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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 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 – ?]

Japanese tree lilac (aka, Japanese lilac) is an exotic shrub or tree that is native to Asia; it gets 20-30 feet tall and 15-25 feet wide. It may have multiple trunks. The bark on the trunk is shiny and reddish-brown (rather like cherry trees) with horizontally elongated lenticels (air pores). The leaves are 2-5.5" long and 1-3" wide, opposite, dark green, oval with a sharp tip and a rounded base with a 1/2-1" petiole, pinnate venation, and smooth margins. The inflorescences are 6-12" high panicles dense with creamy-white flowers. Individual flowers have a 1-2 mm long calyx; a 3-5 mm long cream-colored corolla with five stubby lobes (petals) and a four-lobed apex; five white stamens with yellow anthers widely spreading radially; and a single long white style bearing a club-like stigma. The fruits are 3/4" long dry capsules, initially green but turning reddish-brown or yellow with maturity. The capsule splits to release the two winged seeds.

Syringa

Syringa reticulata

Japanese tree lilac [Blooms: Jun-Jul]

The tips of the stems of goat's-rue give rise to 2-3" long racemes of buds and flowers. The unmistakable, bicolored pea-like flowers are about 1/2-3/4" wide and long, creamy white or yellowish on the vertical petal (the "standard") and rosy-pink on the lateral wings and the keel. (A total of five petals.) The flowers consist of a short, tubular calyx with five teeth, five petals in a pea-like configuration, 10 stamens (nine with fused filaments, one free from its midpoint) with small yellow anthers, and a single pistil with a tiny terminal stigma. Both stamens and pistil are enclosed by the keel. The seedpods are 1.5-3" long, cylindrical, slightly flattened beans spreading laterally from the flower spike; these, too, are (densely) silky-hairy. The seedpods are initially light green but turn brown with maturity. They split along the symmetry plane of the seedpod and the valves develop a spiral curl to release the seeds. Goat's-rue prefers sandy habitats. The long, woody roots contain rotenone, a compound that is toxic to fish and insects; it inhibits ATP production and disrupts mitochondrial function by blocking the electron transport chain. It would not be a good idea to suck on or ingest the roots of goat's-rue.

Tephrosia

Tephrosia virginiana

goat's-rue [Blooms: Jun-Jul]

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]

Immediately above the terminal stem leaves or leaflets of rue anemons is an umbel of one to six 1/2-1" flowers on 1.5" long pedicels. Each flower has 5-10 white or pinkish-white, petal-like sepals and a striking green center made of 1-16 pistils surrounded by 7-30 stamens with yellow anthers. There are no true petals. The fruit is a cluster of 5-15 strongly ribbed spindles about 8 mm long, pointed at both ends; each contains a single seed. Rue anemone prefers woodlands with dappled sunlight in the spring but tolerates shade in the summer months. The leaflets/leaves of rue anemone are similar to the leaflets of purple meadow-rue (Thalictrum dasycarpum), but you'll never confuse the two; purple meadow-rue blooms six weeks later and is seven feet taller than rue anemone.

Thalictrum

Thalictrum thalictroides

rue anemone [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]

Erect hedge-parsley's main stem and side stems give rise to umbels 1.5-2" across of 10-20 umbellets of flowers. Each flower is about 1/8" across consisting of five white petals (often markedly unequal in size), and a creamy white center surrounded by five pink to white stamens. The fruit is an 1/8" long oval covered in hooked hairs to aid in bur-like dispersal; it contains two seeds. (The fruit of common hedge-parsley (Torilis arvensis) has straight or only slightly curved hairs, not hooked, but the hairs are barbed.)

Torilis

Torilis japonica

erect hedge-parsley [Blooms: Jun-Jul]

Alsike clover is an exotic perennial native to Europe. Despite the scientific name ("hybridus"), it is not a hybrid. (Linnaeus thought it was a hybrid of red and white clover. It isn't.) The plant is 6-24" tall, with occasional branches along the stems. One- to three-inch-long flower stalks arising from the leaf axils terminate in a flowerhead 1/2-3/4" across; florets tend to be white on the top of the flowerhead and reddish-purple to pink on the bottom, but may all be reddish. Individual florets are 1/4" long with five petals in a pea-like bloom. They have a sharply pointed standard (the major vertical petal, perpendicular to the keel), two petals that make up the keel, and two lateral petals that flank the keel. Ten stamens and a single pistil are hidden inside the keel. Unlike red clover (T. pratense) and white clover (T. repens), there are no pale chevron-shaped markings on the leaflets.

