Herb up to 200cm, with flowers arranged in small off-white spherical flower heads.
Scientific name: Conyza sumatrensis (Retz.) E. Walker
Common names: tall fleabane, broad-leaved 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: Conyza albida Sprengel, Conyza albida Willd. Ex. Spreng.
Last update: 09/07/2021
How to recognise it
Annual herb up to 200 cm, with a robust look.
Leaves: greyish-green, densely hairy; the inferior leaves are lanceolate with indented margins; the upper leaves are linear-lanceolate, with entire margins.
Flowers: arranged in capitula whose involucral bracts are densely hairy; very small ligules, hardly noticeable to the naked eye.
Fruits: off-white cypselas, with a pappus of 3 mm diameter; capitula (open) with 4-8(10) 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 sumatrensis is distinguished from the Conyza bonariensis (hairy fleabane) by having a larger plant type (C. sumatrensis up to 200 cm; C. bonariensis up to 60 cm) and smaller open capitula (C. sumatrensis 4-8 mm; C. bonariensis 8-15 mm).
It may be distinguished from Conyza canadensis (Canadian fleabane) for having involucral bracts and densely hairy leaves (while C. canadensis has no hairs on the involucral bracts and the leaves have cilia only on the margin and on the midrib) and absence of well visible ligules.
Close-up of capitula: comparison of the three most common Conyza species in Portugal
Characteristics that aid invasion
It propagates by seed, producing a high amount of seeds that are efficiently dispersed by the wind, rapidly enhancing their distribution area.
Native distribution area
South America.
Distribution in Portugal
Mainland Portugal (all provinces), Madeira archipelago (Madeira island).
Geographic areas where there are records of Conyza sumatrensis
Other places where the species is invasive
Europe (Spain, France, Romania, Yugoslavia, United Kingdom).
Introduction reasons
Probably accidental, very ancient.
Preferential invasion environments
A ruderal weed species, very frequent in disturbed areas: urban areas, roadsides and croplands or common lands. It also appears in natural and semi-natural areas (e.g., dunes) normally associated to disturbance events.
