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White avens blooms slightly later than rough avens (Geum laciniatum); it reaches about the same size (1.5-2.5' tall). The flowers are 1/2" diameter; they have five green sepals that are white-edged, pointed, and the same length or (usually) shorter than the petals; five white, rounded petals with a narrow attachment; and numerous (25-120) stamens surrounding a dome-shaped mass of green styles about a third the diameter of flower. The sepals initially lie under the petals but later become reflexed back parallel to the flower peduncle.The spherical fruit is covered with long, hooked spines (actually, persistant styles) that help the seeds stick to fur and clothing. White avens is distinguished from rough avens (G. lacinatum) by their flower stalks covered with short, fine hairs (rather than long, coarse hairs) and sepals that are shorter than the petals.

Geum

Geum canadense

white avens [Blooms: Jun-Jul]

Rough avens flowers are 1/2" wide, with five triangular green sepals longer than the petals, five cream or white, circular petals with narrow attachments, and numerous (25-120) stamens with (initially) cream-colored anthers distributed around a central gumdrop-shaped mound of green carpels with long styles. The fruit is more or less spheroid, 3/4" across, and covered with long, hooked spines (actually, persistant styles) that help the seeds attach to clothing and animal fur. Note that some sources identify this species as Geum virginianum, but G. virginianum is the cream avens according to the USDA Plants database; Hilty (ILW) lists G. virginianum as "restricted to southern Illinois". The two species are very similar, but G. lacinatum has very hairy stems and hairless receptacles and G. virginianum has smaller flowers (1/3") with cream-colored petals dwarfed by the sepals. Rough avens is distinguished from white avens (G. canadense, also found in Jackson Park) by petals that are shorter than the sepals and their very hairy flower stalks; rough avens also blooms earlier than whte avens.

Geum

Geum laciniatum

rough avens [Blooms: June]

Kentucky coffeetree produces a single 1.5-3' diameter trunk that, with its branches, can reach heights of 60-90'. The trunk bark is rough, scaly, gray or gray-brown; the bark on the branches is smoother, gray; the bark on the twigs is gray or brown with whitish lenticels. The leaves are alternate, bipinnate-compound, with 5-9 pairs of pinnate leaflets, each with 6-14 pairs of subleaflets. The entire compound leaf can be 3' long and 2' across, the largest leaf of any native tree in Illinois. Individual trees may produce only male flowers, only female flowers, or "perfect" flowers with both male and female organs flowers; the flowers develop as racemes on terminal branches fairly high in the crown shortly after the tree leafs out in the spring. Flowers are about 3/4" long and 1/2-5/8" across with a narrow, tubular calyx bearing five thick, narrow, sepals, and five narrow, greenish-white petals, slightly wider than the sepals, and a central column about as long as the petals that contains the reproductive organs. The male and perfect flowers have 10 fertile stamens (in alternating long/short pairs) in the central column; the female and perfect flowers have a fertile ovary and a single style contained in the central column. The calyx, sepals, and petals are all densely wooly with short hairs. The fruit is a stubby, reddish-brown seedpod 3-6" long and 1.5-2" across, somewhat flattened but less so than the fruits of honey or black locust. The seeds are brown, VERY hard, oval, and about a half inch long and across; they are toxic when raw but can be eaten after roasting.

Gymnocladus

Gymnocladus dioicus

Kentucky coffeetree [Blooms: May-Jun]

Although stickseed flowers are tiny (1/8"), they have the ususal complement of parts — a hairy green calyx with five long, narrow teeth that alternate with the petals; five rounded white (or light blue) petals (actually lobes of the corolla tube); five arching, scale-like structures surrounding the opening to the tube; five stamens largely hidden inside the corolla tube; and a four-lobed ovary with a short style, similarly hidden inside the corolla tube. The fruits are globular, <1/4" across, densely covered with hooked prickles; they are purportedly the most difficult of such "sticktights" to remove from clothing.

Hackelia

Hackelia virginiana

stickseed [Blooms: Jul-Aug]

Cow parsnip flowers are present in 6-8" wide, flat umbels (like Queen Anne's lace) that arise from the central stem or from leaf axils. Beneath each flower cluster are four or more needle-like, fuzzy green bracts; the bracts fall off after the fruit begins to form. Individual flowers are 1/4" across with five white petals that are notched at their tips; in flowers on the edge of an umbel, one petal is visibly larger than the other four. A somewhat lumpy, cream-colored, hairy ovary occupies the center of the flower from which arise two short styles; five stamens with pale yellow anthers arc laterally from under the ovary. Each fruit is heart-shaped, flattened, and contains two seeds.

