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Ninebark produces round or domed clusters (racemes) of 30-50 flowers on the tips of young stems. Individual flowers are about 1/2" across; they have a light green calyx with five triangular teeth, five white petals, 30-40 pink-tipped stamens, and 3-5 styles with yellow stigmas. The inside surface of the flower between the styles and the base of the stamens (the hypanthium) is prominently colored tan, orange, or red. After fertilization, each flower produces 2-5 adjacent fruits "follicles"), greenish-red in color, drooping from the long, slender flower pedicels. Single follicles contain a single, hard seed; the follicles are about 8 mm long with a slender, pointed beak protruding from one side. There are two varieties of ninebark characterized by whether the surface of the follicle is hairy; the variety present in Jackson Park (var. intermedius) has a hairy surface.

Physocarpus

Physocarpus opulifolius

ninebark [Blooms: May-Jun]

Pokeweed inflorescences are cylindrical, 3-6" long and 1" in diameter with 1/4" flowers radiating in all directions on short green or white pedicels. Individual flowers have five pink or white sepals and ten white stamens in a circle around fused carpels that form a lobed dome with ten tiny, thread-like styles in the center; petals are absent. The fruit is a 1/4" wide M&M-shaped berry that becomes dark purple and shiny when ripe; the pedicels also turn reddish-purple. Pokeweed is impossible to confuse with any other local plant. Children appear to be especially sensitive and may need hospitalization after eating only a few ripe berries.

Phytolacca

Phytolacca americana

pokeweed [Blooms: Jun-Oct]

The stems and flower stalks of Jacob's ladder are green to reddish-green and hairy; the flowers occur in panicles of floppy flowers on 1" long pedicels. The flowers are bell-shaped and baby-blue in color, 3/8" across with fine longitudinal veins. There are five stamens with white anthers and a long style tipped with a Y-shaped stigma. The stamens do not project beyond the flower margins, but the style does. The fruit is an ovoid, three-celled, seed capsule about 1/4" long held in the remnants of the calyx. Jacob's ladder prefers shady woodlands. This species is similar to Greek valerian (Polemonium vanbruntiae) but the latter species has stamens that extend beyond the flower margins (and does not occur in Illinois).

Polemonium

Polemonium reptans

Jacob's ladder [Blooms: Apr-May]

Solomon's seal is a 2-3.5' tall plant with a single, unbranched, hairless, arching stem. On the underside of the stem are 12-20 dangling clusters of flowers (2-3 flowers/cluster). The flowers are 1/2-1" long, whitish- or yellowish-green, tubular, with six lobes/tepals fused for most of their length but that flare slightly at their tips; the interior of the flower contains six stamens with yellow anthers and a single style. The fruit is a 1/4" diameter spherical berry, initially green, dark blue-violet or -black when mature. When in bloom or bearing fruit, Solomon's seal is distinctive and easy to identify; when not in bloom, the leaves of Solomon's seal can be difficult to distinguish from those of false Solomon's seal (Maianthemum racemosum) and starry false Solomon's seal (Maianthemum stellatum). (Both Maianthemum sp. have short petioles on their leaves and their flowers are terminal, at the end of the stem, rather than hanging down from the stem.) Polygonatum biflorum is sometimes (incorrectly) referred to as Polygonatum commutatum. The "Solomon's seal" in the name refers to scars on the rhizome fancied to look like a Hebrew seal. I have to admit I just don't see it.

Polygonatum

Polygonatum biflorum

Soloman's seal [Blooms: May-Jul]

Prostrate knotweed is a summer-blooming Eurasian exotic that is widespread and ubiquitous across Illinois. One to five 2-3 mm long flowers occur in a cluster at the base of the leaves; the flowers have very short petioles but may appear sessile. Individual flowers have five white or green and white sepals, no petals, five or eight stamens with yellow anthers, and three styles (one for each carpel) fused into a single pistil with a tripartite yellow stigma fringed with short hairs. The fruit develops within the persistant sepals of the flower. Prostrate knotweed is not fussy about its habitat and withstands a fair amount of foot traffic.

