Centaurea melitensis
(Maltese starthistle)

Pictures

Picture	Title	Caption	Copyright
Title Flower Caption Centaurea melitensis; flowering head. Copyright ©Cindy Roché	Flower	Centaurea melitensis; flowering head.	©Cindy Roché

Identity

Preferred Scientific Name

• Centaurea melitensis Linnaeus, 1753

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

Summary of Invasiveness

C. melitensis is native to northern Africa and southern Europe in the western Mediterranean region, and has successfully invaded similar climates in the USA, New Zealand, Australia and South America. In favourable habitats it can form dense stands that replace native and desirable vegetation. It is commonly less aggressive than Centaurea solstitialis and in some areas grows as a minor forb in annual grasslands. C. melitensis usually invades open, disturbed sites and is often spread by humans and livestock and by transportation of contaminated soil, crop seed or hay (DiTomaso and Healy, 2007).

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

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.

Description

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).

Plant Type

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

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).

Habitat

Habitat List

Biology and Ecology

Climate

Soil Tolerances

Soil drainage

• free

Soil texture

• light
• medium

Special soil tolerances

• infertile
• shallow

Means of Movement and Dispersal

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).

Pathway Causes

Pathway Vectors

Impact Summary

Environmental Impact

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).

Threatened Species

Risk and Impact Factors

• 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

Uses

Economic Value

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

Uses List

Human food and beverage

• Honey/honey flora

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical

Similarities to Other Species/Conditions

C. melitensis and C. solstitialis might be confused by someone unfamiliar with both species. Both are winter annuals that invade similar habitats and have spiny phyllaries and yellow flowers. The central spines of C. melitensis are shorter (5-12 mm) than those of C. solstitialis (10-25 mm) and are branched closer to the tip. They are purplish to brown-tinged compared with the yellowish to straw-coloured spines of C. solstitialis. The senescent flower heads of C. melitensis retain the spined phyllaries and shed the fuzzy centre (leaving an empty ‘bowl’), whereas those of C. solstitialis shed the spined bracts and retain the fuzzy centre (leaving a cottony tip) (DiTomaso and Healy, 2007).

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

Biological control

A small beetle (Lasioderma haemorrhoidale) that feeds in the capitula of C. melitensis was unintentionally introduced in California from the Mediterranean region, but has had little impact on controlling C. melitensis populations (DiTomaso and Healy, 2007). It is a generalist seed feeder that also attacks C. solstitialis, C. sulphurea and Carduus pycnocephalus. Two other agents introduced for C. solstitialis, Chaetorellia succinea and Eustenopus villosus, also utilize C. melitensis, but to a lesser extent (DiTomaso and Healey, 2007). In host specificity tests, there was significant larval development by the Eurasian weevil Ceratapion basicorne on C. melitensis (Smith, 2007).

Chemical control

C. melitensis is susceptible to the same chemicals as other Centaurea species, including phenoxy acetic acid (2,4-D), benzoic acid (dicamba), pyridines (triclopyr, aminopyralid, clopyralid, picloram), imidazolinones (imazapic), semicarbazone (diflufenzopyr) and glyphosate. Recommended rates and application times for the Pacific Northwest states are given in Peachey (2009).

Control by utilization

Cattle may graze C. melitensis if adequate palatable forage is lacking, but the amount of use under normal conditions is probably minimal. Sheep and goats would probably be more effective, but have not been studied. They could also contribute to spread of the weed.

Ecosystem Restoration

In an experiment in the Sequoia National Park, California, USA, annual grasslands dominated by exotic annuals were burned once in the spring or autumn or in two or three successive years in the spring or autumn to convert them to native perennial bunchgrasses. Both burning regimes increased the number of alien and native forb species without establishing any native grass. C. melitensis, which was not encountered in any plots before burning, accounted for most of the alien forb response (Parsons and Stohlgren, 1989). DiTomaso et al. (2001) burned for 2 consecutive years in the late spring or early summer for control of barb goatgrass (Aegilops triancialis) and noted a decrease in the frequency of C. melitensis on annual grassland in California.

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Links to Websites

Contributors

13/11/09 Original text by:

Dominique Roche, McGill University - STRI, Department of Biology, Canada

Distribution Maps