Heracleum

Heracleum sphondylium

cow parsnip [Blooms: May/Jun-?]

Dame's rocket flowers occur in clusters (racemes) of up to 30. Each flower is 3/4-1" across and long, with a long, narrow, tubular, pinkish-green calyx composed of four long narrow sepals. The calyx opens through a narrow throat into four rounded, pinkish-purple (sometimes white) petals; the six pale yellow stamens and the multiple styles poke to various degrees out of the throat. Stems, leaves, pedicles, and the flower calyxes are all downy or hairy. The fruits are long (up to 4"), narrow, ascending, downy cylinders (siliques, typical of mustards) filled with flattened, oblong seeds. The flowers are very phlox-like, but phlox flowers have five petals, and dame's rocket only has four; phlox leaves are opposite on the stem (not alternate) and are narrower.

Hesperis

Hesperis matronalis

dame's rocket [Blooms: Apr-May]

Halberd-leaved rose-mallow is a striking wild hibiscus, usually found near water, whose stems can get 6' tall. Flowers arise from leaf axils, are trumpet-shaped, up to 5" across, with five rounded, partially overlapping white to pink petals; a central columnar reproductive structure covered in creamy-white stamens (with reddish-tan anthers) in whorls, and a terminal divided style with five recurved tips, each bearing a stigma shaped like the head of a pin. Behind the corolla is a green calyx with five lobes, and ~12 rod-like, curved, green bractlets below the calyx that taper to sharp points. The throat of the flower is a deep reddish-purple or rose pink. Seed pods form within the persistant sepals; the seed pod is divided into five sections filled with fuzzy brown seeds. The three-lobed (halberd-shaped) or five-lobed (maple leaf shaped) leaves distinguish this species from other rose-mallows. (Only swamp rose-mallow, Hibiscus moscheutos, also occurs in Jackson Park.)

Hibiscus

Hibiscus laevis

halberd-leaved rose-mallow [Blooms: Jul-Aug]

Flower-of-an-hour flowers are borne singly on hairy flower stalks that arise from the leaf axils; the flowers are 2" across, with five partially-overlapping petals that are white or pale yellow with deep purple bases. Sepals are pale green, translucent, and membranous with deep purple, hairy veins. The numerous stamens are borne on a "staminal column" that surrounds the base of the style; the filaments are maroon and the anthers are golden yellow. The single style is white where it rises above the staminal column and is divided at the tip into five knobby stigmas.

Hibiscus

Hibiscus trionum

flower-of-an-hour [Blooms: Jul-Sep]

Wild hydrangea canes produce a flat terminal panicle 3-6" across with 100-500 flowers of two kinds — small, fertile flowers filling most of the area and a few, sterile pseudo-flowers around the margin that are 3-4 times larger than the flowers in the center and seem to function only as an advertisement for pollinators. The central, fertile flowers are about 1/4" across with a green calyx made of five separate sepals; five greenish-white or cream petals about 1/8" long; 8-10 stamens with long filaments and oblong, white anthers; and a pistil bearing two styles with knob- or club-like stigmas. The sterile, outer pseudo-flowers have 3-4 fused petal-like, white bracts (or sepals; sources differ) with a central structures that visually is reminiscent of stamens or styles; the pseudo-flowers persist long after the inner flowers have been fertilized and have produced a two compartment seed pod that is ribbed and bears a pair of tiny horns (the styles) on its upper end. Wild hydrangea is relatively rare in northern Illinois; in Jackson Park it prefers wooded area by walking paths.

