Prickly sow thistle resembles a spiny thistle plant bearing yellow dandelion flowers. Often growing to 5 feet in height, this native of Europe commonly grows in moist, open, disturbed habitats.
Prickly sow thistle is a taprooted annual easily growing to 5 feet tall. It is usually a glabrous (smooth) plant, but sometimes there are rusty-colored gland-tipped hairs toward the top.
- Like dandelion, chicory, and other members of its tribe, this plant bleeds a milky sap when cut.
The flowerheads look a lot like those of dandelions, about ¾ inch across; the florets are lemon yellow to bright yellow. The base of the flowerhead may be smooth or have hairs. The flowerheads mature into fluffy seed heads similar to those of dandelions.
Blooms May–October.
The leaves are basal as well as alternate on the stem; they become smaller higher on the plant. They are irregularly, deeply lobed; higher on the stem, the leaves are increasingly less deeply lobed. The leaf margins are toothed, with rather stiff, short, slender prickles at the tips. The upper surface is dark green and shiny; the lower surface is pale and sometimes has a white-waxy coating.
- The leaves have their clasping basal lobes (not counting the prickles) rounded (not sharply pointed).
Similar species: Two other species of sow thistles (genus Sonchus) have been recorded in Missouri:
- Common sow thistle (Sonchus oleraceus) is very similar to prickly sow thistle, is about as common, and lives in similar habitats. Both are introduced (native to Europe). The key difference is that at the base of the leaves, where they attach to the plant stem, the clasping basal lobes are sharply pointed (not rounded).
- Field sow thistle, or perennial sow thistle (Sonchus arvensis), is another nonnative species but has only rarely been collected in Missouri. Its flowering heads are bigger (¾ to 1¾ inches across), and it’s a perennial, with deep-set, branching rhizomes.
Blooming height: from 4 inches to 5 feet, sometimes taller.
Scattered nearly statewide.
Habitat and Conservation
Nonnative; occurs on banks of streams and rivers and in disturbed bottomland prairies; also in pastures, along margins of crop fields, and in fallow fields, cemeteries, gardens, barnyards, railroads, roadsides, and other moist, disturbed areas.
Status
Nonnative wildflower, often considered a weed. Declared noxious and invasive in some regions. All members of genus Sonchus are native to the Old World and not to North or South America.
Human Connections
Sow thistles are named because they were once fed to lactating sows, in the belief that they would increase milk production for the piglets. This antique reasoning held that the plant’s milky sap meant that it would somehow enhance the sow’s ability to give milk.
Wild edibles enthusiasts seek out the leaves of young sow thistle plants.
- Like wild lettuces and dandelions, the key to enjoying them is to pick them young and tender (before they send up a flowering stalk): before they become bitter, and before the leaves develop a lot of prickles.
- Of course, you may not be able to identify the plant for certain when it is so young. Please use caution.
- Cooking methods are like those you’d use with lettuces, kale, or chard.
Ecosystem Connections
Pigs and people are not the only animals that eat sow thistle leaves. Although the bitter sap of older plants probably reduces their palatability, deer, ground squirrels, and other herbivores eat this species.
Numerous bees, butterflies, and flower flies insects visit the flowers for pollen and nectar. Aphids suck the juices. Several other insects eat the foliage or burrow into the stems or leaves, eating it from within. These insects, in turn, become food for birds and other insectivores.
Despite its name, this plant is not a thistle.
- Although both thistles and sow thistles are in the sunflower-daisy family, thistles are their own tribe (which also contains cornflower and knapweeds).
- But sow thistles are in the chicory tribe, along with dandelion, salsify, hawkweeds, and lettuces.
- The chicory tribe has special flowerheads, with all ligulate florets (strap-shaped, with 5 teeth and the tip), and all bleed a milky sap.
