Onopordum illyricum

Name and classification

Onopordum illyricum L.
Family Asteraceae, Tribe Cynareae

Common names

Illyrian thistle

Disseminule

fruit

Description

Fruit an achene, obovoid, typically gibbous, somewhat compressed, 4–6 mm long, 2.5–4.0 mm wide, 1.5–2.5 mm thick; cross-section rhombic; surface light to dark brown, gray, or buff, with a variety of possible dark markings (from large splotches to tiny spots or mottling), widely-spaced wavy transverse ridges under numerous longitudinal ridges including 4 major ribs, glabrous. Scar basal, round, tan; often with a hardened elaiosome attached at the edge. Pappus cream-colored, 10–12 mm long, deciduous in a ring and often missing, leaving a brown apical collar measuring 0.8–1.7 mm at its widest. Style base a roundish to squarish stump. Embryo spatulate, cotyledons broad; endosperm absent.

Identification considerations

Fruits of various species of this genus look similar. Outside of its native distribution, Onopordum illyricum is most likely to be confused with three other invasive weed species: O. acaulon, which has a longer pappus (20–30 mm long); O. acanthium, which has a shorter pappus (7–9 mm long) that is pinkish instead of cream-colored; and O. tauricum, which also has a short pappus (8–10 mm long) that is pinkish.

Similar species

Onopordum acanthium L. (non-FNW)

Onopordum acaulon L.

Onopordum tauricum Willd. (non-FNW)

Distribution

native to Cyprus, Syria, Turkey, former Yugoslavia, Bulgaria, Greece, Italy, Spain, Portugal, and France, and most widespread in the western Mediterranean region

naturalized in Australia and California, United States

Habitat

sub-humid temperate regions, occurring in natural areas, on rocky hillsides, and on a variety of disturbed sites

General information

Onopordum illyricum is a biennial herb forming a rosette of deeply lobed leaves. Reproduction is sexual only; the plumed fruits are presumed to be wind dispersed. Dispersal may also occur via contaminated agricultural produce and vehicles, animal feet or fur, or along water channels. Fruits may be intentionally imported as the plants of the genus have been used for their antibacterial, hemostatic and hypotensive properties. They have also been grown as ornamentals. There are three subspecies: subsp. illyricum, subsp. cardunculus (Boiss.) Franco, and subsp. horridum (Viv.) Franco.

achenes without pappus, at the base of each achene is a light-colored, shiny appendage that is the elaiosome (on right side of the first and third fruits, on left side of the center fruit)

achenes without pappus, at the base of each achene is a light-colored, shiny appendage that is the elaiosome (on right side of the first and third fruits, on left side of the center fruit)

achene with broken pappus hairs

achene with broken pappus hairs

apex

apex

basal scar somewhat obscured by attached elaiosome

basal scar somewhat obscured by attached elaiosome

A, fruit; B, longitudinal section of fruit showing embryo; C, transection of fruit; drawing by Lynda E. Chandler

A, fruit; B, longitudinal section of fruit showing embryo; C, transection of fruit; drawing by Lynda E. Chandler