Sonchus arvensis
perennial sowthistle [Blooms: Jun-Oct]
Perennial sowthistle (Sonchus arvensis) flowerheads and fruit. Bottom right: a perennial sowthistle flowerhead in three-quarters view. Top right: the backside of a perennial sowthistle flowerhead with its overlapping series of green phyllaries. Top left: lateral view of a perennial sowthistle flowerhead. Note the long, bifurcated styles. Bottom left: a perennial sowthistle seedhead. The brown seeds are only barely visible in the center of the ball of white hairs that will later loft each seed into the wind.
Perennial sowthistle’s upper stems produce long flower stalks at their tips. Individual flowerheads are 1-2″ in diameter, composed entirely of 80-250 yellow ray florets; disc florets are absent. The fruit, popular with goldfinches, is a flat, dark brown seed with tapered ends, several longitudinal ribs, and a tuft of fine white hairs (like a dandelion). Glandular hairs are typically present on the flower bracts and stalks; if these glandular hairs are absent, glands are present in the epidermis. Perennial sowthistle is indeed a perennial, one with a taproot that may penetrate as deep as nine feet into the soil. Of the local sowthistles, perennial sowthistle has by far the largest flowers; other species never exceed 3/4″.
Perennial sowthistle (Sonchus arvensis) stems and leaves. The leaf attachment to the stem is seen from behind (left) or the side. The stems are smooth and hairless; the margins of the leaves are decorated with soft “prickles.”
Perennial sowthistle (aka, field sowthistle) is an exotic from Europe, now naturalized to North America; it is considered a “noxious weed” in Illinois. This 2-4 feet tall, weedy plant has dandelion-like flowers and hairless stems that are dull green in color. The leaves are also dull green (although the upper surface of the leaf is often shiny), alternate, up to 12″ long and 3.5″ wide near the base of the plant, smaller in the upper parts. The leaves typically have 2-5 deep lobes with sharply pointed tips, giving the leaf a pinnate appearance, but occasional leaves, especially the smaller, upper leaves, may be unlobed. The margins of the leaves are densely decorated with sharp-tipped, soft “prickles” but the lower midvein lacks them; at the base of the leaves are small, rounded lobes that clasp the stem.
A perennial sowthistle (Sonchus arvensis) plant growing from a crack between cement blocks on the south shore of 59th St. Harbor. Note the seedheads near the top of the plant and some seeds caught by their tufts on the stems. The inset in the lower left corner shows several unopened flower buds and two open flowerheads.
Perennial sowthistle (aka, field sowthistle) is an exotic from Europe, now naturalized to North America; it is considered a “noxious weed” in Illinois. This 2-4 feet tall, weedy plant has dandelion-like flowers and hairless stems that are dull green in color. The leaves are also dull green (although the upper surface of the leaf is often shiny), alternate, up to 12″ long and 3.5″ wide near the base of the plant, smaller in the upper parts. The leaves typically have 2-5 deep lobes with sharply pointed tips, giving the leaf a pinnate appearance, but occasional leaves, especially the smaller, upper leaves, may be unlobed. The margins of the leaves are densely decorated with sharp-tipped, soft “prickles” but the lower midvein lacks them; at the base of the leaves are small, rounded lobes that clasp the stem. The upper stems produce long flower stalks at their tips. Individual flowerheads are 1-2″ in diameter, composed entirely of 80-250 yellow ray florets; disc florets are absent. The fruit, popular with goldfinches, is a flat, dark brown seed with tapered ends, several longitudinal ribs, and a tuft of fine white hairs (like a dandelion). Glandular hairs are typically present on the flower bracts and stalks; if these glandular hairs are absent, glands are present in the epidermis. Perennial sowthistle is indeed a perennial, one with a taproot that may penetrate as deep as 9′ into the soil. Of the local sowthistles, perennial sowthistle has by far the largest flowers; other species never exceed 3/4″. Perennial sowthistle has larger (1-2″ as opposed to less than 3/4″) flowers than the other two species and small, rounded lobes at the base of the leaves. The triangular lobes on the base of the leaves of common sowthistle (Sonchus oleraceus ) are not found in the other two species.
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![Evening primrose — clusters of yellow flowers occur at the apex of the plant. The flowers are 1-2" across, with four 1/2-1" long green sepals strongly reflected over a long (3/4-2"), green, cylindrical floral tube (the ovary is located just above the leaf axil), four heart-shaped yellow petals, eight stamens, and a single style with an X-shaped stigma. The sepals typically remain connected (in pairs) along one edge until the flower opens. The seedpods develop within the ovary (the base of the elongate floral tube); they are hairy, urn-shaped with rounded edges, and have four or eight small lobes on the apex. The seeds are claimed to remain viable in the soil for up to 70 years. The flowers open at dusk and close early in the day. — — — There are (at least) three evening primroses in Jackson Park — common evening primrose (Oenothera biennis), northern evening primrose (Oenothera parviflora), and hairy evening primrose (Oenothera villosa). They are easily confused with each other. (Judging by the conflicts between the accounts on Illinois Wildflowers [https://www.illinoiswildflowers.info/], Minnesota Wildflowers [https://www.minnesotawildflowers.info/], and Missouri Plants [http://www.missouriplants.com/], even the experts are confused.) All three species have yellow flowers with an X-shaped stigma, reflected sepals, petals with a small notch in their apex, stems that may be red or green, and lance-shaped leaves with short, widely-spaced teeth. Northern evening primrose is distinguished by (1) the presence of a knob or ridge at the tip of each sepal which the other two species lack (2) a seed capsule with four robust, flaring lobes with rounded tips at the apex of the seed capsule, and (3) a stigma that is very robust and almost fills the opening of the flower. Northern evening primrose has green to yellowish-green sepals. Hairy evening primrose (often but not always) has (1) striped or reddish-tinged sepals (check the buds where this character is often easier to see), (2) flowers that turn orange as they begin to senesce (although the reliability of this character is uncertain), and (3) always has glandular hairs covering the ovary that have "pimple-like" bright-red bases; these red pimples may also occur on the stems. All three species are somewhat similar to prairie sundrop (O. pilosella); the latter has very hairy stems and leaves, and translucent lines that radiate from the base of the petals in the flowers.](https://jacksonparkwildflowers.info/wp-content/uploads/2025/03/Oenothera_biennis-1t-300x300.jpg)
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