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The tips of the upper stems of common groundsel produce dense clusters of flowerheads on short peduncles; inflorescences can also arise from leaf axils. Common groundsel flowerheads are cylindrical, 8 mm long and 4 mm across, with black-tipped, green bracts around the outside at both the base and the apex and 13-80 yellow disc florets peeking out the end; mature flowerheads are easily mistaken for flower buds. The disc florets have tubular yellow corollas, five stamens fused to the upper part of the corolla with yellow-brown anthers, and a bifurcated style with purplish stigmas. There are no ray florets. This is an easy plant to overlook. The flowerheads are twice as long as wide. The seedhead looks like a compact dandelion tuft with seeds on parachutes of light brown hairs.

Senecio

Senecio vulgaris

common groundsel [Blooms: May-Jul]

The five petals and five sepals of Maryland senna's 3/4" flowers are both yellow. The single pistil has many spreading white hairs and arches upward. The anthers of the 10 stamens are a striking dark brown (like partridge pea). The upper three stamens have short filaments and short anthers that produce only sterile pollen (as a pollinator reward). The middle four stamens have short filaments and long anthers while the lower three stamens have long filaments and long anthers; all seven of these stamens produce fertile pollen that is released by "buzz pollination." The flowers do not produce nectar. The fruit is a flattened seedpod 1/2" across and 3-4" long with 10-18 segments, each containing a single 1/4" flattened seed.

Senna

Senna marilandica

Maryland senna [Blooms: Jul]

Flower buds arise singly or in small groups on 1/2" long peduncles from the leaf axils. Because the flower peduncles are shorter (1/2") than the leaf petioles (1"), the flowers are often partly hidden among the leaves. Individual flowers are about 8 mm across. A flower contains five green, triangular sepals; five light yellow or light orange, rounded, floppy petals with pale lines that function as nectar guides and asymmetrical tips; and a central reproductive column (like mallows, to which prickly sida is related). That column consists of five styles fused along most of their lengths, each with a globose terminal stigma, and numerous stamens with yellow anthers. After fertilization, a circular seedpod forms from the five carpels; when mature, the seedpod turns brown and breaks into five segments, each containing a single reddish-brown, three-angled seed.

Sida

Sida spinosa

prickly sida [Blooms: Aug-Sep]

Evening campion is an exotic from Europe that grows to be 2-3' tall. It is nominally a night-blooming species, but I've observed it in bloom throughout the day in shady areas. Male and female plants are separate. The upper stems end in clusters of one or more 1-1.5" long flowers. The "bladder" (the calyx) is covered with a fuzz of fine hairs and has dark green or reddish-purple lines running from pole to pole (10 lines in male flowers, 20 in female). The five petals are heart shaped (with the point towards the center of the flower) and are deeply cleft into two lobes; the petals form a fringe that makes a distinct collar around the opening to the floral tube. Female flowers have five emergent styles (rarely four or six); male flowers have 10 yellow stamens that barely emerge from the collar at the center of the flower. (Other local Silene sp. have three styles.) The fruit is brown, urn-shaped, and has 10 small teeth on the distal end (or five pairs if you prefer). (Five or six teeth total in S. noctiflora, S. stellata, and S. vulgaris.) Evening campion evolved a dioecious life history (separate male and female plants) about 11 million years ago. (Other species in the genus have "perfect" flowers with both male and female organs present and functional in the flowers.) The evolution and genomic history of the sex-determining Y chromosome (XX = female, XY = male) has been of considerable interest for the light it shines on the evolution of Y chromosomes in both plants and animals (Moraga et al. 2025. Science 387:630–636; Akagi et al. 2025. Science 387:637–643).

Silene

Silene latifolia

evening campion [Blooms: May-Aug]

Royal catchfly's bright red flowers are restricted to the upper regions of the plant as clusters arising from the tips of stems. Individual flowers are 3/4-1" across, have an elongate (1"), narrow, cylindrical calyx with 10 longitudinal ridges, five narrow red or scarlet petals that flare from the tip of the calyx, and stamens with gray anthers that protrude well beyond the opening to the calyx. There are three corkscrew-shaped, threadlike styles that develop after the stamens have matured; like the stamens, they protrude well outside the calyx opening. The fruit is a 1/2" long capsule, open at the top, with 6-8 spreading teeth around the lip. Royal catchfly is hummingbird and butterfly pollinated.

