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Common sowthistle flowerheads are less than 3/4" in diameter and look very dandelion-like; they open in the morning and close by noon. Each flowerhead consists of numerous (80-250) yellow ray florets; disc florets are absent.

Sonchus

Sonchus oleraceus

prickly sowthistle [Blooms: Jun-Oct]

The central stem of giant bur-reed produces an inflorescence at its tip with 1-6 female flowers in the lower parts of each branch of the inflorescence and up to 20 male flowers in the upper parts. (Male and female flowers are separate and distinct.) Male (staminate) flowerheads look like a fireworks-burst of white filaments and yellow-brown anthers; individual florets are densely packed, each with five stamens with white filaments and a yellow to brown anther. The female flowerheads are greenish and "prickly" with prominent green cones (the female florets) covering the surface; each pistillate floret has a basal green ovary covered with scale-like tepals with dark tips and an apical white style bearing two white stigmas. Giant bur-reed is wind pollinated. In fruiting flowerheads, the stigmas turn dark and wither but do not drop off; the florets elongate and widen, turning brown as the fruits on the seedhead ripen. The fruit is a brown seed 5-10 mm long and nearly as wide, shaped like an inverted pyramid that abruptly narrows to a 2-4 mm long apical beak (the style remnant). Giant bur-reed is superficially sedge-like but instead is more closely related to cattails. Giant bur-reed prefers wet conditions (up to a foot of water) with minimal waves and gentle currents.

Symphytum

Sparganium eurycarpum

giant bur-reed [Blooms: May-Jul]

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]

The leafy stems of Drummond's aster end in a panicle 1/2-2 feet long and half as wide bearing white flowerheads with yellow or maroon centers. Individual flowerheads are 1/2-3/4" across; they have 10-15 ray florets and 13-15 disk florets. The ray florets have bright blue, purple, or white tubular corollas and white rays (petals); the disk florets have cream to yellow tubular corollas, turning deep purple or reddish purple with age. Both disk florets and ray florets are perfect with bright yellow anthers on the stamens and white, bifurcated styles, but the ray florets are sterile. The base of the flowerhead is covered with 4-5 series of overlapping, light green phyllaries (bracts). Each phyllary is 4-6 mm long, light green, with a diamond-shaped patch of dark green near their tip. The fruit is a dry seed with a tuft of attached brown to white hairs. Note that the leaf petioles are winged and the leaves are broad and toothed. The upper surface of the leaf is rough (unlike Short's aster, the most common species in Jackson Park that you might confuse with Drummond's aster). The even pubescence (down-like hairs) on the underside of the leaves and along the stems distinguishes Drummonds aster from the other look-alike aster in Jackson Park, white arrowleaf aster (Symphyotrichum urophyllum). The phyllary pigmentation is also distinctive.

Symphyotrichum

Symphyotrichum drummondii

Drummond's aster [Blooms: Sep – ?]

Each heath aster flowerhead is 1/3-1/2" across with 8-20 ray florets (usually 12) and 6-12 disk florets. The ray florets are sterile; the disk florets are perfect and fertile. The phyllaries occur in 3-4 series on the back of the flowerhead; they are blunt-tipped, often recurved away from the flowerhead, with a distinct apical spine. Also note the spines at the tips of the numerous needle-like bracts on the flower stems. (Note: hairy aster (S. pilosum) also has such apical spines but has larger flowers, rolled, needle-like phyllaries with a smaller spine, and spreading hairs on the stems.)

Symphyotrichum

Symphyotrichum ericoides

heath aster [Blooms: Sep – Nov]

Smooth blue aster's central stem produces a one-half to one foot long (and half as wide) panicle of flowerheads with stiff, ascending branches covered with small, leafy bracts. Smaller panicles may arise from some lateral upper stems and the axils of the upper leaves. Individual flowerheads are 0.5-1" wide, consisting of 15-30 light lavender or light blue-violet ray florets and 19-33 disk florets that are initially a whitish yellow but change to purplish red over time. The phyllaries that cover the back of the flowerhead are arranged in 4-6 overlapping series and have a diamond-shaped, green tip, often with a spot of red at the very tip. The fruit is a brown, dry seed, flattened, narrowly cone-shaped with 4-5 longitudinal ribs, 2-4 mm long with a tuft of brown hair. The most useful character to distinguish smooth blue aster from other asters is the lack of hairs on its stems and leaves; the uniformly clasping leaves (no petioles) is another useful character. For example, the superficially similar skyblue aster (Symphyotrichum oolentangiense) has lower and middle leaves with distinct petioles and none of its leaves actually clasp the stem.