Hydrangea

Hydrangea arborescens

wild hydrangea [Blooms: Jun-Aug]

Panicled hydrangea (Hydrangea paniculata) is an exotic perennial native to China and Japan that may grow as either a shrub or a tree. Neither Natureserve Explorer nor the USDA Plants database acknowledge the presence of panicled hydrangea in Illinois, but the Morton Arboretum and the University of Illinois Extension both explicitly do. Panicled hydrangea is widely sold in nurseries; commercial cultivars reach 10-15 feet high and wide. It definitely occurs in Jackson Park, near our native species — wild hydrangea (Hydrangea arborescens) — but I have not seen it in direct competition with wild hydrangea. The inflorescence is a conical panicle typically covered with two types of flowers — large, nominally-sterile flowers and smaller, bisexual flowers — scattered across the surface of the panicle. The "sterile" flowers are white or greenish white with typically 4-5 (3 in Jackson Park) elliptical to round lobes (actually sepals) 1/2-1" long and 1/3-2/3" across (8-15 mm). In Jackson Park, at least half the nominally sterile flowers bear a small, budlike structure in their center that exhibits three lobes (petals?), have 3-6 distinct stamens with small anthers, and a two-lobed central structure that is probably a reduced pistil. It is not clear whether either the pistils or stamens are functional. The bisexual flowers usually have five tiny (less than 1 mm long and wide) sepals, five petals 3-4 mm long and 0.1-0.3 mm wide (which often fall off the flower), 2-5 mm long stamens, and an ovary with 2-4 spreading styles (two in Jackson Park specimens) that are 2-3.5 mm long and are fused at their bases. After fertilization, the petals and stamens wither and fall off; the remainder of the flower forms an oblong, 3-5 mm long, seed capsule. The easiest ways to tell panicled hydrangea (H. paniculata) from wild hydrangea (H. arborescens) is: (1) the inflorescence is conical or pyramid-shaped in panicled hydrangea but a flat disc or shallow dome in wild hydrangea, and (2) the showy, "sterile" flowers in panicled hydrangea are scattered evenly across the surface of the inflorescence in panicled hydrangea, but are restricted to the margins of the inflorescence of wild hydrangea (rather like the inflorescence of the much more common but unrelated American cranberry, Viburnum opulus var. americanum). Wild hydrangea is much more common than panicled hydrangea in Jackson Park.

Hydrangea

Hydrangea paniculata

panicled hydrangea [Blooms: Jul]

Virginia waterleaf stems are variable in color (green, reddish-green, or reddish-brown) and up to 2' tall. Each upper stem has at their tips one or two clusters (cymes) of 8-20 flowers that is 1-2" in diameter on a 4" stalk (peduncle); the central flower opens first. Individual flowers are 1/4-1/2" long, roughly bell-shaped, white, pink, or light violet in color. Flowers have a green, hairy calyx with five long, narrow teeth fringed with widely-spaced, stout hairs; a tubular corolla with five equal lobes at the open end; five stamens covered with long hairs along their lower half, with anthers initially yellow that later turn dark brown; and a single lavender style with a white, bifurcated tip. Both the stamens and the style are 30-50% longer than the corolla lobes and extend well beyond their edges.

Hydrophyllum

Hydrophyllum virginianum

Virginia waterleaf [Blooms: May]

Small white morning glory is a vine 3-8' long, covered in scattered white hairs. The flowers are much smaller (1" long and 3/4" across) than most other Jackson Park morning glories, pentagonal rather than circular in outline, white, and shallowly lobed. The flowers consist of five lance-like sepals about 4 mm long, the funnel-like corolla, five stamens with a white filament and pinkish-purple anthers, and a single style with a knobby or bifurcated stigma. Fertilized flowers produce a spherical, hairy seed capsule about 1/2" in diameter nestled in the five sepals. Unlike the other two morning glories in Jackson Park, small white morning glory is native, but uncommon in northern Illinois.

Ipomoea

Ipomoea lacunosa

small white morning-glory [Blooms: Aug-Sep]

Wild sweet potato is a twining vine that can reach 20-30' long, completely covering the adjacent vegetation. The flowers are funnel-shaped with five shallow lobes, 2.5-3" across, white with a reddish-purple or rosy throat. There are five stamens of different lengths with filaments up to an inch long and whitish-pink anthers; there is a single whitish style with a two-lobed stigma. The flowers tend to bloom early in the day, later if cloudy. Individual flowers are short lived but this plant is a prodigious producer of blooms; it is the largest morning glory in Jackson Park. The "sweet potato" is a modified root up to 20" long and weighing 30 pounds; it is edible, but only barely.