Silene

Silene regia

royal catchfly [Blooms: Jul-Aug]

Starry campion's main stem ends in a panicle of flowers up to 8" long and 3-4" across; additional panicles may arise on the lateral stems on robust plants. Flowers occur in groups of 2-3 on the ends of long, slender branches; the flowers rest directly on short (1/4") pedicels. Individual flowers are 3/4" across. Each flower consists of a bell shaped, light green, fuzzy calyx nearly as broad as it is long with five broad, triangular teeth on its free end; five white petals with a narrow base and a "fringe" of 8-12 narrow lobes on their free ends; 10 stamens with slender white filaments that extend well outside the throat; and three white styles. The styles emerge from a large, green, globular ovary in the middle of the flower. After fertilization, the calyx gets broader (nearly triangular in profile) as the ovary expands into a spherical green ball; the fruit is brown, urn-shaped, and has six teeth on the distal end. The flowers tend to close in bright midday light. They are usually pollinated by moths and, to a lesser extent, bumblebees.

Silene

Silene stellata

starry campion [Blooms: Jun-Jul]

Water parsnip's upper stems end in 2-5" wide, flat-topped umbels of flowers with numerous (10-20) umbellets, each with 20-35 tiny (1/8" wide) flowers. At the base of the umbel are 6-10 narrow bracts that are curved down towards the stem. Each flower has a 3-5 mm long stalk; a short, light green calyx; five white, heart-shaped petals with incurved tips; five stamens that extend well outside the flower; and an ovary with two diverging styles. The fruits are 3 mm long, slightly laterally compressed, oblong, with strong ribbing; each fruit contains exactly two seeds.

Sium

Sium suave

water parsnip [Blooms: Jul-Aug]

Horsenettle's upper stems end in small clusters of 3/4" wide white or light violet flowers with wavy petal margins and hairy pedicels; clusters may also arise from leaf axils. Each flower has a green, hairy calyx with five lobes that taper gradually to sharp tips (typically slightly reflexed); five triangular petals that are fused at their bases; and five yellow, banana-shaped anthers 6-9 mm long surrounding a long, slim, light green style with a darker green, globular terminal stigma. After fertilization, the ovary expands into mature berries about 1/2" in diameter, initially green-striped, that look like yellow cherry tomatoes when mature; they are half enclosed in a papery derivative of the calyx.

Solanum

Solanum carolinense

horsenettle [Blooms: Jun-Aug]

Bittersweet nightshade flowers occur in small (6-12 flowers) clusters arising from the stems and leaf axils. Each flower is about 3/8" across consisting of a small green, purple, or brown calyx with five shallow, triangular lobes; five petals, purple with paired yellow or green spots at their bases, that flare or are reflected backwards over the base of the flower; five bright yellow anthers 4.5-6 mm long that are appressed to form a tight cylinder; and a single green, slender style closely surrounded by the anthers and protruding beyond them. The fruit is a 3/8-1/2" long, oval, tomato-like berry, initially green; mature berries are bright red. The foliage and fruit contain the alkaloid solanum and are toxic; fatalities are rare but have occurred. Horse nettle (S. carolinense) is similar to bittersweet nightshade but has numerous sharp bristles and spines on the stems and leaves that are lacking in bittersweet nightshade. Black nightshade (S. ptycanthum) is also similar but has black (rather than red) mature fruits and white (not purple) petals on the flowers.