Trifolium

Trifolium hybridum

alsike clover [Blooms: May-Jul]

White clover's hairless, leafless flower stalks are up to 3" long. They emerge directly from the horizontal stems and grow perpendicular to the ground, producing a single globular 3/4" wide flowerhead at their tips. The flowerheads are all white, consisting of 20-50 pea-like florets. The florets are tubular, consisting of a green calyx with five long, narrow teeth, and five white or pinkish-white petals (a standard, two petals making the keel, and a pair of lateral petals flanking the keel). White clover is similar to alsike clover (T. hybridum), but that species usually has some pink in the flowerheads and never has white chevrons on the leaflets.

Trifolium

Trifolium repens

white clover [Blooms: May-Jun]

Large-flowered trillium's single flower sits on a 1-3" long flower stalk; the flower is 3-4" across and leans to one side (but doesn't droop). The flower consists of three green, lance-shaped sepals with rounded bases, three white (pinkish in older flowers) petals with wavy edges, six stamens with golden yellow anthers, a central white ovary, and three styles fused basally but with separated, dull-yellow stigmas. The fruit is a six-angled, globose capsule, about 1/2" long, that is initially green but darkens as it matures; it splits open to release the seeds. The seeds carry an attached oily, fleshy food reward (an elaiosome) and are dispersed by ants which inadvertently deposit the seeds in their nests to take advantage of the reward. Large-flowered trillium prefers shady environments like woodlands and is slow to mature — it can take several years for a sprout to produce flowers.

Trillium

Trillium grandiflorum

large-flowered trillium [Blooms: Apr-May]

Slender stinging nettle plants are dioecious (unisexual) with male (staminate) and female (pistillate) flowers on separate plants. Flowers occur in knobby clusters (panicles) that arise from the leaf axils. Neither pistillate nor staminate flowers have any petals. Staminate flowers have four light green, identical sepals cupping four short stamens. Pistillate flowers also have four sepals but two sepals are narrowly lance-shaped, about a millimeter long, and free, alternating with two sepals that are 1.4-1.8 mm long and cupped around the ovary; styles are absent but the single stigma is long and feathery. The fruit is a flattened, oval to egg-shaped, seed less than 1/16" long. Stinging nettles (aka, tall nettle, slender stinging nettle) have a complicated biogeographic history. According to USDA Plants (https://plants.sc.egov.usda.gov/) and ITIS.gov, the subspecies "Urtica dioica gracilis" is native, while the subspecies "Urtica dioica dioica" is an exotic that is native to Europe and Asia. Thus, you may see "stinging nettle" listed as either "native" or "exotic." Both subspecies are perennials, and both occur in Illinois, although "gracilis" is most common; most features are the same for both subspecies. Wikipedia says these subspecies are actually separate species, an opinion based on a 2014 paper in Phytotaxa (162: 61-83) that analyzed molecular characters; Kew Garden's Plants of the World Online (https://powo.science.kew.org/) and iNaturalist also accept Urtica gracilis as a valid species. I've chosen to use "Urtica gracilis" here if only to avoid further proliferation of long scientific names in this presentation.

Urtica

Urtica gracilis

slender stinging nettle [Blooms: Jul-Aug]

Clusters of lowbush blueberry's flowers develop on the previous year's twigs. The flowers are about 1/4" long, urn- or bell-shaped, nodding, white, and waxy. The flowers contain a short, green calyx with five teeth; a short, tubular corolla that is pinkish white or white with five triangular, recurved lobes around its margin; ten stamens with reddish brown anthers recessed behind the margin of the corolla and clustered around the style; and a single style whose stigma extends right to the margin of the corolla. Fertilized flowers are replaced by approximately 8 mm diameter berries, initially green but turning dark blue with a whitish bloom as they mature. (I.e., they look — and taste — like blueberries.)

