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Galinsoga (aka, Peruvian daisy or shaggy soldier) flowerheads are small (1/4" across) with 4-8 (usually five) widely separated 2.5 mm long, white ray florets with three teeth at their tips. The 15-35 disc florets are yellow. Both ray and disc florets are fertile; the ray florets are pistillate while the disc florets are perfect (both pistils and stamens). The fruit (a cypsela) consists of a black, conical seed suspended beneath about five off-white, papery, fringed scales that act as a parachute. A poisonous plant (Tridax procumbens) with nearly identical flowers (but distinctly different leaves) is (luckily) restricted to FL and TX in the U.S. so not likely to show up in Jackson Park. The name Galinsoga ciliata, sometimes still used for Galinsoga quadriradiata, is invalid (ITIS); according to the USDA Plants database, C. ciliata has been superceded by either G. quadriradiata or G. urticifolia.

Galinsoga

Galinsoga quadriradiata

galinsoga [Blooms: Jun-Oct]

Cleavers' flowers are tiny (2-3 mm across), star-shaped, with two green carpels covered with hooked hairs joined at the base of the flower; four white, pointed petals; four stamens; and two styles. The fruit is a spherical capsule formed from the carpels, covered with stiff, hooked hairs, each carpel containing a single seed.

Galium

Galium aparine

cleavers [Blooms: Apr/May-?]

Ground ivy flowers are 1/2" long and arise from the leaf axils; they are purplish, trumpet shaped, with a notched upper and lower (the largest) lobe and two small side lobes; the "throat" of the lower lobe is hairy. There are four stamens (two long, two short) with purple to blue anthers, and a single pistil with a bifurcated purple style. The corolla of the flowers is cupped by a hairy, green, tubular calyx that has 15 ridges distributed around the calyx running longitudinally, and five triangular teeth at the apex of the calyx. The fruit is a nutlet that nestles in the calyx.

Glechoma

Glechoma hederacea

ground ivy [Blooms: Apr-May]

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]

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]

Black walnut has separate male and female flowers on the same tree (often the same branch). The male florets occur on 3-6" long, dangling, green, cylindrical catkins that arise from the leaf axils of one-year-old branchlets; the florets are 1/8" across and are comprised of a short, tubular calyx with 2-6 lobes and 15-40 stamens with greenish-yellow or purplish anthers. The female florets occur in groups of 2-5 on short spikes that arise from the tips of the current year's new branchlets; these florets are also about 1/8" across but are comprised of a short, tubular calyx with four lobes, a stout, green ovary covered with sticky hairs, and a pair of stout, bushy styles with red-tinged stigmas. The female florets are wind pollinated; the trees are self-fertile if cross-pollination does not occur. Fertilized female florets develop into globoid nuts about 2.5" long and 2" across that initially retain the styles; the nuts are solitary or in pairs. The thick husk turns from green to yellowish-brown to black as the fruit matures. The nuts cannot germinate unless they are exposed to 90-120 days of cold winter temperatures.

Juglans

Juglans nigra

black walnut [Blooms: May?-Jun]

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]

American bugleweed flowers form in whorls of the axils of the middle and upper leaves. Individual flowers are 1/8" across, white with pinkish-purple spots, with a calyx about as long as floral tube with five teeth; the distal end of the short tubular corolla has five sharply-pointed, narrowly-triangular lobes. The two stamens with purple anthers and single style project well outside the mouth of the corolla. The fruits are four, flat-topped nutlets that form in the cup of the calyx. The deep, narrow lobes of the lower leaves are a characteristic of this species; they are not present in the other Lycopus species in Jackson Park.

Lycopus

Lycopus americanus

American bugleweed [Blooms: Jul-Sep]

Gypsywort (aka, European bugleweed) is another species native to Europe and Asia. How it came to the New World is unknown, but it has a long history in the botanical literature in Europe (back to the sixteenth century). It strongly prefers wetlands and can often be found in muds. The stem can be as much as 2.5' tall, usually unbranched, light- or yellowish-green, square in section, hairy, and finely grooved. Flowers occur in whorls in the axils of the upper leaves. Each flower is 1/8" across consisting of a green calyx with 4-5 teeth, each longer than the calyx tube, giving the mass of flowers a bristly appearance; a white tubular corolla with four apical lobes, usually with a few pink or purple spots on the lower lip; two stamens; and a style with a bifurcated tip (which can be difficult to see). The fruits are four, concave-topped nutlets cupped in the calyx. This species is known to hybridize with American bugleweed (Lycopus americanus). The medicinal properties of gypsywort are quite controversial; resist the urge to nibble.

