Sonchus asper
prickly sowthistle [Blooms: Jun-Oct]
Prickly sowthistle (Sonchus asper) flowerheads. Top: buds and flowerheads of prickly sowthistle. Bottom right: face-on view of a prickly sowthistle flowerhead with its toothed “petals” and thicket of stamens and styles. Bottom left: lateral view of a prickly sowthistle flowerhead showing the phyllaries around the base of the flowerhead.
Prickly sowthistle’s flowerheads are dandelion-like, less than 3/4″ in diameter and composed entirely of 80-250 ray florets. Glandular hairs are present on both the flowerhead bracts and on the stalks just below the flowerheads. The fruits are flattened, brown, 2-3 mm long oval seeds with 3-4 ribs per side and a tuft of white hairs on one end. Prickly sowthistle has shiny green (as opposed to the dull green of the other two species) leaves with rounded lobes (as opposed to pointed lobes of common sowthistle) at the base of the leaves. Perennial sowthistle (Sonchus arvensis) has larger (1-2″ as opposed to less than 3/4″) flowers 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.
Prickly sowthistle (Sonchus asper) stems and leaves. Prickly sowthistle is instantly recognizable by the ear-like (or nautilus-shell-like) lobes where the leaf clasps the stem (1,2 — arrows). (3) The upper side of a stem leaf (3a) and the underside (3b) of the same leaf. (4) A prickly sowthistle stem with a series of alternate stem leaves, each with the characteristic ear-like basal lobes.
Prickly sowthistle, as the name implies, is a very prickly plant, 1-3 feet tall, branching occasionally in the upper half. The plant is an annual or biennial European exotic. The stems are green or reddish-green, round in section but hollow, with prominent longitudinal veins, usually hairless. Leaves are alternate, about three times longer than wide, up to 10″ long (usually less), shiny green, and often folded along the man vein. The lower leaves have margins divided into less distinct lobes than in common sowthistle; the upper leaves may be shallowly lobed or toothed. The leaves clasp the stem with two large, rounded, ear-like basal lobes that extend beyond the stem. (They remind me of the green, spiny cousin of a pearly nautilus shell.) Leaf margins are excessively prickly, but no prickles are present on the underside of the main leaf vein.
Two prickly sowthistle (Sonchus asper) plants, both growing on the north-east shore of East Lagoon. Note that the stems may be green, red, or a combination of the two.
Prickly sowthistle, as the name implies, is a very prickly plant, 1-3 feet tall, branching occasionally in the upper half. The plant is an annual or biennial European exotic. The stems are green or reddish-green, round in section but hollow, with prominent longitudinal veins, usually hairless. Leaves are alternate, about three times longer than wide, up to 10″ long (usually less), shiny green, and often folded along the main vein. The lower leaves have margins divided into less distinct lobes than in common sowthistle; the upper leaves may be shallowly lobed or toothed. The leaves clasp the stem with two large, rounded, ear-like basal lobes that extend beyond the stem. (They remind me of the green, spiny cousin of a pearly nautilus shell.) Leaf margins are excessively prickly, but no prickles are present on the underside of the main leaf vein. The flowers are dandelion-like, less than 3/4″ in diameter and composed entirely of 80-250 ray florets. Glandular hairs are present on both the flower bracts and on the stalks just below the flowers. The fruits are flattened, brown, 2-3 mm long oval seeds with 3-4 ribs per side and a tuft of white hairs on one end. Prickly sowthistle has shiny green (as opposed to the dull green of the other two species) leaves with rounded lobes (as opposed to pointed lobes of common sowthistle) at the base of the leaves. Perennial sowthistle (Sonchus arvensis) has larger (1-2″ as opposed to <3/4″) flowers 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)
![Northern evening primrose flowers are 3/4-1.5" across, have four yellow, heart-shaped petals, eight yellow stamens, and a cross-shaped stigma on a modest style; the stamens are as long or longer than the petals and the stigma is nearly fills the floral opening. At the base of the flower are four sepals 1/2-1" long, that bend back along the 3/4-1.5" long floral tube as the flower develops with pairs of sepals attached along one edge until the flower opens. Only northern evening primrose with a distinct ridge or knob near the tips of the sepals. The seed capsule develops from the ovary; it is 3/4-1.5" long, cylindrical but tapering slightly towards the tip, with four robust, flaring lobes at the tip. — — — 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 and is the only one of the three evening primroses to (sometimes) have reddish color on some or all of the midvein of the leaves. 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_parviflora-1t-300x300.jpg)
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