Common/Bull Thistle

Cirsium vulgare Asteraceae/Compositae

I collected (with difficulty) a dead thistle near some trashcans behind a greenhouse. This non-native is differentiated from native thistles by decurrent spines that grow down the stem and reflexed (turned down) spiny bracts at the base of the flower heads. I love the visual aspects of this plant, the complexities of its morphology or structure but don’t like to touch it, an obvious survival adaptation.

Ecology: provides seeds for granivores (consumers of grains and seeds) if fruits are left. Pollinators get nectar and pollen, but it is aggressively invasive. It can be a ruderal or first to colonize bare land disturbed naturally, or by agriculture and development.

Left above: Eastern Bumble Bee (Bombus impatiens) has a black head, a black bald spot on its yellow thorax, and a yellow stripe on its abdomen (8-19-18). Right: Sweat Bees (Halictid sp). Skinny pale stigmas poke up between darker fused anthers that hold pollen.

Roots and Shoots (stems, leaves and hairs). A biennial that establishes a deep tap root with a rosette of leaves in the 1^st year (below left). The stem is very short between the radiating leaves. In the 2^nd year when the stem lenghthens to produce flowers and fruits, the leaves are deeply divided into lobes that end in spines. (right)

Hairs: Pubescent is the overall term for any kind of hairs. This is what happens when you “look closely” the way Gleason and Cronquist do (see Resources page): “decurrent leaf bases, copiously spreading-hirsute to sometimes arachnoid; lvs strongly spiny, pinnatifid, the larger ones with the lobes again toothed or lobed, scabrous–hispid above, thinly white tomentulose to green and sometimes green and merely hirsute beneath.” Looking up most of these words (I know “or” “and” and “the”): Hirsute: coarse or stiff but not pungent, often bent or curved hairs, coarser than villous but less firm and sharp than hispid which is sometimes pungent. Pungent is firmly sharp-pointed, especially if thereby rendered uncomfortable to the touch or grasp. Arachnoid: cobwebby, with relatively long and tangled hairs. Scabrous: rough to touch, due to presence of short, stiff hairs. Tomentulose: diminutive of tomentose or tangled or matted wooly. These definitions are from the G&C Glossary.

So… very variable hairs (below).

Flower: I was consistently visiting a field on a restored farm waiting to see the thistle flower on a tall, 2nd year shoot (among other things). After I saw the buds, I knew the flower would open soon. On my next visit I was devasted to find a mowed field. Luckily a friend had this flower blooming along her road in Maine with several stages on the same shoot.

Inflorescence: The upper stems terminate in what looks like a single flower sitting on top of a flower stalk (peduncle). However, it is really a cluster of individual flowers (inforescence) called florets. They are all disk or tubular florets and not ray or strap florets, like a dandelion. I can’t see all the parts because they are packed so tightly and the top edge of each tube divides into 5 thin pink lobes to give it that distincitive look (below).

Flower parts: bracts, sepals, petals, stamens, pistil

Bracts: an involucre (whorl) of spiny bracts that surround the inflorescence. The lower ones are reflexed or turned down.

Sepals: some think these bracts are the sepals because they protect what seems to be an individual flower. Because the infloresensce isn’t one flower, some say the sepals are the hairy stuff (pappus) on individual florets that helps disperse seeds.

Petals: 5 thin pink lobes on top of 5 fused petals that form a tube.

Stamens: I could only see the fused anthers around the style (if I looked closely) and stigma of the pistil. The filaments (stalks) are hidden in with the pappus.

Pistil: the ovary, attached to the receptacle, will ripen into the fruit. The style or neck emerges from the pappus and lifts the pointed stigma to recieve pollen.

Left above: I dissected a thistle flower cluster on 9-1-18. At the top of the peduncle or flower stalk is the swollen receptacle where all the ovaries of the florets are attached beneath the hairy pappus.  The pink petals are at the top with thin stigmas poking out of fused anthers. Right: a drawing of a typical thistle floret.

Fruits/Seeds The ovary wall (pericarp) ripens around one seed and forms a fruit called an achene, a dry fruit that doesn’t dehisce or open to disperse its seed. An achene in the Asteraceae family is called a cypsela. It is a fruit that looks like a seed. The hairy pappus helps with wind dispersal (anemochory/ a-nem’-o-chor-e). Anemo (Greek for wind) Chore (Greek for spread).

Below: If you look closely you can see little white coccoon shapes attached to some of the hairy pappus clumps. They are the small cypselas ready to disperse when the wind comes along. Some clumps of pappus have already lost their fruits.

Below: closeup of 2 cypselas, one topped with pappus.

Taxonomy/Naming History

Cirsium, the genus name, is from the Greek word for ‘swollen vein’, because thistles were a medicinal remedy for this problem. Vulgare is from Latin meaning ‘common’. It is split into a sub-family and an even smaller group called a tribe. Sources don’t agree about this but I like to see the connection between an artichoke and a thistle.

Family: Asteraceae/ Compositae; Sub-family: Carduoideae- Artichokes Cynura; Tribe: Cynareae-Bull Thistle Cirsium vulgare. 

Globe Artichoke Cynura cardunculus.

What we eat is the bud. More specifically, a little bit of the peduncle (flower stalk), the soft pads inside the bracts surrounding the flower cluster, and the receptacle (the heart) where all the florets are attached. The choke is the pappus.

A Few Favorite Words:

Ruderal: first to colonize disturbed bare land

Arachnoid: cobwebby

Cypsela: an achene in the Asteraceae family.