Symphyotrichum

Symphyotrichum laeve

smooth blue aster [Blooms: Aug – Sep]

Panicled aster's central stem gives rise to an 8" long panicle (4" wide) of flowerheads; panicles may also arise form lateral stems and the axils of upper leaves. The panicle branches tend to be hairier and more often grooved than the stems; there are bracts (1.5" long, 8 mm wide) at the base of the panicle branches and the base of the flowerhead stalks. Individual flowerheads are 1/2-3/4" across with 1.5" long flower stalks (peduncles). Flowerheads have 20-40 white (less often blue or violet), pistillate (no stamens) ray florets, and an equal number of perfect (pistils and stamens) disc florets that are initially yellow, turning red orange with age. Phyllaries (bracts) cover the back of the flowerhead in 3-6 overlapping layers; the phyllaries are narrow, green with paler bases, appressed or slightly spreading, with the outer layer shorter than the inner. The fruit is a 1.5-2 mm long gray seed with a tuft of dull white or yellowish hairs. It's easy to confuse panicled aster with other asters that have small, white flowerheads. Look for: (1) leaves with wedge-shaped (not rounded or heart-shaped) bases, (2) mature leaves hairless on both sides, (3) stems with lines of white hairs, and (4) flowerheads with at least 20 ray florets. (Count the "petals.")

Symphyotrichum

Symphyotrichum lanceolatum

panicled aster [Blooms: Aug – Oct]

Panicles of flowerheads up to 10" long and 6" across arise from the upper stems (and some side stems) of calico asters. Individual flowerheads are about 1/3" (8 mm) across, typically consisting of 8-15 white ray florets and 8-16 cream or light-yellow disc florets turning brown or reddish purple with age. The flowerheads sit on a 1/3" long, hairy flower stalk (peduncle) with a few leaf-like bracts along the peduncle. The base of the flowerhead is covered by phyllaries (bracts) in 3-4 overlapping layers; the phyllaries are sparsely hairy, appressed or slightly spreading, with a darker green lance- or diamond-shaped tip. The fruits are fuzzy dry seeds with a tuft of white hairs. Calico asters are distinguished from other small, white asters by: (1) very small flowerhead (<1/2"), (2) relatively few (9-16) ray florets/petals, (3) creamy white or pale (not bright) yellow disk florets, (4) lance-elliptic leaves with hairs only on the midvein, (5) stems with lines of soft, white hairs. Other asters (e.g., panicled aster) will have one or more of these characters, but not the full suite.

Symphyotrichum

Symphyotrichum lateriflorum

calico aster [Blooms: Sep – ?]

Clusters of flowerheads occur at the tips of the upper stems of New England asters. Individual flowerheads are large (1.5" across) with 50-75 (!) purple, lavender, or pink ray florets; the 50-110 disk florets are yellow or gold, turning reddish purple with age. A healthy New England aster with two or three dozen flowerheads is an impressive sight indeed. Phyllaries surround the back of the flowerhead in 3-5 layers. They are green or purple-tinged, very narrow but robust, widely spreading or reflexed, with the outermost layer of phyllaries covered with short glandular hairs. The fruit is a longitudinally ribbed, quite hairy, dry seed with a tuft of long, light brown hairs. The large, showy flowerheads with very large numbers of ray florets (petals) can't be confused with any other aster in Jackson Park.

Symphyotrichum

Symphyotrichum novae-angliae

New England aster [Blooms: Aug – Nov]

Skyblue aster's central stem terminates in a 6-18" long panicle of flowerheads; the panicle is twice as long as wide. The panicle has a central stalk (rachis), several primary branches and numerous secondary (off the primary) and tertiary (off the secondary) branches that end in flowerheads. The branches have scale-like, 3/4" long leafy bracts spaced along their lengths. Individual flowerheads are 1/2-3/4" across with 10-25 lavender or pale blue ray florets and 20-25 disk florets. The disk florets are initially yellow, turning reddish-purple with age; they seem to me to be unusually large for an aster. The phyllaries (bracts) surrounding the base of the flowerhead are small (2 mm) and tightly appressed, each with a diamond-shaped green tip and often with a spot of blue-purple at the very tip. The fruits are bullet-shaped, 1.5-2mm long dry seeds, purplish brown, with a tuft of hairs. Skyblue aster is similar to smooth blue aster (S. laeve), but that species has sessile leaves; sky blue aster has petioles on the lower and middle leaves, only the upper leaves are sessile. Skyblue aster is also similar to Short's aster (Symphyotrichum shortii), but the latter has upper leaves with a heart-shaped base rather than smoothly tapering to a sessile attachment as in skyblue aster. Generally, skyblue aster is most easily identified by the long, narrow, arrowhead-shaped lower leaves that feel like fine sandpaper on both surfaces.

