Centaurea melitensis
(Maltese starthistle)

Preferred Common Name

• Maltese starthistle

Other Scientific Names

• Calcitrapa patibilcensis Kunth, 1818

International Common Names

• English: Malta starthistle; Maltese cockspur; Maltese star centaury; Maltese star-thistle; Maltese thistle; Napa starthistle; Napa thistle

Local Common Names

• Brazil: centáurea-estrela-de-Malta
• France: coix de Malte
• Germany: Malteser Flockenblume
• Spain: cardo escarolado; yerba de cristo
• USA: tocalote; tocolote

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Asterales
•                         Family: Asteraceae
•                             Genus: Centaurea
•                                 Species: Centaurea melitensis

The synonym Calcitrapa patibilcensis Kunth (published in 1818) was used in a checklist prepared by Hind and Jeffrey (2001). It is not in common use. Centaurea melitensis is the commonly accepted name.

Adapted primarily from Keil and Ochsmann (2006) and DiTomaso and Healy (2007):

Erect plants 10-100 cm tall, herbage grey-green loosely tomentose and villous with jointed multicellular hairs, sometimes minutely scabrous. Leaves dotted with minute resinous glands. Stems single or several with few to many distal branches. Basal and proximal cauline leaves petiolate or tapering to the base, usually absent by anthesis, blades oblong to oblanceolate, 2-15 cm, margins entire to dentate or pinnately lobed. Cauline leaves long, decurrent, forming wings up to 3 mm wide down the stems, blades linear to oblong or oblanceolate, 1-5 cm long, margins entire or dentate. Young leaves sometimes densely covered with fine, cottony hairs, which become sparse with age and no longer hide the stiff hairs and resinous dots. Heads round to ovoid, solitary or in close corymbiform clusters of 2-3 at the tips of stems, sometimes clustered in distal axils, sessile or pedunculate; all disc flowers. Corollas yellow, typically 10-12 mm long. Involucres 8-15 mm, loosely cobwebby-tomentose or becoming glabrous. Central spine of principal phyllaries 5-12 mm long, slender, often purple to brown tinged, with lateral spines in 3 to 4 pairs, the upper pair near the middle of the central spine. Inner phyllary appendages entire, acute or spine-tipped. Three types of capitula are produced: cross-pollinating heads with fully expanded flowers, and two cleistogamous (self-pollinating) types, one with yellow flowers only partially protruding and one without exserted corollas. Three types of achenes are produced, with the variation linked to capitulum type: initial cleistogamous capitula produce thick achenes bearing a short pappus; in final cleistogamous capitula achenes are small with a short pappus; and chasmogamous (outcrossing) capitula produce small achenes with a longer pappus (Porras and Muñoz, 2000). Most achenes are 2-3 mm long, finely pubescent, greyish to tan, usually with slightly darker stripes. The base is deeply notched, narrow, hook-like. Pappus bristles are pale tan, 1-3 mm long.

Seedling identification: Cotyledons oblong to spatulate, base wedge-shaped, tip truncate to slightly rounded, glabrous. First few true leaves typically oblanceolate. Later rosette leaves entire to deeply lobed, nearly to the midvein, lobes usually rounded, including the terminal one. Upper and lower surfaces evenly covered with stiff, thick hairs and resinous glands. Fine, cottony hairs dense on young leaves becoming sparse on older leaves (DiTomaso and Healy, 2007).

C. melitensis was widely distributed throughout the 1700s and 1800s, during the period of worldwide colonization by Spain and Portugal; its seeds were carried in the soil used as ship ballast, lodged in the wool of sheep, and as a contaminant of cereal grains, either in seed or straw (Roché and Talbott, 1986). It was probably introduced in California, USA, in the late 1700s during the Spanish missionary period (Spira and Wagner, 1983; DiTomaso and Healy, 2007). It reached South America, Hawaii, Australia and New Zealand during the same era. It failed to establish in northern and eastern US states, despite numerous introductions. In California, C. melitensis has been more invasive in the west-central and south-western regions, as well as across southern Arizona, New Mexico and western Texas. It forms the dominant vegetation in some California inland valley and foothill annual grasslands (Borchert and Jain, 1978).

Soil drainage

• free

Soil texture

• light
• medium

Special soil tolerances

• infertile
• shallow

Natural Dispersal (Non-Biotic)

Most seeds fall near the parent plant or is dispersed over short distances by wind or sometimes water (DiTomaso and Healy, 2007).

Vector Transmission (Biotic)

Longer distance dispersal is usually mediated by human or other animal activities such as being carried on vehicles, transported in mud or soil, on hooves or equipment, clinging to fur or hair, or passing through a digestive tract of an animal. In Chile, researchers found 32% germination of C. melitensis seeds distributed in rabbit faeces (Fernandez and Saiz, 2007), indicating that European rabbits were vectors. The presence of C. melitensis seeds in fleeces cleaned at woollen mills indicates that sheep transport the seeds (Nesom, 2004).

Accidental Introduction

All of the introductions appear to have been accidental, or at least caused by carelessness. Soil carried as ballast on ships appears to have been the most significant long distance dispersal mechanism between continents (Roché and Talbott, 1986). Movement with cereal grains probably also contributed (Dunn, 1905).

Impact on Habitats

The Forest Service included C. melitensis in the list of the invasive, non-native species posing the greatest threat to successful restoration of native vegetation in chaparral types following the 2003 Grand Prix/Old Fire in the San Bernardino Mountains of southern California (Hubbert, 2007).

After the fires, surveys for infestations of the target weed species found that C. melitensis covered large acreages. Fire disturbance aided the spread of weed infestations that were already present before the fire, either in the seed bank or in close proximity to the burn, including infestations of C. melitensis which expanded beyond the pre-fire levels, especially on fire roads. It was probably already established along roadsides before the fire, but was able to spread into new areas because of a lack of competition after the fire. Dozer lines, safety zones and hand lines were the second most infested areas and, in most cases, C. melitensis grew faster than the native species (Hubbert, 2007).

Impact on Biodiversity

The Forest Service is monitoring the expansion of a population of C. melitensis following the Cedar Fire in southern California chaparral and its potential impact on the habitat of the listed species Acanthomintia ilicifolia on Viejas Mountain (Hubbert, 2007).

• Proved invasive outside its native range
• Abundant in its native range
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Highly mobile locally
• Benefits from human association (i.e. it is a human commensal)
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually

• Ecosystem change/ habitat alteration
• Modification of successional patterns
• Negatively impacts agriculture
• Negatively impacts animal health
• Negatively impacts livelihoods
• Reduced native biodiversity
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition (unspecified)
• Rooting
• Produces spines, thorns or burrs

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field

Economic Value

C. melitensis is used in Spain for its stomachic, diuretic and hypoglycaemic properties (Negrete et al., 1989).