Lycopus

Lycopus europaeus

gypsywort [Blooms: Aug-Sep]

Pineapple-weed, unlike it's cousin wild chamomile (Matricaria chamomilla), is probably native to North America, specifically the Pacific Northwest, but has spread widely both here and in Europe. It is a small plant (up to 12" tall); the stems branch frequently. Flowerheads sit on 1/2-1.5" long flower stalks that arise from leaf axils. Each flowerhead is a gumdrop-shaped or conical mass about 8 mm across of greenish-yellow disk florets (125-535+) with four tiny lobes at the apex of the tubular corolla; there are no ray florets. The bracts behind the flowerhead have papery edges. When crushed, both the flowerheads and the foliage give off a pineapple-like fragrance. Sources differ on the biogeography of this plant. Both the USDA Plants and NatureServe Explorer websites say it is an exotic in North America; Wikipedia, the Flora of North America, World Flora Online, and the Illinois Wildflowers website say it's native to North America. Like wild chamomile, the flowerheads of pineapple-weed can be used to make a tea.

Matricaria

Matricaria discoidea

pineapple-weed [Apr-Jul]

Field mint flowers occur in whorls of about 20 above the axils of the upper leaves. Individual flowers are 1/8" long with a green calyx with small triangular lobes; a tubular, lavender, pink, or white corolla with a two-lobed upper lip and a lower lip with 0-3 lobes; four stamens protruding well beyond the tips of the flower; and a style longer than the stamens. The fruit consists of four small nutlets nestled in the flower calyx, each with a single seed. Field mint is a very widely-distributed (circumboreal) plant. Field mint is similar to Virginia bugleweed (Lycopus virginicus) in that both have flowers in whorls in the axils of paired, opposite leaves, but the latter has only white flowers in much sparser whirls with two stamens no longer than the tips of the flower. Field mint could possibly be confused with motherwort (Leonurus cardiaca) but the latter has distinctive three or five lobed angular-cleft leaves and lacks the boldly-protruding stamens of field mint. Finally, some sources (and plant ID apps) identify "Mentha canadensis" as occurring in Illinois and neighboring states. However, both ITIS (https://www.itis.gov/) and the USDA plants database (https://plants.usda.gov/) agree that the name "Mentha canadensis," often applied to this species, is invalid and a junior synonym of Mentha arvensis (field mint).

Mentha

Mentha arvensis

field mint [Blooms: Jun-Sep]

White mulberry is species that was introduced (from Asia) in the 1600's in an attempt to established a silkworm industry in North America; it has since escaped cultivation. Individual trees are usually either male (with staminate florets in drooping, whitish to yellow-green catkins 1-1.5" long) or female (with pistillate florets in less obvious green, erect, cylindrical catkins 1.3-3/4" long), but trees that produce both male and female florets are known. Male florets are 1/4" long with a tiny green or yellowish four-lobed calyx, four stamens, and no pistil or petals. (BTW, the pollen is released by mechanically flinging it into the air via the catapult-like stamens. See Taylor et al. 2006. Sex. Plant. Reprod. 19: 19–24.) Female florets are 1/4" long with a tiny green four-lobed calyx, a single, flattened-oval ovary with two diverging white or reddish styles and no stamens or petals. The fruit is a blackberry-like compound drupe that typically changes color from green to white, but some trees have fruit that continues maturation to red and finally to black. (Those producing black fruit are often referred to var. tartarica, but that name is invalid.) White mulberry can be usually be distinguished from black mulberry by the leaves; the underside of white mulberry leaves is invariably hairless and the top surface smooth, but the underside of red mulberry leaves is covered with small hairs and the upper surface is rough. However, white and red mulberry can hybridize, which can confuse matters significantly.