Symphyotrichum

Symphyotrichum oolentangiense

skyblue aster [Blooms: Sep – Oct]

The upper stems of hairy aster give rise to 2 foot long, 1.25 foot wide panicles with a central rachis that produces spreading or ascending primary branches and smaller secondary branches that bear the flowerheads. Each flowerhead is 1/2-3/4" across with 15-35 white ray florets and 20-40 yellow disk florets that turn reddish purple or brown with age. The bracts (phyllaries) that surround the base of the flowerhead are present in 4-5 layers; they are 3 mm long and light green with a long, darker green tip. The edges of the phyllaries are often rolled under and thus may appear needle-like. The phyllaries and the bracts attached to the panicle branches both have a tiny spine at their tip. (Note: heath aster (S. ericoides) also has such spines but has smaller flowerheads, broad, blunt phyllaries with a larger spine, and the hairs on the stems are either appressed to the stem or are ascending.) The fruits are 1-1.15 mm long, tan colored, dry seeds with 3-4 longitudinal ribs and a tuft of white hairs. After blooming is completed, rosettes of 3" long, 1" wide, spoon-shaped basal leaves develop and persist through the winter into the spring, but wither away before blooming begins again.

Symphyotrichum

Symphyotrichum pilosum

hairy aster [Blooms: Aug – Nov]

The panicles of Short's aster's flowerheads are up to 18" long and 8" across; the panicles arise from the tips of the central stem and the upper lateral branches. The flowering branches are long, widely spreading or arching, and covered with small, leaf-like bracts and stiff hairs. Individual flowerheads are 3/4-1" across. Flowerheads consist of 10-20 lavender or pale blue-violet (rarely white) ray florets and 15-23 disk florets, initially yellow but becoming reddish purple over time. The phyllaries that surround the base of the flowerheads are covered with stiff, white appressed hairs, are whitish or light green with a diagnostic dark green, diamond-shaped tip, and sometimes also with a dark green medial vein. The fruits are 2-3 mm long, oblong-shaped, with a tuft of light brown hairs at one end. The indented bases of the lower and middle leaves, the slender, wingless petiole, the hairless leaves, and the phyllaries with dark green apical diamonds together are good indicators of Short's aster. Short's aster is the commonest aster in bloom in Jackson Park in early autumn; later in the autumn it is overtaken in numbers (or at least visual impact) by New England asters.

Symphyotrichum

Symphyotrichum shortii

Short's aster [Blooms: Aug – Nov]

The upper stems and branches (some arising from upper leaf axils) of white arrowleaf aster terminate in 6-18" long panicles of flowerheads; the panicles are 2-3 times longer than wide. Each flowerhead is 1/2-3/4" across with 8-15 pistillate, white (rarely pale lavender) ray florets and 10-15 perfect (both stamens and styles present) disk florets. The disc florets are initially yellow but turn pink or light purple with age such that the flowerheads with yellow disk florets are often in the minority on the plant. The individual disk florets strike me as being larger than on many asters. The phyllaries (bracts) covering the base of the flowerhead are narrowly lance-shaped, usually hairless, dark green in the middle tapering to narrow, stiff, green to purplish tips. The fruits are 2 mm long, purplish-brown dry seeds with longitudinal ribs and a tuft of hairs at one end. White arrowleaf aster is similar to Drummond's aster (Symphyotrichum drummondii) but is less hairy and has distinctly different phyllaries. Among asters with white flowerheads, only white arrowleaf aster has heart-shaped leaves. (Other asters with heart-shaped leaves typically have blue to violet flowers.)

Symphyotrichum

Symphyotrichum urophyllum

white arrowleaf aster [Blooms: Aug/Sep – ?]

Some upper stems produce compound umbels at their tips made of tiny, yellow flowers; the umbels are very open (they remind me of a fireworks burst), up to 4-7" across with 12-15 umbellets of about a dozen flowers. Individual flowers are about 1/8" across with five tightly furled, yellow petals; five stamens emerging from between the incurled petals and widely spreading with pale yellow anthers; and two styles. Sepals are absent. The flowers tend to be either pistillate (stamens reduced or absent) or staminate (styles reduced or absent), but a few perfect flowers occur. Yellow pimpernel prefers dry habitats on a slope at the edge of woods.

