Herb up to 60 cm, greyish-green, with flowers arranged in small off-white spherical flower heads.
Scientific name: Conyza bonariensis (L.) Cronq.
Common names: hairy fleabane, Argentine fleabane, fleabane
Family: Asteraceae (Compositae)
Status in Portugal: invasive species (listed in the Decreto-Lei nº 92/2019, 10 july)
Risk Assessment score: 26| Value obtained according to a protocol adapted from the Australian Weed Risk Assessment (Pheloung et al. 1999), by Morais et al. (2017), according to which values above 13 mean that the species has risk of having invasive behavior in the Portuguese territory | Updated on 30/09/2017.
Synonymy: Erigeron bonariensis L., Erigeron linifolius Willd., Leptilon bonariense (L.) Small, Leptilon linifolium (Willd.) Small
Last update: 09/07/2021
How to recognise it
Annual herb up to 60 cm, covered in short hairs that confer a greyish-green tone to the plant; simple primary stem with terminal panicles, posteriorly with long branches that overtop the main axis.
Leaves: greyish, pilose on both surfaces; basal leaves oblanceolate, entire or with 2-5 coarse lobes on each side; upper leaves smaller, linear–oblong, entire and sessile.
Flowers: arranged in capitula whose involucral bracts are densely hairy; ligules that are hard to observe (< 0,5 mm).
Fruits: dirty-white cypselas, each one with a pappus of 4-5 mm; (open) capitula with 8-15 mm diameter.
Flowering: June to August.
Similar species
The several Conyza species in Portugal are very similar and hard to distinguish. Additionally, the Conyza species hybridize very rapidly among themselves, originating hybrids with intermediate characteristics, causing further difficulty in the identification.
Conyza bonariensis is distinguished from the other species of Conyza (Conyza canadensis, Canadian fleabane, and Conyza sumatrensis, tall fleabane) for having a smaller plant syze and for having bigger and denser capitula (on the fruit) with dirty-white cypselas. It is also the only species that presents the shorter main axis overtopped by the lateral branches.
Inflorescences: comparison of the three most common Conyza species in Portugal.
Characteristics that aid invasion
It propagates by seed, producing high amounts of seeds (2000 to 230000 seeds per plant) of reduced persistence (2 to 3 years) and a graduated germination. The seeds are efficiently dispersed by the wind, rapidly enhancing their distribution area.
Native distribution area
South America.
Distribution in Portugal
Mainland Portugal (all provinces), Azores archipelago (all islands), Madeira archipelago (islands of Madeira and Porto Santo).
Geographic areas where there are records of Conyza bonariensis
Other places where the species is invasive
Europe (Spain, France, Italy, Croatia, Greece, Malta, Albania, Czech Republic), South Africa, Australia, New Zealand, Oriental Africa, North America (Mexico and USA), Central America.
Introduction reasons
Probably accidental, very ancient.
Preferential invasion environments
A ruderal weed species,very frequent in disturbed areas: urban areas, roadsides and crop fields or common lands. It also appears in natural and semi-natural areas (e.g., dunes) normally associated to disturbance events.