Solanum

Solanum dulcamara

bittersweet nightshade [Blooms: May-Aug]

Black nightshade produces solitary umbels 3/4" long usually, from the axils of middle and upper leaves; the flower pedicels are about 3/8" long. Flowers are 1/4-3/8" across consisting of five sepals partially fused at the base of the flower; five white petals, green at their base, sometimes with purple highlights on the outside of the petal, and usually curved backwards; five anthers and their thick filaments appressed to form a tight, bright yellow cylinder with a yellowish-green stem; and a slender style running up the center of the appressed anthers to just emerge from the tip as a green stigma. The fruit is a 1/4-3/8" tomato-like berry, initially green; mature berries are black. The foliage and unripe fruit contain the alkaloid solanum and are toxic.

Solanum

Solanum ptychanthum

black nightshade [Blooms: Jul-Sep]

The axils of the middle and upper leaves of woodland goldenrod produce small clusters of 1-12 flowerheads; the stem tip may also develop a small (3" long, 1.5" across) panicle of flowerheads. Individual flowerheads are tiny (3 mm) consisting of 4-5 ray florets with yellow, oblong-elliptical "petals" and 3-6 disc florets with golden yellow, tubular corollas with five tiny lobes. At the base of each flowerhead are three overlapping series of light green, elongate-elliptical bracts (phyllaries). The fruit is a small, bullet-shaped seed 1-2 mm long with a tuft of white hairs 3-5 mm long. In Illinois, only woodland goldenrod and broad-leafed goldenrod (Solidago flexicaulis) produce clusters of flowerheads from the axils of the middle and upper leaves; however, the latter has coarsely serrated leaves with petioles and should be easy to distinguish from woodland goldenrod.

Solidago

Solidago caesia

woodland goldenrod [Blooms: Sep-Oct]

The tip of broad-leaved goldenrod's stem produces a cylindrical inflorescence (a raceme or a narrow panicle) 1.5-5" long and about a third as wide; smaller racemes (1/2-1.5" long, smaller than the leaves) arise from the axils of the upper leaves. Individual flowerheads are about 1/4" across with 3-4 yellow ray florets asymmetrically deployed around the flowerhead and 4-8 yellow disk florets. The base of the flowerhead is surrounded by 3-5 series of unequal, narrowly oblong, light green phyllaries; the outermost phyllaries are 1-2 mm long while the innermost are 3.7-4.7 mm long. Broad-leaved goldenrod prefers high-quality, moist, shaded woodlands. In Illinois, only broad-leaved goldenrod and woodland goldenrod (Solidago caesia) produce clusters of flowerheads from the axils of the middle and upper leaves. Broad-leaved goldenrod has unusually large flowers for a goldenrod and the ray florets are not evenly distributed around the flowerhead. In addition, woodland goldenrod has smooth or finely serrated leaf margins (rather than coarsely-toothed leaves) and no petioles (the leaves are sessile) — it should be easy to distinguish from broad-leaved goldenrod.

Solidago

Solidago flexicaulis

broad-leaved goldenrod [Blooms: Jul-Sep]

Early goldenrod's inflorescence is apical, a panicle of flowering stems that "often arch upward and outward like a fireworks display" (John Hilty, www.illinoiswildflowers.info). Individual flowerheads are about 1/4" across; they have 4-12 yellow ray florets, not all open at one time, and 8-15 yellow disk florets. The base of the flowerhead is surrounded by 3-4 series of overlapping, narrow, hairless, yellowish-green bracts (phyllaries) that together are 3-4 mm (1/16") long. The pedicels (flower stalks) are usually hairless, all attached on one side of the panicle's flowering branches and curving upward. The fruit is a cone-shaped dry seed 1-1.5 mm long with an attached tuft of light brown hairs 2.5-3.5 mm long. The combination of wing-like leaflets in the leaf axils, hairless stems and leaves, and an inflorescence whose flowering stems flare up and out is diagnostic for early goldenrod. Field goldenrod (Solidago nemoralis) is much the same size and general appearance, but has hairy stems and leaves, unlike early goldenrod.

Solidago

Solidago juncea

early goldenrod [Blooms: Jul/Aug-?]