Taenidia

Taenidia integerrima

Yellow pimpernel [Blooms: May-?]

Dandelion plants produce one to several slender flowering stalks from the center of the basal leaf rosette. Each floral stalk is cylindrical, hollow, and light green (often with a light reddish green base); there is a single 1-2" wide, yellow flowerhead at the apex of each stalk. The floral stalk may be covered with cobwebby hairs. Each flowerhead has 150-200 yellow ray florets spreading outward toward the periphery of the flowerhead; disc florets are absent. The ray flowers have a flat, strap-like "petal" with a series of tiny teeth at its distal end; the anthers sheath the surface of the style, which protrudes from the distal end of the tube of fused anthers as a bifurcated stigma. The base of the flowerhead is covered by two layers of green bracts; the inner layer of bracts forms a cylindrical tube around the ovaries of the ray florets, while the outer layer of bracts is sharply reflexed back along the floral stalk. The fruit is a narrow, cylindrical seed 3-4 mm long with 5-10 longitudinal ribs on its surface; the seed is attached by a 7-9 mm long beak (stalk) to a parachute-like tuft of white hairs. The airy seedheads are formally known as "clocks" in both British and American English (before the seeds are released by an errant breeze or child). Dandelion seeds can remain viable in the soil for up to nine years.

Taraxacum

Taraxacum officinale

dandelion [Blooms: Mar-Jun]

Purple meadow-rue is a native perennial that is listed as "vulnerable" in Illinois. The species is found in most of the lower 48 states in the U.S. but is notably absent from states on the Atlantic and Pacific coasts (however, it is present along the Gulf of Mexico). Purple meadow-rue is dioecious — some plants produce only staminate (male) flowers, each with around a dozen stamens; other plants bear only pistillate (female) flowers, each with about ten pistils. The male flowers are the showier of the two. Petals are absent (the plant is wind-pollinated). Both the narrow, whitish-grey, thread-like pistils and the yellow-green stamens (with pale yellow anthers) droop from 4-5 light green sepals (that may drop off). Fertilized female flowers develop a single, spindle-shaped fruit that is 1/4" long, elongated, sharply pointed with a remnant style, 4-6 raised ribs, and slightly concave along one side. The fruit is initially green, turning brown with maturity. Early meadow-rue (Thalictrum dioicum) is similar to purple meadow-rue but has light purplish-green stems and leaves with 3-9 (typically five) rounded lobes and long petioles on the upper leaves.

Thalictrum

Thalictrum dasycarpum

purple meadow-rue [Blooms: May-Jun]

Early meadow-rue's main stem terminates in a panicle up to a foot long and wide; each branch in the panicle has a corymb of about five flowers at its tip. Early meadow-rue is dioecious — some plants produce only staminate (male) flowers, each with 10+ stamens; other plants bear only pistillate (female) flowers, each with up to 15 pistils. Both male and female flowers droop from their stems, but the male flowers have a longer droop than do the female flowers. Both male and female flowers are about 1/2" long and 1/4" across with 4-5 pale green sepals with white margins (which often fall off). Neither male nor female flowers have petals; pollination is via the wind. Fertilized female flowers produce ellipsoid, dry seeds that are pointed at both ends; the surface bears strong ribbing. Early meadow-rue prefers shady woodlands. It has more lobes on its leaves (usually 3-5), and the lobes are more rounded than purple meadow-rue (Thalictrum dasycarpum), the other Thalictrum species in Jackson Park, does (2-3 pointed lobes).

Thalictrum

Thalictrum dioicum

early meadow-rue [Blooms: Apr-May]

Field pennycress's central stem and the upper side stems produce racemes of flowers at their tips. The flowers bloom at the tip of the raceme, which continues to elongate to 3-8" long and to produce new buds; the prominent, disk-shaped fruits develop lower on the raceme. Individual flowers are about 1/8-1/4" across on a 1/2" pedicel; there are four green sepals with whitish edges, four white, oval petals, six yellowish-green stamens (three on each side of the flattened ovary), and a single short style. The fruit is a 1/2" wide flattened, winged disc with a distinct U-shaped notch at the apex; the fruits are borne on the flower pedicels, which spread perpendicular to the stem. Each seedpod has two compartments, each compartment containing several dark brown seeds. Other mustards have long, cylindrical seedpods; the nearly-circular seedpod of field pennycress is unique among Jackson Park mustards. Young field pennycress plants are edible but become very bitter at flowering. Cows that feed on field pennycress produce "tainted" milk that tastes like garlic.

Thlaspi

Thlaspi arvense

field pennycress [Blooms: Apr-Jun]