Ipomoea

Ipomoea pandurata

wild sweet-potato [Blooms: Jun-Aug]

Common morning glory is a vine up to 10' long with alternate, heart-shaped (never lobed), smooth-margined, almost as wide as long. The stem is green or reddish-purple, covered with long hairs; it twines around adjacent vegetation and objects. Cymes of 1-5 flowers arise from some leaf axils; they sit at the tip of about 4" long pedicels. The flowers are 2-3.5" wide, funnel-shaped, usually deep purple or pink, less commonly blue or white, a single style with a three-lobed stigma, and five stamens. Sepals are relatively short, hairy, and triangular unlike ivy-leaved morning glory (I. hederacea), where the sepals are long and narrow. Other morning glories (Ipomoea sp.) usually have lobed leaves; the superficially-similar bindweeds usually have arrowhead-shaped leaves, not heart-shaped. Common morning glory has sepals that are short and triangular, unlike ivy-leaved morning glory where the sepals are relatively very long and narrow. Common morning glory is native to Mexico; it was introduced to England by 1621, then introduced from England to North America around 1700 as an ornamental (Fang et al., 2013), where it rapidly escaped cultivation.

Ipomoea

Ipomoea purpurea

common morning-glory [Blooms: Aug-Sep]

American water-willow produces long (up to 6") peduncles from some of the upper leaf axils that have clusters of flowers on their tips. Individual flowers are 3/4" across with a short, tubular, 1/4" long, green calyx with five teeth and a tubular corolla with four lobes — an upper lobe with a shallow V-notch, two widely spreading lateral lobes, and one lower lobe at right angles to the other three. Both the lateral and lower lobes are folded downward along their midlines, producing a U-shaped cross-section. All of the lobes are white or pale purple with a darker splotch on the end of the upper lobe and dark purple spots along the midline of the lower lobe and at the base of the lateral lobes. There are two stamens, each with a dark brown pair of anthers posed in front of the upper corolla lobe and a single, narrow, white style running along the midline off the upper lobe and protruding beyond its upper boundary.

Justicia

Justicia americana

American water-willow [Blooms: Jun-Aug]

Wood nettle plants may be either monoecious (separate male and female flowers on the same plants) or unisexual (only male or only female flowers). Male flowers are produced from branching cymes 4" long that arise from the leaf axils; female flower are produced from branching cymes, also 4" long, localized near the apex of the stem. Male flowers are small (1/8" across), consisting of five narrow, greenish-white sepals and five stamens; there are no petals but there is a vestigial pistil. Female flowers are about the same size (1/8" across) with four green sepals (two larger, two smaller) that look like tiny leaves with undulating edges and an ovary with a long, white, vertically-oriented J-shaped style that tapers to a point. The female flowers are wind-pollinated. The fruit is circular in outline but very flattened, green turning black with maturation, on a short winged stalk; the remains of the style are attached at the free end of the fruit.

Laportea

Laportea canadensis

wood nettle [Blooms: Aug-Sep]

Field peppergrass tems produce racemes of flowers near their apex; flowers near the top of the raceme are the youngest with older flowers (and later seed pods) further down the inflorescence. The flowers have a calyx of green or purple-green, lance-like sepals, four white, spoon-shaped petals, six stamens, and a single style. The fruits are flattened pods oval in outline with the remnants of the style protruding from a notch in the end (rather like field pennycress, Thlaspi arvense); each seedpod contains two seeds. This is an easy plant to overlook if only because it look like the weed that it is.

Lepidium

Lepidium campestre

field peppergrass [Blooms: May-?]

Peppergrass (aka, Virginia pepperweed) is a weedy, 1.5' tall, rather bushy plant. The flower spikes (racemes) are 2-4" long with tiny (<1/8") white apical flowers forming a larger inflorescence. The flowers have four oblong green or tan sepals with a white edge, half the length of the petals, alternating with four white, triangular petals. There are two stamens with yellow anthers and a stubby (0.2 mm tall) style on a green ovary. Below the flowers, the flower spike is covered with 1/8" wide seedpods on (relatively) long stalks, reminiscent of a bottlebrush; the seedpods are oval with an apical notch (much like half-sized versions of field pennycress (Thlaspi arvense) seedpods) containing two seeds. This species is native to the U.S. The stubby cylindrical inflorescences are and the triangular petals alternating with shorter sepals are diagnostic and distinguish pepper grass from field peppergrass (Lepidium campestre).

Lepidium

Lepidium virginicum

peppergrass [Blooms: Oct-Nov]