Polygonum

Polygonum aviculare

prostrate knotweed [Blooms: Jun-Sep]

Eastern cottonwood is dioecious; flowers are either male or female and occur on separate trees. The flowers, whether staminate or pistillate, are produced on catkins 2-3" long; the flowers are wind pollinated. Male catkins are produced in clusters of 2-4 near branch tips; they are bright red or yellow, cylindrical, and densely covered with male florets. The male florets have a fringed bract at their base, above which is a basal disc with 30-40 reddish or yellowish stamens. Female catkins are solitary (not in groups), cylindrical, and green, covered with numerous female florets on slender petioles. Each female floret rests on a fringed bract above which is a dish-shaped three- or four-carpelled basal disc with a single, oval pistil about 8 mm long with 2-4 apical, yellowish, flattened stigmas with undulate margins. After fertilization, the female catkins elongate to a length of 4-6" while individual ovaries enlarge; at maturity, each fruit splits to release 30-50, 2 mm long, seeds suspended on cottony hairs. The seeds are both wind and water dispersed.

Populus

Populus deltoides

Eastern cottonwood [Blooms: Apr-May]

Common purslane has no inflorescence per se; flowers occur alone or in small terminal clusters. Individual flowers are 1/8-1/4" across with two or four green sepals, 4-6 yellow petals with notched tips, 6-12 stamens with yellow anthers, and a five-lobed style with 3-6 stigmas. Fertilized flowers are replaced by an oval or urn-shaped capsule about 8 mm long that splits open along a meridional seam to release the tiny, dark brown or black seeds.

Portulaca

Portulaca oleracea

common purslane [Blooms: Jun-Sep]

In late spring and early summer, curly pondweed produces both flowers and turions (a detachable, dormant bud, a.k.a. a "winter bud"). Cylindrical flower spikes 1-1.5" long arise from the tips of the stems or the axils of upper leaves; peduncles up to 3" long hold the flower spikes just above the water. Each flower spike may have 3-5 whorls of flowers. Individual flowers are tiny (3 mm across); they consist of four greenish-brown or greenish-red sepals, four stamens with a ladle-shaped appendage, and four ovules topped by a four-part style. Flowers may be pollinated by either wind or water. Fertilized ovules produce a dry seed (a maximum of four per flower) that is generally oval but asymmetrical in detail with a knobby keel along one edge and a long, curved beak or tooth at the opposite end. Seed germination has never been observed. Simultaneously, the plant produces turions — rosettes of small, holly-like leaves that overall have a cone-like appearance — from the tips of stems and leaf axils. After the fruits and the turions are released, the rest of the plant degenerates over the course of the summer. The turions sink to the bottom of the water body and root, forming small plants that overwinter.

Potamogeton

Potamogeton crispus

curly pondweed [Blooms: May-?]

Rough cinquefoil is considered to be native to both North America and Eurasia. Flowers may develop from the axils of the upper leaves but more usually occur (as a panicle of cymes) in a terminal inflorescence on flower stalks 1-2' tall. The flowers are small (1/3-1/2") and pale yellow; the petals are distinctly heart-shaped with narrow bases and the sepals are triangular and slightly longer than petals. About 15-20 yellow stamens surround a dome-shaped, yellow receptacle covered with styles. Beneath the sepals are five green oval bracts about the same length as the sepals when the flower is in bloom. Fruits develop as dry seeds (achenes) in the persistent flower calyx. Note that rough cinquefoil’s leaves have three leaflets, common cinquefoil's leaves have five, and prairie cinquefoil's leaves have 7-11.