Morus

Morus alba

white mulberry [Blooms: Apr-May]

Red mulberry is a native (not introduced) species that is easily confused with white mulberry (Morus alba). Red mulberry forms substantial trees 30-60' tall; it is less common in Jackson Park that white mulberry. The trunk is short with greyish-brown bark; the bark is divided into strips by shallow vertical furrows. The leaves are alternate, 4-7+" long and 3-5" across, oval or egg-shaped in outline with serrated margins and a sharp tip. The leaves can either be a simple oval with a pointed tip or a two to three (rarely five) lobed leaf with a pointed terminal lobe; the unlobed leaves are more common. Individual trees are usually either male (with staminate florets in drooping, whitish to yellow-green catkins 3/4-2" long) or female (with pistillate florets in less obvious green, erect, cylindrical catkins 3/4" long), but trees that produce both male and female florets are known. Male florets are 1/4" long with four light green sepals, four stamens, and no pistil or petals. (BTW, the pollen is released by mechanically flinging it into the air via the catapult-like stamens.) Female florets are 1/4" long with four light-green sepals, a single, flattened-oval ovary with two white to reddish, sessile stigmas and no stamens or petals. The fruit is a blackberry-like compound drupe that typically changes color from green to red to finally purplish-black with maturation. White mulberry can be usually be distinguished from black mulberry by the leaves; the underside of white mulberry leaves is invariably hairless and the top surface smooth, but the underside of red mulberry leaves is covered with small hairs and the upper surface is rough. However, white and red mulberry hybridize, which can confuse matters significantly. Leaves may be lobed, but less commonly than in white mulberry. White mulberry can be usually be distinguished from black mulberry by the leaves; the underside of white mulberry leaves is invariably hairless and the top surface smooth, but the underside of red mulberry leaves is covered with small hairs and the upper surface is rough. However, white and red mulberry can hybridize, which can confuse matters significantly.

Morus

Morus rubra

red mulberry [Blooms: ??]

Evening primrose — clusters of yellow flowers occur at the apex of the plant. The flowers are 1-2" across, with four 1/2-1" long green sepals strongly reflected over a long (3/4-2"), green, cylindrical floral tube (the ovary is located just above the leaf axil), four heart-shaped yellow petals, eight stamens, and a single style with an X-shaped stigma. The sepals typically remain connected (in pairs) along one edge until the flower opens. The seedpods develop within the ovary (the base of the elongate floral tube); they are hairy, urn-shaped with rounded edges, and have four or eight small lobes on the apex. The seeds are claimed to remain viable in the soil for up to 70 years. The flowers open at dusk and close early in the day. — — — There are (at least) three evening primroses in Jackson Park — common evening primrose (Oenothera biennis), northern evening primrose (Oenothera parviflora), and hairy evening primrose (Oenothera villosa). They are easily confused with each other. (Judging by the conflicts between the accounts on Illinois Wildflowers [https://www.illinoiswildflowers.info/], Minnesota Wildflowers [https://www.minnesotawildflowers.info/], and Missouri Plants [http://www.missouriplants.com/], even the experts are confused.) All three species have yellow flowers with an X-shaped stigma, reflected sepals, petals with a small notch in their apex, stems that may be red or green, and lance-shaped leaves with short, widely-spaced teeth. Northern evening primrose is distinguished by (1) the presence of a knob or ridge at the tip of each sepal which the other two species lack (2) a seed capsule with four robust, flaring lobes with rounded tips at the apex of the seed capsule, and (3) a stigma that is very robust and almost fills the opening of the flower. Northern evening primrose has green to yellowish-green sepals. Hairy evening primrose (often but not always) has (1) striped or reddish-tinged sepals (check the buds where this character is often easier to see), (2) flowers that turn orange as they begin to senesce (although the reliability of this character is uncertain), and (3) always has glandular hairs covering the ovary that have "pimple-like" bright-red bases; these red pimples may also occur on the stems. All three species are somewhat similar to prairie sundrop (O. pilosella); the latter has very hairy stems and leaves, and translucent lines that radiate from the base of the petals in the flowers.

Oenothera

Oenothera biennis

evening primrose [Blooms: Jul-Oct]

Smallflowered gaura is a spindly, usually unbranched plant that gets 2-6' fall, much of that the flower spike. The stem is round in section, light- to reddish-green, and covered with fine hairs. The leaves are alternate, 2-5" long and 1/4-1" across, lance-shaped, and sessile. The apex of the stem gives rise to a narrow spike of small flowers 1/2-2.5' long. Flowers open from the base of the spike towards the tip with relatively few open at any one time. Individual flowers are about 1/4" across. They consist of four sepals reflected back along the elongated, cylindrical, light-green or red flower stalk/ovary, four spreading white or pink petals, eight stamens, and a long style with a X-shaped (or four-lobed) stigma. The flowers are said to open in the evening and close in the morning. The seed capsules develop from the ovary; they are about 9 mm long. The flowers and flower spike of smallflowered gaura are quite distinctive and unlikely to be confused with any other species.

Oenothera

Oenothera curtiflora

smallflowered gaura [Blooms: Jul-Sep]