Vaccinium

Vaccinium angustifolium

lowbush blueberry [Blooms: May]

White vervain produces numerous 6" long, widely spaced flower spikes, each covered by tiny (1/8" wide) white flowers sparsely distributed along the length of the flower spike. Individual flowers consist of a hairy, tubular green calyx with five lance-like teeth and a curved, tubular corolla that abruptly flares into five short, rounded, brilliant-white lobes ("petals"). The throat of the flower is "bearded" (occluded by white filaments extending to the middle of the opening), hiding four stamens with greenish anthers, a green style, and a two-lobed stigma. The upper (more apical) two lobes of the corolla are slightly smaller than the other three (like prostrate vervain) and the tip of the lowermost lobe of the corolla is notched (like hoary vervain), but you're not likely to confuse white vervain with any other Verbena. The fruit is four oblong nutlets nestled in the remnants of the calyx.

Verbena

Verbena urticifolia

white vervain [Blooms: Jun-Sep]

ird's-eye speedwell (Veronica persica) flowers are solitary, arising from the axils of upper leaves on 1/2-3/4" long, hairy pedicels with a leaf-like bract at their bases. Individual flowers are about 8 mm across, consisting of a calyx with four lance-shaped sepals that are fused at their bases and are shorter than the corolla lobes, and a tubular corolla with four lobes ("petals") that are round to oval. The corolla is bluish toward the edges and whitish centrally, with dark blue lines radiating from the center. One of the four lobes is slightly smaller (and whiter) than the other three, so the flower is bilaterally symmetrical. A pistil with a single 2-3 mm long style arises from the center of the flower; two white stamens with dark blue anthers flank the pistil. Fertilized flowers produce a two-lobed fruit nestled in the remnants of the calyx, each lobe containing 5-11 small seeds; the fruit is a laterally compressed heart shaped capsule that is longer than tall with a distinct shallow V-shaped groove where the remnants of the style can be seen.

Veronica

Veronica persica

bird's-eye speedwell [Blooms: May]

Wayside speedwell's flowers are 1/4" across with a green, hairy calyx with four triangular lobes as long as the petals, projecting between them in the spaces between petals; a short corolla with four spreading lobes, three the same size (one on either side, blue to bluish-white with dark blue lines, and the third dark blue with blue-violet lines) and one about half as wide, pale blue or white with light blue lines. The blue lines function as nectar guides. The base of all four lobes is bright white, but the center of the flower is greenish. There are two white stamens with white anthers (backed by a dark blue "U" shape) and a single white pistil emerging from the throat of the corolla. The fruits are heart-shaped capsules with two chambers covered with glandular hairs, each containing 8-12 seeds. The flowers and leaves of wayside speedwell are similar to those of bird's-eye speedwell (Veronica persica), but the calyx lobes of bird's-eye speedwell do not project beyond the petals. There are 16 species of the genus Veronica reported from Illinois. I have only seen three (Veronica arvensis, Veronica polita, and Veronica serpyllifolia) in Jackson Park but, given their minute size and inconspicuousness, it seems likely that more remain to be found.

Veronica

Veronica polita

wayside speedwell [Blooms: Apr-Jun]

Thyme-leafed speedwell's upper stems host clusters (racemes) of flowers 2-7" long; flowers may either be opposite or alternate along the stem. Each flower is 1/8-1/4" across with a short (1/4"), slender petiole; at the base of the petiole is an oblong, hairless, leafy bract also about 1/4" long with smooth margins. (Thus, the flowers effectively arise from leaf axils.) Individual flowers consist of a green calyx with four triangular lobes shorter than the petals; a short corolla with four oval petal-like, lobes (the lowest one smaller than the other three); two stamens with purple or white anthers; and a green ovary with a single style. The lobes (petals) are white or pale blue, usually with dark blue lines radiating from the flower's center on the upper three lobes. The fruit is a laterally flattened, heart-shaped capsule 1/4" across with two chambers and a fringe of glandular hairs. When mature, the chambers split open, releasing 50-72 tiny seeds. There are 16 species of the genus Veronica reported from Illinois. I have only seen three (Veronica arvensis, Veronica polita, and Veronica serpyllifolia) in Jackson Park but, given their minute size and inconspicuousness, it seems likely that more remain to be found.

Veronica

Veronica serpyllifolia

thyme-leafed speedwell [Blooms: Apr-?]