Potentilla

Potentilla norvegica

rough cinquefoil [Blooms: Jun-Sep]

Sulfur cinquefoil flowers are 3/4" across, pale yellow with a golden center. Beneath the flowers are green bracts about the same length as the sepals but narrower. The sepals are equilateral triangles that are shorter than the petals while the petals are heart-shaped with the narrow point at the base of the petal (where the yellow color is often more intense). There are 25-30 stamens surrounding the central receptacle; the anthers have one or more central dark spots contrasting strongly with the generally yellow anther (but these spots may be difficult to see). Sulfur cinquefoil is similar to prairie cinquefoil, but sulfur cinquefoil's flowers are yellow, not cream colored and its leaves are palmately compound, not pinnate. After fertilization, the sepals close over the ovary forming a capsule around the maturing seeds. The seeds are dry achenes less than 2 mm long with a coarsely wrinkled, brown surface. Sulfur cinquefoil was accidentally introduced to North America from Europe; the first recorded observation was in Montreal in 1852. By 1879, sulfur cinquefoil had become naturalized in New York state; by 1900, it was spreading across New England and the upper midwest. (So sulfur cinquefoil probably wasn't around for the Columbian Exposition in Jackson Park in 1893.) It spreads aggressively in disturbed areas.

Potentilla

Potentilla recta

sulfur cinquefoil [Blooms: May-Jul]

Common cinquefoil is a sprawling plant less than a foot tall that produces numerous prostrate stolons up to 3' long. Both the stems and the stolons are initially green but become more reddish. The leaves are alternate and palmately compound with five leaflets, each with serrated margins; the leaflets are three to four times longer than wide. The sparse flowers develop singly on long pedicels that arise from the axil of some compound leaves. They are bright yellow and 1/2" across with triangular sepals shorter than petals; the petals are narrowest at their base and usually rounded at their distal edge. About 20 stamens with yellow anthers (turning reddish with age) surrounded a central mass of styles. Common cinquefoil has flowers and leaves that are superficially similar to those of mock strawberry (Duchesnea indica). However, the leaves of common cinquefoil have extremely sharp-edged, well-defined teeth on the leaf margins (strongly resembling the edge of a hand saw), not the bluntly-tipped teeth of mock strawberry. The five small bracts (leaves) just below the sepals in mock strawberry, each with three pointed lobes at its tip, are present in both the flowers and berries are diagnostic of mock strawberry; they are absent in common cinquefoil. Note that rough cinquefoil’s leaves have three leaflets, common cinquefoil's leaves have five, and prairie cinquefoil's leaves have 7-11 leaflets.

Potentilla

Potentilla simplex

common cinquefoil [Blooms: May-Jul]

American plum flowers first appear before or at leaf emergence; they occur in roughly spherical clusters (umbels) of two to five flowers, arising from leaf axils. Each flower is ~1" across, held away from the twig at the base of the umbel on 1/2-1" petioles; there are five egg-shaped petals with narrow bases, white with a touch of pink, five narrow, somewhat fleshy, green sepals much shorter than the petals, a single style, and numerous (10-30) stamens with tan anthers. The fruits are about 1" across, initially green but turning reddish-purple with the waxy bloom typical of plums when ripe; inside is a single seed (a "stone," like a peach). Because this tree usually flowers when the leaves are only beginning to open, it produces an especially showy display. It is widespread across Jackson Park.

Prunus

Prunus americana

American plum [Blooms: Apr-May]

The floral inflorescence in sweet cherry is a flat-topped corymb of two to six cup-shaped flowers that appears in early spring as the new leaves unfold. Each flower is 1-1.5" in diameter with five green sepals reflexed back along the petiole; five pure white petals; a ring of 20-30 stamens each with a white filament tipped with a yellow, ball-like stamen; and a single pistil with a terminal knob-like, greenish stigma. The fruit is a red to dark purple drupe (stone fruit) 1/2-1" in diameter (a typical cherry).

