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Red chokeberry is a 6-12" tall shrub with multiple stems. Flowers are white with red tinge on the tips of the 5 petals; each flower is ~1" in diameter.

Aronia

Aronia arbutifolia

red chokeberry [Blooms: Apr-May]

Black chokeberry flowers occur in clusters of 7-12 near the margins of the shrub. Each flower is ~1/2" across with a reddish-green calyx with 5 short triangular lobes, 5 white, spoon-shaped, non-overlapping petals with rounded tips and a narrow base, 16-20 stamens with pink to rose-colored anthers, and 5 pale green styles, fused at their bases. The red glands on the upper leaf midvein and pink to rose-colored stamens are diagnostic of black chokeberry.

Aronia

Aronia melanocarpa

black chokeberry [Blooms: May-?]

Mugwort's Inflorescence consists of leafy spikes covered with inconspicuous flowerheads, initially whitish-green, later yellowish- or purplish-green; the flowerheads are egg-shaped, very small (1/8" across) and bear only disc florets (ray florets absent).

Artemisia

Artemisia vulgaris

mugwort [Blooms: Jul-Oct]

Prairie milkweed produces one and a half to two inch balls of 30-100 greenish-white flowers in the axils of a few of the mid-stem and upper leaves; the flowers are supported on 1/2"-3/4" pedicels. Each flower is about 1/8" across and 1/4" long; the flowers are a variation on the typical (complex) milkweed morphology with 5 sepals, a 5-lobed corolla with 5 petals (often with purple blotches at their tips) that are reflected backwards to cover the top of the pedicel, 5 hoods without horns, and a short central column that rises above the hoods; there is a distinct gap between the bases of the petals and the crown. Seedpods are 4-5" long with a fat base (attached to the pedicel) tapering rapidly to a narrow tip. Prairie milkweed can be confused with whorled milkweed (Asclepias verticillata) — both occur in Jackson Park — but whorled milkweed has even narrower (grass-like) leaves than prairie milkweed, is a shorter plant, and has pure white flower that do bear horns.

Asclepias

Asclepias hirtella

prairie milkweed [Blooms: Jun-Aug]

Butterfly weed has clusters of 8-25 flowers, in various shades of orange with touches of yellow or red, that arise from the stems and leaf axils. Individual flowers have a typical milkweed morphology, with the petals reflexed backwards over the flower stalk and the complex corona protruding. The central column of the corona in A. tuberosa is always yellow regardless of the shade of the remainder of the flower. This is the only Illinois milkweed with orange flowers and has narrower leaves than all other local milkweeds except whorled milkweed (A. verticillata, which has white flowers).

Asclepias

Asclepias tuberosa

butterfly milkweed [Blooms: Jun-Sep]

Canada milkvetch flower stalks are ~6" long, covered by numerous (up to 75) cream-colored, tubular flowers (right side of image). Individual flowers are 1/2-3/4" long, slightly drooping, with five petals making up the tube (like an elongated pea flower) and a short (~1/4") cylindrical calyx of the same color with five thin, green teeth; the tip of the upper petal is reflected upwards. The fruits (left side of image) are short, pea-like legumes packed tightly along the flower spike.

Astragalus

Astragalus canadensis

Canada milkvetch [Blooms: Jun-Aug]

White wild indigo is a striking plant that puts up 3-6' tall spikes of white flowers; the flower spikes alone are up to 2' long. Each flower is ~1" long and across with a elongate, triangular bract at the base of the flower pedicel. A short (1/2"), tubular, bluish-green calyx with four triangular teeth encloses the base of a white typical pea-like flower with a forward-leaning banner (one petal, folded up and back along the midline) and a pair of wings (two petals) that enclose a keel (two petals); the keel encloses ten green stamens with orange anthers and the single style.

Baptisia

Baptisia alba

white wild-indigo [Blooms: May-Aug]

Stems of cream wild indigo terminate in 3-9" long flower spikes that sprawl laterally or arch. Each flower is ~1" long and across with a short (1/2"), tubular, light green to light purple calyx with 4-5 triangular teeth, a creamy-yellow (or very yellow) typical pea-like flower with a vertical banner (one petal) and a pair of wings (two petals) that enclose a keel (two petals); the keel encloses ten stamens and the single style. Flowers are held on ~1" long pedicels; at the base of each pedicel, a lance-shaped, 1/2-1" long bract is sessile on the flower stalk. This is our earliest-blooming wild indigo. Flower color, the profuse hairs, and the bracts at the base of each flower pedicel are sufficient to positively identify cream wild indigo.

