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Field thistle is a native weedy plant often found in disturbed areas, up to 8' tall, but usually much shorter. Flowerheads occur on the tips of branches, are light pink, and about 2" across. The base (involucre) of the flowerhead is vase-shaped and covered with multiple series of closely appressed, overlapping phyllaries/bracts (often said to look like fish scales). Each bract has a a medial white line and a single, sharp, 1/4" long golden spine at the tip. Below the involucre are a few slender bracts that look like miniature versions of the stem leaves; these bracts curve upwards around the flowerhead.

Cirsium

Cirsium discolor

field thistle [Blooms: Aug-Sep]

The base (involucre) of the 1.5-2" wide flowerhead of bull thistle is vase-shaped and covered with numerous series of imbricated, spreading phyllaries/bracts that taper into stiff, sharp points. The upper portion of the flowerhead consists of numerous pinkish-purple to purple tubular disk florets that split apically into five thread-like lobes and a single protruding style. This is the only North American thistle with spines (albeit, short) on the upper surface of the leaves and one of the few with spreading, spiny bracts at the base of the flowerhead; native thistles lack spines on the stems.

Cirsium

Cirsium vulgare

bull thistle [Blooms: Jun-Aug]

The flowers of both Claytonia caroliniana and Claytonia virginica occur in clusters (racemes) of 2-10 at the tip of the stem and are small (1/3-1/2") with long flower stalks. The flowers of both species contain (only) two green sepals; five petals with pinkish-purple stripes on a white background; five stamens with deeply purplish-pink anthers; and a single style that splits into three above its midpoint. The flowers of both species close at night or on cloudy days and nod down; they perk up and reopen when the light increases. The fruit of both species is a three-part, egg-shaped capsule nestled between the two sepals. Each capsule contains 1-6 shiny, black seeds 2-4 mm long which have a coating that attracts ants; the ants carry the seed off to their nests, thus dispersing them.

Claytonia

Claytonia caroliniana

Carolina spring beauty [Blooms: Apr]

Spring beauty flowers occur in a cluster of 2-10 at the tip of the stem. The flowers are small (1/3-1/2") with long flower stalks; they contain (only) two green sepals, five petals with pinkish-purple stripes on a white background, five stamens with deeply purplish-pink anthers, and a single style that splits into three above its midpoint. The flowers close at night and on cloudy days and nod down; they perk up on reopening. The fruit is an three-part, egg-shaped capsule nestled between the two sepals.

Claytonia

Claytonia virginica

spring beauty [Blooms: Apr-May]

Asiatic dayflower flowers are 0.5-1" across; they have two thin, blue upper petals and a single, lower, translucent white petal with three lobes. There are 5-6 long stamens with yellow anthers highlighted by a central dot of maroon; the upper three stamens are sterile and probably only serve as an advertisement, while the lower two bear larger anthers with viable pollen. A single long style lies below the stamens. Below and behind the flower is a leaf-like bract (spathe) 1-2" long that is open to its base and embraces the flower like a hammock.

Commelina

Commelina communis

asiatic dayflower [Blooms: Jun-Oct]

Upper stems of poison hemlock bear compound umbels 2-5" wide of tiny (1/8") white flowers with five spoon-shaped petals (one often larger than the others), usually with a longitudinal fold and notched; below the umbels are oval bracts with elongate tips, not divided like the leaves.

Conium

Conium maculatum

poison hemlock [Blooms: May-Jun]

Lily-of-the-valley's raceme bears 6-14 bell-shaped, 8 mm long (and wide), white flowers on one side of the stalk; it often nods at its tip. Individual flowers are bell-shaped with six recurved, pointed lobes around the mouth, white to light green, with six stamens and a single style with a three-lobed stigma hidden inside. The corolla is pendant, dangling from the raceme by 1/2" long, flexible pedicels that have light green, narrow bracts about as long as the flowers at their base.

Convallaria

Convallaria majalis

lily-of-the-valley [Blooms: Apr-May]

Field bindweed stems produce 1-4 funnel-shaped flowers, each arising from a leaf axil, about 1" across and cupped by five small sepals and attached to a flower stalk; the flower stalk bears two small bracts about 1" below the base of the flower. Flowers range from white to pink, with a clear yellow center containing five stamens and a single style with a split stigma. Each bloom lasts only one day.