Prunus

Prunus avium

sweet cherry [Blooms: Apr]

European bird cherry It has showy white flowers (so is widely planted as an ornamental) and reaches heights of 30-40'. Blooms are produced in elongate, cylindrical racemes of 15-50 flowers at the tips of twigs, similar to but shorter than those of chokecherry (Prunus virginia). Individual flowers consist of five green, broadly-spreading or reflexed sepals (longer than wide); five white or cream colored petals that are 1/4-3/8" long, oval but widest in the center; 10-30 stamens half the length of the petals around a cup-shaped, often green hypanthium (hairless externally); and a single central pistil. The fruit is a small, black drupe (cherry) with an extremely bitter taste to mammals, but it is much loved by birds, who disperse the pits. European bird cherry is very similar to another species present in Jackson Park, chokecherry. European bird cherry tends to be more tree-like in habit than chokecherry and tends to have shorter stamens (half the length of the petals) than chokecherry (as long as the petals). It's not clear how much of this expansion is due to Park District policy and how much is due to natural seed dispersal.

Prunus

Prunus padus

European bird cherry [Blooms: Apr-May]

Peach flowers arise along young branches, blooming beginning before the leaves have opened in the spring; the flowers are usually solitary but occasionally occur in pairs. Individual flowers are 1-1.5" long consisting of a burgundy-colored calyx with five rounded apical lobes (sepals); five spreading pink (rarely, white) petals, oval with abruptly narrowed bases ("clawed"); 15-30 stamens with pink filaments and yellow to orange anthers; and a pistil with a single light green style nearly as long as the stamens. Fertilized flowers are replaced by green, fuzzy ovoids, eventually up to 3" long and across and containing a single seed; peach-colored when mature.

Prunus

Prunus persica

peach [Blooms: Apr-May]

Sand cherry is a 4-8' tall shrub; the Great Lakes variant of this species (Prunus pumila spp. pumila) is restricted to the states (and the Canadian province) that touch on the Great Lakes. Blooms occur in umbels of 1-3 flowers; flowers open before the leaves but may persist after some leaves have emerged. Individual flowers are about 1/2" across, consisting of five sepals with rounded tips that are about a third the length of the petals; five white, round- or egg-shaped petals; 10-30 white stamens with yellow anthers emerging from a reddish, cup-shaped hypanthium; and a single, central style. The fruit is a reddish-purple to black, shiny cherry (drupe) about 1/2" in diameter. Sand cherry is found along the shores of the Great Lakes on beaches (sandy, gravelly, or rocky), dunes, and the swales between dunes.

Prunus

Prunus pumila

sand cherry [Blooms: Apr-May]

Black cherry (Prunus serotina) is a is a deciduous tree that can grow up to 80' tall. It typically has a single central trunk below and leafy crown that is taller than wide. Flowers occur in racemes 4-6" long with 20-60 1/2" wide flowers packed around the elongated inflorescence. Individual flowers consist of five green, triangular sepals, five white petals broader at their distal tips and at least three times longer than the sepals, 10-30 stamens with yellow anthers around a reddish-orange hypanthium, and a single, central pistil with a flattened stigma. After fertilization, each flower produces a globoid, fleshy drupe about 1/4" across. The immature cherries are green; as they mature the fruit turns first dark red, they purple-black at maturity. These fruits are sweet but slightly bitter; the black cherry you buy in the grocery store is larger (at least 1/2" across), sweeter, and a species native to Eurasia (Prunus avium).

Prunus

Prunus serotina

black cherry [Blooms: May-June]

Japanese flowering cherry is an exotic from East Asia widely grown in North America as an ornamental (for its showy spring flowers). The flowers occur is small clusters of 2-5 white, pale pink, or deeper pink flowers that (unlike most cherries) dangle face-down beneath the stems from short spurs. The fruit consists of small, round drupes that turn black when mature. Leaves, stems, and fruit, and seeds are toxic to mammals. Many of the cultivars of Japanese flowering cherry are highly hybridized and nearly unrecognizable as being derived from Prunus serrulata.

Prunus

Prunus serrulata

Japanese cherry [Blooms: Apr-May]