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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.

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]

Gray dogwood flowers occur in dome-shaped panicles with creamy-white branches 1.5-2.5" across and tall. Individual flowers are 1/4" across with a short calyx bearing four short teeth, four lance-shaped, creamy-white petals, four stamenns with pale yellow anthers, and a central, green-tipped style. The fruit is a small (1/4"), ball-shaped drupe, white when mature; when the fruit is mature, the branches of the panicle turn from white to bright red. Rough-leaved dogwood and red-osier dogwood also produce white fruit, but their panicles are flat-topped, not domed; the panicle branches are also not red in red-osier dogwood, but they are in rough-leaved dogwood so carefully inspect the stems (hairy) to see if the specimen in hand might be the latter.

Cornus

Cornus racemosa

gray dogwood [Blooms: May-Jun]

Red-osier dogwood flowers occur in flat-topped or slightly concave panicles 2-3" across; each flower is about 1/4" across with a small green calyx with four teeth; four white, lance-shaped petals; four stamens longer than the petals; and a single style rising from a reddish ovary. The fruit is a drupe about 1/4" across, white at maturity; the panicle branches remain green (unlike gray dogwood where the panicle branches turn red).

Cornus

Cornus sericea

red-osier dogwood [Blooms: Apr-Sep]

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-?]

Narrow-leaf hawksbeard is a weedy-looking plant that reaches a size of 8-40". Flowers occur in a panicle (usually arising from a leaf axil) with up to 20 dandelion-like flowerheads. Individual flowerheads are about 1" across with 30-70 yellow ray florets (the "petals"); beneath the ray florets are two layers of green bracts — an inner layer of 12-15 3/8" long, sharply-pointed, keeled bracts covered in wooly or short stiff hairs and an outer layer of bracts half the length of the inner layer, sometimes ridged, with hairs like the inner layer. Narrow-leaf hawksbeard can be distinguished from similar dandelion-like flowers (Crepis pulchera, Crepis capillaris, and various sowthistles and hawksweeds) by the presence of auricles on the stem leaves and a layer of appressed hairs on the inside surface of the inner bracts, best seen with a magnifier.

Crepis

Crepis tectorum

narrow-leaf hawksbeard [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]