Baptisia

Baptisia bracteata

cream wild-indigo [Blooms: May-Jun]

Individual flowerheads of false boneset are about a half inch long and surrounded by green phyllaries. Each floret (inset) consists of 7-21 creamy-white, tubular florets with five lobes at the tip, and a prominent divided style protruding from the corolla.

Brickellia

Brickellia eupatorioides

false boneset [Blooms: Jul-Aug]

Purple poppy-mallow has hairy flower pedicels ~6" long that arise from leaf axils; the flowers are ~2" across, brilliant magenta, with an hibiscus-like (but shorter) white central structure containing the stamens and styles. The five calyx lobes are very hairy, shorter than the petals, and light green; beneath the calyx are three very similar bracts.

Callirhoe

Callirhoe involucrata

purple poppy-mallow [Blooms: ?-Jul]

The flowers of hedge bindweed are 2-3" long, formed from five white or pink fused petals; the throat of the trumpet is light yellow (less extensive than in field bindweed). The flowers are ephemeral, often lasting only a single day.

Calystegia

Calystegia sepium

hedge bindweed [Blooms: May-Sep]

American bellflower has deep blue flowers with a white center; they are about 1" across. The petals are ruffled, the style is long, arching, with a trifid stigma on its tip.

Campanula

Campanula americana

American bellflower [Blooms: Jul-Aug]

Creeping bellflower stems produce a terminal raceme of blue to purple flowers up to a foot long with all the flowers nodding towards the ground and all on the same side of the stem. Individual flowers are 1-1.5" long, borne on a short pedicel with a narrow, lance-shaped bract at its base. Each flower is bell-shaped with five pointed, recurved lobes with hairy margins and five green sepals at its base. There are 5 short curly, yellow stamens and a long style that emerges from the bell; the style has a three-part stigma at its end.

Campanula

Campanula rapunculoides

creeping bellflower [Blooms: Aug-Sep]

Nodding thistle is another heavily-defended exotic thistle, accidentally introduced to the U.S in the early 1900s. Solitary flowerheads are borne on long (up to 2'), whitish peduncles densely covered with short hairs. The flowerheads are 1-3" across, nodding (like the name says), made of 100-1000 tubular disk florets, each with its apical portion divided into 5 purplish-pink filaments and with a single, very long style. Beneath the large, showy flowerheads are stout, triangular, purplish phyllaries, each with a stout spine. When in bloom, the large size of the flowers and characteristic large phyllaries make it impossible to confuse with any of our other local thistles. Well loved by goldfinches, but considered a "noxious weed" by almost everyone else.

Carduus

Carduus nutans

nodding thistle [Blooms: Jun-Jul]

New Jersey tea flowers occur in panicles ("puffballs") up to 5" long and 3" across on peduncles up to 8" long arising from the tip of stems or axils of a leaf. Flowers are 1/4-3/8" across on 1/4-3/4" stalks; each flower has five triangular white sepals folded inwards towards the flower center; five widely spreading, white spoon-shaped petals with narrow bases and broad tips (tips curled in to heighten the "spoon" impression) emerging from between the incurled sepals; five stamens with whitish-purple anthers; and a three-part style.

Ceanothus

Ceanothus americanus

New Jersey tea [Blooms: Jun-Jul]

American bittersweet side branches occasionally produce panicles of flowers (up to 6" long) at their tips. Male flowers are about 1/4" wide with five light green petals with jagged or undulate margins, five green sepals, and five stamens with yellow anthers and a narrow style rudiment.

Celastrus

Celastrus scandens

American bittersweet [Blooms: Jun-Jul]

Common hackberry flowers may be staminate (male), pistillate (female), or perfect (both), all on the same tree. Flowers are about 1/4" across and bloom before the leaves open, often high in the tree (thus, I have no pictures yet). All flowers are wind-pollinated, yellowish-green with 4-6 spreading sepals joined at their bases; there are no petals. Male flowers have 4-5 stamens with green or yellow-brown anthers; female flowers have a green ovary with a large two-part, densely fuzzy style like an umbrella beneath the ovary. Perfect flowers have both.

Celtis

Celtis occidentalis

common hackberry [Blooms: Apr-May]

Spotted knapweed has pink to purplish flowers ~3/4" across composed of numerous tubular, branching, sterile ray florets with five lobes; the outermost ray florets are the longest. Disc florets ARE present, shorter and more erect than the ray florets but similar in appearance, with pink to white-tipped anthers and a divided style. The urn-shaped base of the flower is covered with tightly appressed oval bracts, each green with black tips; long, comb-like pale bristles radiate from the tip giving an appearance rather like a tick (inset).

Centaurea

Centaurea stoebe

spotted knapweed [Blooms: Jun-Sep]