Common Australian Garden Weeds

Cirsium vulgare

Scientific name: Cirsium vulgare (Savi) Tne.


Habit of spear thistle (Cirsium vulgare) immediately prior to flowering.


The spiny and purple flower-head of spear thistle.


The leaves of spear thistle are dissected and with numerous prickles and spines.


Close-up of leaf tip showing spine.


The seeds of spear thistle are released into the air.


Seedling of spear thistle.

Synonyms: Carduus vulgaris Savi.; Cnicus lanceolatus (L.) Scop.

Common names: Spear thistle, Scotch thistle

Family: Asteraceae

Origin:

Native of Europe, western Asia and northern Africa.

Habit:

Annual or biennial herb, reaching 1.5m in height and developing a large taproot. Stems, leaves and flower heads are very spiny. Flower-heads are showy purple thistles.

Habitat:

Weed of untended areas such as road sides and pastures.

General description:

Stems and leaves

Stems are ridged longitudinally with spiny wings where the edges of the leaves continue down the stem. Some plants have hairless stems while others have dense covering of woolly white hairs. Young plants have leaves arranged in a rosette. Basal leaves are 45 x 10 cm, ovate to narrowly ovate i.e. with a highly divided (pinnatifid) margin with spines at the tips of the lobes. Upper leaves are smaller, up to 1.5-4 cm, also having (pinnatifid) margins but with spiny lobes projecting upwards and downwards with 1.5 cm long spines at the apices of each lobe. Leaf blades have a dense, white, woolly under-surface and an upper surface with short, stiff, close-lying hairs.

Flowers and fruit

Flower-heads are borne singly at the ends of leafy branches. There are no ray florets. Disc florets are purple and extend outwards from a spiny, ovoid base (involucre) 3-5 cm long. Seeds are achenes 2.5-4 mm long with a pappus of 0.8-1.1 cm long feathery bristles, which falls off the fruit rather quickly. The seed is greyish, with brown and ochre streaks, 1 x 3 mm with a deeply sunken apex.

Distinguishing characteristics:

Large purple thistle with deeply lobed leaves. Each leaf lobe ends in a rigid spine. Further scattered prickles on the upper surface of the leaves. White woolly under-surface of the leaf. Juvenile leaves form a rosette.

Noxious status:

It is declared noxious in Victoria, South Australia and Tasmania.

Sources:

Kleinschmidt, H.E., Holland, A. and Simpson, P. (1996). Suburban Weeds. 3rd Edition. Department of Primary Industries, Brisbane.

Stanley, T.E. and Ross, E.M. (1983-1989). Flora of South-eastern Queensland. Volume 2. Department of Primary Industries, Brisbane.

Anonymous. (2000). Noxious Weed List for Australian States and Territories. Prepared by the National Weeds Strategy Executive Committee.

Anonymous. (1994). Queensland Vacsular Plants: Names and Distribution. Queensland Herbarium, Brisbane.