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Clusters of 4-8 flowers begin to bloom before the leaves emerge on Eastern redbud; the buds (lower left) are rosy-pink, turning a lighter pink when the flowers open. Individual flowers are about 1/2" long, on pedicels 1/4-1/2" long, pea-like with an upper central petal (the banner), two upper lateral petals (the wings) and two lower petals (usually a darker pink) that form the projecting keel; a short purplish tubular calyx with five blunt teeth lies behind the corolla. The keel encloses ten stamens and a single curved style.

Cercis

Cercis canadensis

Eastern redbud [Blooms: Apr-May]

Wild chervil upper stems terminate in up to three clusters of 3-7 small, white flowers (right image). Individual flowers (upper left) are tiny (1/8" across), each with five white petals, five stamens, and a cylindrical green ovary bearing a split style; the sepals are highly reduced. After fertilization, both the cylindrical ovary and the flower stalk elongate; mature fruits (lower left) are usually hairless, about 1/4" long, and contain a single seed.

Chaerophyllum

Chaerophyllum procumbens

wild chervil [Blooms: May-?]

Partridge pea flowers are ~1" across, noticeably asymmetric, with five yellow petals with red blotches at their base; the lowermost petal is about twice the size of the other petals. One of the lateral petals curls around the stamens. There are ten reddish-purple stamens and a single greenish-yellow style (longer than the stamens) that curves upward towards the tip; nine smaller stamens lie on one side of the style and one larger stamen on the other.

Chamaecrista

Chamaecrista fasciculata

partridge pea [Blooms: Jul-Oct]

Lamb's quarters produces inconspicuous star-shaped, yellow-green flowers, <1/8" across, sessile on flower stalks in round, tight clusters; the flowers have no petals, five stamens with yellow anthers, and a single divided style at the tip of a round, green ovary, all cupped in a five-lobed, mealy-white, calyx. The flowers are wind-pollinated and can aggravate hay fever symptoms.

Chenopodium

Chenopodium album

lamb's quarters [Blooms: Jul-Sep]

"Canada thistle" is a calumny on poor Canada; this homely plant is native to Eurasia, not our northern neighbor. Flowerheads of Canada thistle are much smaller (1/2-3/4" across) than those of bull or field thistle and often occur in clusters on the plant. The involucre is goblet- rather than vase-shaped, covered by closely appressed green to purplish phyllaries, that have short, sharp, brown tips but no spines; there are only tubular disk florets with five thread-like, 1/4" long apical lobes, pink or pale lavender (rarely white) in color.

Cirsium

Cirsium arvense

Canada thistle [Blooms: May-Sep]

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]

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]

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]

Cockspur hawthorn produces flat-topped panicles of flowers 2-3" across that arise from leaf axils; the panicle branches are light green and hairless. Individual flowers are 1/2" across; they have a green calyx with five teeth, five spreading white petals, 10-20 stamens with pink or pale-yellow anthers, and a pistil with 2-3 styles. At least in Jackson Park, the upper surface of the receptacle at the base of the pistil is a shiny greenish-yellow to reddish-yellow. The flower's scent is not pleasant to humans but bees and syrphid flies are not deterred. The fruit is a small (1/2" across) crabapple-like pome, red at maturity.

Crataegus

Crataegus crus-galli

cockspur hawthorn [Blooms: May-Jun]

Downy hawthorn produces clusters of 5-17 flowers; the flower stalks are reddish-green and hairy. Individual flowers are 3/4-1" across with five green, triangular sepals with glandular hairs along the margins that are fused at their base; five round, white petals; 17-20 stamens with pale yellow or white anthers; and 4-5 styles. In Jackson Park, the top of the receptacle (at the center of the flower around the bases of the styles) is reddish-green to deep red and shiny.

Crataegus

Crataegus mollis

downy hawthorn [Blooms: Apr-May]

Common hawthorn produces broad, dense, flattened clusters (cymes) of five to fifteen flowers. Individual flowers are up to 1/2" wide with five reflexed sepals, five white petals, 15-20 stamens with red to purple anthers, and a single style. At least in Jackson Park, the upper surface of the receptacle at the base of the pistil is a shiny yellowish green.

Crataegus

Crataegus monogyna

common hawthorn [Blooms: May-?]

Spring crocus (Crocus vernus) is native to alpine regions of Europe, but widely escaped from domestic gardens in the U.S. Given its early blooming and short duration, it probably qualifies as a "spring ephemeral." The plant is short (4-6") but blooms before most other plants emerge. the leaves are 3-6" long and less than 1/4" wide, dark green with a distinctive silver-white medial stripe. Flowers are up to 6" tall, bell-shaped, 1-1.5" wide with six white to purple tepals in two overlapping whorls of three; the stamens are white with long yellow or orange anthers, the styles are yellow-orange, three-lobed, with a fringe of narrow processes. You'll know it when you see it.

Crocus

Crocus vernus

spring crocus [Blooms: Mar-Apr]

Honewort's inflorescence is a compound umbel 1.5-3" across of tiny (1/8") flowers. Each flower has five stamens with creamy-yellow anthers, and one or two light green, conical pistils; the five petals are usually curled in. In Jackson Park, flowers of honewort have two conical styles, whitish to greenish, that are shorter than the petals.

Cryptotaenia

Cryptotaenia canadensis

honewort [Blooms: May-Jun]

Winged pigweed flowers are whitish-green, sessile, and 1/16" across; the flowers have five inward-curving sepals that cover the ovaries, five stamens, and a flattened ovary with 2-3 styles. Flowers may contain only a pistil or both a pistil and stamens; if the latter, the creamy-yellow anthers are prominent.

Cycloloma

Cycloloma atriplicifolium

winged pigweed [Blooms: Jul-Aug]

White prairie-clover produces 1-3" long spikes of flowers and flower buds which open progressively from the base of the spike to the tip. Individual flowers are tiny (about 1/4" across), pea-like, white, with five petals (one much larger than the other four); five white stamens with pale yellow anthers protrude beyond the edge of the flowers.

Dalea

Dalea candida

white prairie-clover [Blooms: Jun-Jul]

At the apex of a purple prairie-clover stem is a 1-2.5" long spike of flowers and flower buds which open progressively from the base of the spike to the tip. Individual flowers are tiny (1/4" across), pea-like, deep magenta in color, with five purple petals (one much larger than the other four). Five stamens with golden anthers protrude beyond the edge of the flowers.

Dalea

Dalea purpurea

purple prairie-clover [Blooms: Jun-Aug]

Shrubby cinquefoil flowers are 3/4-1.5" across, bright yellow, with petals that are circular and overlap, 15-20 stamens with golden anthers, and numerous pistils clumped in the center. The five sepals are largely hidden behind the petals; only the sepal's tips protrude.

Dasiphora

Dasiphora fruticosa

shrubby cinquefoil [Blooms: May-Jul]