Vernonia missurica
Missouri ironweed [Blooms: Jul-Oct]
Missouri ironweed (Vernonia missurica) flowers and fruits. Bottom: a cluster of Missouri ironweed floral buds and flowerheads. Note the dark, scale-like phyllaries and the somewhat wider base of the receptacle. Top right: a cluster of Missouri ironweed flowerheads with a Peck’s skipper (Polites peckius) drinking the nectar from one floret. Note that the individual florets are easier to distinguish (and count) in the buds than in the mature flowerheads. Top left: a flowerhead post-fertilization. The tan-colored hairs are attached to developing seeds. The phyllaries are particularly clear in this image.
At the tip of a Missouri ironweed stem, a corymb of composite flowerheads (the inflorescence) is produced. The stems of the inflorescence are also covered in fine white hairs and usually reddish brown in color. Individual flowerheads are magenta and rayless; ray florets are completely absent. Flowerheads contain 32-60 disk florets, each 1/2-3/4″ across, which have rounded or broadly angled bracts (phyllaries) with sharp tips, dull green or reddish brown in color, that are layered like fish scales around the base. To sort out the Jackson Park ironweeds: (1) if both leaves and stem are densely covered with fine white hairs, the leaves are about 3-4 times longer than wide, and each flowerhead has more than 30 disk florets, it’s Missouri ironweed (V. missurica). (2) If both leaves and stems are hairless, there are less than 30 disk florets, and the leaves are narrow (typically a half inch or less; about 6-10+ times longer than wide), it’s smooth ironweed (V. fasiculata). (3) If the stems and leaves have only short hairs, there are less than 30 disk florets, and the leaves are about 2″ wide and 4-6 times longer than wide, it’s tall ironweed (V. gigantea).
Missouri ironweed (Vernonia missurica) stems and leaves. Left: a Missouri ironweed’s hairy stem with a series of alternately attached leaves. In the insert (upper left) is an enlarged view of a stem. Right: two views of the same Missouri ironweed leaf. The upper image shows the upper side of the leaf; the lower image shows the underside of the same leaf. The insert in the lower left of the lower image shows a further-enlarged view of the underside of a leaf; note the extensive hairs covering the veins and the leaf blade.
Missouri ironweed is a native perennial that ranges from 3-6 feet tall, unbranched except at the inflorescence; it is the commonest ironweed in Illinois. The stems are reddish-brown, stout, and covered with fine white hairs. The stem leaves are up to 7″ long and 2″ across (3.5 times longer than broad), lance shaped or narrowly ovate with very small, widely spaced serrations on the leaf margins. The undersides of the leaves are densely hairy, unlike other Veronia sp. in Jackson Park.
A stand of Missouri ironweed (Vernonia missurica) on the east side of the Old Rose Garden on Wooded Island. An enlarged image of a single flowerhead is shown on the lower right.
Missouri ironweed is a native perennial that ranges from 3-6 feet tall, unbranched except at the inflorescence; it is the commonest ironweed in Illinois. The stems are reddish-brown, stout, and covered with fine white hairs. The stem leaves are up to 7″ long and 2″ across (3.5 times longer than broad), lance shaped or narrowly ovate with very small, widely spaced serrations on the leaf margins. The undersides of the leaves are densely hairy, unlike other Veronia sp. in Jackson Park. At the tip of the stem, a corymb of composite flowerheads (the inflorescence) is produced. The stems of the inflorescence are also covered in fine white hairs and usually reddish brown in color. Individual flowerheads are magenta and rayless; ray florets are completely absent. Flowerheads contain 32-60 disk florets, each 1/2-3/4″ across, which have rounded or broadly angled bracts (phyllaries) with sharp tips, dull green or reddish brown in color, that are layered like fish scales around the base. To sort out the Jackson Park ironweeds: (1) if both leaves and stem are densely covered with fine white hairs, the leaves are about 3-4 times longer than wide, and each flowerhead has more than 30 disk florets, it’s Missouri ironweed (V. missurica). (2) If both leaves and stems are hairless, there are less than 30 disk florets, and the leaves are narrow (typically a half inch or less; about 6-10+ times longer than wide), it’s smooth ironweed (V. fasiculata). (3) If the stems and leaves have only short hairs, there are less than 30 disk florets, and the leaves are about 2″ wide and 4-6 times longer than wide, it’s tall ironweed (V. gigantea).
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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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