The wand-shaped, nodding inflorescence of field goldenrod arises from the tip of the stem; it is 3-7" long and widest in the middle, tapering towards either end; the flowerheads are all on one side of the flower branches. Flowerheads are each 1/4" across consisting of 4-10 yellow ray florets and 3-10 yellow disk florets. The bracts (phyllaries) surrounding the base of the flowerhead are in three overlapping series; they are pale greenish yellow, covered in short, white hairs. The fruit is a dry seed 0.5-2 mm long with an attached tuft of light brown hairs. Field goldenrod can be distinguished from other goldenrods by (1) its diminutive size, (2) the inflorescence that nods to one size, (3) leaflets present in leaf axils (4) short, fine hairs on both leaves and stems, and (5) the grayish cast of the leaves.

Solidago

Solidago nemoralis

field goldenrod [Blooms: Aug-Oct]

Showy goldenrod's inflorescence is a showy, cylindrical panicle up to 12" long arising from the tip of the stem; the flowering stems are erect or curve upwards and the flowerheads occur on all sides of the flowering stems. (Unlike most goldenrods, where the flowering stems curve outward and downward and the flowerheads are on one side of the flowering stems.) Each flowerhead is about 1/4" across consisting of 4-10 large (for a goldenrod) pistillate ray florets (no stamens) and 6-16 perfect disk florets (both stamens and style). Behind the flowerhead are 3-4 series of overlapping bracts (phyllaries), each with a prominent midvein. The fruit is a 2 mm long seed with dark brown longitudinal grooves and a tuft of light brown hairs. Showy goldenrod is distinguished from other goldenrods by the character combination of: (1) stem leaf margins smooth (not toothed), (2) wing-like leaflets in axils of upper leaves, (3) the stems of the inflorescence erect or curve upward (not out and down), and (4) stems and leaves largely or completely hairless except in the inflorescence.

Solidago

Solidago speciosa

showy goldenrod [Blooms: Jul-Oct]

Elmleaf goldenrod's stem (and sometimes upper leaf axils) produces an open, airy inflorescence (a panicle) at its tip that may be a foot tall and wide with arching, widely-spreading branches. The flowerheads rest on very short stems (nearly sessile) along one side of the major branches, facing upward; on the opposite side of the branches are small (1") bracts. Both stems and branches in the inflorescence are covered with hairs. The flowerheads are 1/8-1/4" across with 3-6 yellow, pistillate ray florets (no stamens) and 4-7 yellow, perfect disk florets (both stamens and a style). Surrounding the base of the flowerheads are 16-18 bracts (phyllaries) in 2-3 overlapping series.

Solidago

Solidago ulmifolia

elmleaf goldenrod [Blooms: Jul-Oct]

Saltmarsh sand-spurry flowers consist of five elliptical green sepals, five white to pink petals slightly longer than the sepals, 2-5 stamens with bright yellow anthers, and three short (0.7 mm), thread-like styles and three stigmas. In the Great Lakes region, saltmarsh sand-spurry is widely present along roads where salt is used as a deicer. Some sources refer to this plant as Spergularia marina, but ITIS rejects that binomial; Spergularia salina is the accepted name.

Spergularia

Spergularia salina

saltmarsh sand-spurry [Blooms: May-Aug]

White meadowsweet's branches end in 2-6" long, oblong or pyramidal (1-4 times longer than wide) panicles of densely packed flowers that open from the top down. The flowers are about 1/4" across and are very similar to Eastern Meadowsweet (Spiraea latifolia) except for color (white rather than pink, although often pink as buds). Individual flowers consist of five triangular, light-green sepals; five white petals narrowest at their base, longer than the sepals; numerous (15-50) long, white stamens with white or pink anthers; and five light green or white pistils. The long stamens on the flowers give the flowerhead a fuzzy outline. The fruit is a cluster of 4-6 follicles, each containing one seed. When ripe, the top of the follicle splits, allowing the seed to fall out when the stem is shaken. Surrounding the pistils is a ring of pink, orange, or yellow tissue that marks the location of the nectaries. White meadowsweet prefers wet areas along the lagoons in Jackson Park.

Spiraea

Spiraea alba

white meadowsweet [Blooms: Jul-Sep]