The genus Carduus Linnaeus
The words or terms in red
(actually dark orange) in the text are defined in a
The genus Carduus is not
native to North America; it was
introduced in the late 1800s, crowding out
the native species and forage for the
livestock; the genus is native to Eurasia and Africa.
The genus has about 90 species, 5 of which can be found in North America and
3 of them in Québec. The Carduus species are
biennials but rarely
They have a chromosome number (2n)
of 8, 9, 10, 11 or 13.
The species of the Carduus genus are at times quite similar to the
species of the Cirsium genus.
In fact, at one time botanists considered the
species of Cirsium to be Carduus
taxa. The only significant
difference between these two genera is the nature of
the pappus. The Cirsium species
can be distinguished from the Carduus species
by the plumose pappus of their seeds.
The members of the Carduus genus are known as plumeless thistles
because of their simple, not plumose, pappus. In the genus Carduus the
pappus is composed of capillary bristles
that are naked, single, and silky; whereas in the genus Cirsium the
pappus is composed of featherlike bristles.
The pappus must always be examined to determine the genus of an
The genus belongs to the
In Latin, cardus or carduus is the generic name
for the thistles as cited by the Roman poet Publius Vergilius Maro
(Vergil), 70 BC-19 BC, in De Georgica (The Georgics), a poem on
the subject of agriculture. Thistles include many
genera and many species of the subfamily
Cynareae of the Asteraceae family,
Cirsium, Silybum, Carduus etc.
It is also the name of the artichoke, (Cynara cardunculus var.
scolymus), cited by Plinius Secundus (Pliny the Elder), 23 AD-70 AD,
in Naturalis Historia (Natural History).
Although the artichoke does not belong to the Carduus genus there is
some similarity between the artichoke and thistles.
Carduus can reach 2 m in height and more, but some are not more than
30 cm high. They have erect stems that are simple too much branched.
They have basal and
cauline leaves. Their
blade margins are
The flower heads have disk florets only,
that are pink or purple.
Their phyllaries are in series, of half a
dozen to a dozen and tipped by a spine.
The seeds are ovoid cypselae with
a barbed pappus.
The Carduus of Québec
In Québec one can find three species of the Carduus genus:
It is not to difficult to differentiate these species;
Carduus nutans plants have larger
involucres, form 20 mm up to 70 mm,
than the other two species, up to or less than 20 mm.
Then, the abaxial leaf faces of
Carduus acanthoides are glabrate
except for long, curled, septate hairs
along the veins. The abaxial leaf faces of Carduus crispus are sparsely
to densely tomentose with fine non septate
hairs and often with curled, septate hairs along the veins as well.
- Carduus acanthoides subsp. acanthoides
- Carduus crispus
Carduus nutans (pictured above) with the two
- Carduus nutans subsp. leiophyllus
- Carduus nutans subsp. nutans