at early flowering, before spines harden and seed forms, limits seed production. Repeated cuts through the season weaken the taproot. Cut material with mature heads can still ripen seed and is removed from the site.