Convolvulus

Convolvulus arvensis

field bindweed [Blooms: May-Aug]

Horseweed flowering stems form a pyramidal inflorescence covered with numerous flowers and what look like dandelion seedheads. Panicles of flowers up to 1.5' long 6" across arise from the tip of the main stem and from axillary stems that arise from the upper leaves. Individual flowers are small (~1/8" in diameter and 1/4" long), cylindrical or urn-shaped, and covered with multiple layers of phyllaries; they look more like buds than flowers with only the tips of the 25-45 white or pink, pistillate ray florets peeking out the end. The 12-25 disk florets are yellow; they bear both pistils and stamens.

Conyza

Conyza canadensis

horseweed [Blooms: Jul-Aug]

Lance-leafed coreopsis flowerheads are 2-3" across; they have about eight broad, yellow ray florets with 3-5 (usually four) bold, sawtooth lobes at their tips (that may also be subdivided); the numerous disk florets are also yellow, tubular, about 1/4" long with 4-5 tiny lobes. The seeds are black, egg-shaped, and 2.5-5 mm long with thin papery wings along the edges.

Coreopsis

Coreopsis lanceolata

lance-leafed coreopsis [Blooms: May-Jun]

Prairie coreopsis flowerheads occur alone or in pairs on 1/2-2" long peduncles attached to the ends of stems. Each flowerhead is about 2" across with 8-12 ray florets; two prominent longitudinal veins divide each ray floret petal into thirds. The disc florets are tubular with 4-5 lobes; they are initially yellow, but turn brownish with age.

Coreopsis

Coreopsis palmata

prairie coreopsis [Blooms: Jun-Jul]

Plains coreopsis flowers are 1-2" across, with 6-12 (usually 8) ray florets, each with three lobes at their tips (center largest). The ray florets are sterile, typically yellow at their tips, transitioning abruptly to a maroon color more basally. The disk florets are perfect (have both anthers and pistils), reddish-brown to maroon with the florets at the edge of the disc with bright yellow highlights (either the anthers on the fused stamens or the split stigma of the pistils); individual florets have four teeth/lobes. The involucre of the flowerhead is often reddish-tinged, particularly obvious when cupping the developing seedhead.

Coreopsis

Coreopsis tinctoria

plains coreopsis [Blooms: Jun-Oct]

Tall coreopsis flowerheads arise from peduncles up to 10" long; the flowerheads are 1.5-2" across with eight sterile, yellow ray florets (each with two deep folds that divide the ray florets longitudinally into thirds) and numerous reddish-purple, fertile disk florets. The corollas of the disc florets are tubular, with 4-5 triangular lobes at their tips, and about 5 mm (~1/4") long; each has five stamens (fused together at their tips) with yellow anthers, and a single bifurcated style with pointed tips.

Coreopsis

Coreopsis tripteris

tall coreopsis [Blooms: Aug-Sep]

Whorled coreopsis' flowerheads are a bright golden yellow, 1-2" across, with eight yellow, elongate egg-shaped ray flowers and numerous (30-40) yellow disk flowers.

Coreopsis

Coreopsis verticillata

whorled coreopsis [Blooms: Jun-Sep]

Silky dogwood flowers occur in flat to convex clusters (cymes) 1-2.5" across. Individual flowers are about 3/8" across with four sharp sepals, four creamy-white, lance-like petals, four stamens about as long as the petals, and a single, stout, green-tipped style arising from an amber ovary. The flower stalks are silky-hairy.

Cornus

Cornus amomum

silky dogwood [Blooms: May-Jun]

Rough-leaved dogwood is a shrub/tree that can be as much as 20' tall. Cymes of white flowers 2-4" across arise from the leaf axils; the upper bounding surface of the cyme is flat or gently rounded. The fruit (a drupe) is white, about 1/4" across, and spherical; as it ripens, the branches of the cyme turn deep red. The fruit is very attractive to wildlife.

Cornus

Cornus drummondii

rough-leaved dogwood [Blooms: ?]

Cornelian cherry dogwood is a European exotic that has been planted in Jackson Park. Flowers appear in umbels before the leaves emerge. The flowers are small (1/8"), with four bright yellow, lance-shaped petals, four stamens, and a cone-shaped, hairy receptacle; the single pistil emerges from the center of the ovaries. The fruit is an oblong, dark red drupe about an inch long.

Cornus

Cornus mas

Cornelian cherry dogwood [Blooms: Apr-?]

Swamp dogwood's flat-topped panicles of flowers are 2-3.5" across. Single flowers are about 1/4" across with a light green, tubular calyx, four lance-shaped white petals, four stamens, and a single style.

Cornus

Cornus obliqua

swamp dogwood [Blooms: Apr-Jun]