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Lady's-thumb is an exotic, native to Europe, but has a long history in North America — it was first reported from the Great Lakes in 1843. Flower spikes (racemes) are 1/2-1.5" long and densely covered with tiny (1/8" long) pinkish-white flowers; flower color is quite variable, even within a single flower spike. The flowers are "shy" and often open only at the tips of the 4 or 5 sepals (there are no petals); both the six stamens and the single style (divided into three towards the distal end) remain hidden. Seeds are black; they develop singly within the persistent sepals and remain largely hidden by the sepals; they can be found on flower heads still blooming. Lady's-thumb prefers wet habitats.

Persicaria

Persicaria maculosa

lady's-thumb [Blooms: Jun-Sep]

Pennsylvania smartweed flower spikes are 3/4-2" long, distinctly cylindrical with a blunt tip, erect, and densely covered with white, pink, or reddish flowers, only a few of which are open at any time. The peduncle of the flower spike is usually covered with short glandular hairs. Individual flowers are ~1/8" long, and have five tepals (white, light pink, or rose pink), 6-8 stamens with yellow, white, or pink anthers and two styles. Pennsylvania smartweed is a particularly variable species and may be difficult to identify unequivocally. If the stems zig-zag between nodes, if the flower stalks' peduncules are covered with glandular hairs, or if the flower spikes are short, cylindrical and erect, the specimen is likely to be Pennsylvania smartweed, but any or all of these features may be missing.

Persicaria

Persicaria pensylvanica

Pennsylvania smartweed [Blooms: Jul-Sep]

Dotted smartweed (Persicaria punctata) is a very common smartweed in Illinois wetlands. The upper stems produce spike-like racemes 2-6" long with white to greenish-white flower buds and flowers sparsely distributed along their length. Individual flowers are about 1/8" long with five white tepals covered with glandular depressions (best viewed with a hand lens). There are 6-8 stamens with red or pink stamens; the single style divides into two or three branches near its base. The flowers only open at their tips. The single seed is three-angled, oblong, and shiny brown to black; it remains tightly enclosed in the tepals as it develops. In Jackson Park, only dotted smartweed and waterpepper (Persicaria hydropiper) have glandular depressions on the surface of the flower tepals.

Persicaria

Persicaria punctata

dotted smartweed [Blooms: Aug-Sep]

Cleft phlox flowers are supported by 1" pedicels, are 3/4" across, white or pale violet, with a tubular corolla that flares into five petal-like lobes that are each deeply cleft at their tips; the throat is very narrow. A three-lobed stigma and the orange anthers of the stamens lie just within the opening to the throat of the flower. Cleft phlox is endemic to the Midwest. The cleft petal lobes distinguish cleft phlox from all other Phlox species.

Phlox

Phlox bifida

cleft phlox [Blooms: Apr-?]

Woodland phlox is a 1-1.5' tall plant with a fuzzy to hairy stem, light green or reddish brown in color. Leaves are opposite (or sometimes in a three-leaf whorl), sessile or clasping the stem, three times longer than wide, lance-shaped with smooth margins, and fuzzy to hairy overall with short hairs around the margins. The flowers are 1" across, pale blue-violet, lavender, or (rarely) white, and with a long, narrow tubular throat that abruptly flares into five petal-like, spoon-shaped lobes. The calyx is green or reddish-green, hairy, with five long, narrow teeth almost half the length of the flower, spreading near their tips. The five stamens and style are hidden within the throat. Woodland phlox has relatively broader leaves than other Phlox species and has a more intense blue-violet (and less pink) color.

Phlox

Phlox divaricata

woodland phlox [Blooms: Apr-May]

Smooth phlox is a 1-2' tall plant with an unbranched, hairless stem topped with a slightly domed cluster of 3-20 pink or lavender flowers. Each flower is about 3/4" across and has a long, tubular throat that abruptly flares into five petal-like lobes; each lobe is wedge-shaped and overlaps the next lobe clockwise. The calyx (also hairless) consists of five triangular segments that taper rapidly to sharp points; the calyx is <1/3 the length of the corolla tube. The five stamens and single style with a three-part stigma either lie within the corolla tube or are just visible in the throat. After fertilization, a narrow seed capsule filled with numerous seeds fills the persistant calyx. Smooth phlox prefers moist to wet habitats. Smooth phlox flowers resemble prairie phlox (P. bifida) but the latter species is quite hairy on the stems, leaves, and the exterior of the flower (the calyx); smooth phlox is hairless. Checking the hairiness (or lack thereof) of the calyx is the quickest way to tell prairie phlox from smooth phlox.

Phlox

Phlox glaberrima interior

smooth phlox [Blooms: Jun-Aug]

Prairie phlox is a compact, single-stemmed, plant 1/2-1.75' tall with (typically) a dome-shaped cluster of flowers at the apex. Individual flowers are 1/2-3/4" across, pink or lavender (rarely white); the corolla is tubular with five wedge-shaped, petal-like lobes often with darker markings (nectar guides) near the throat; the corolla is hairy on all external surfaces. The throat is very narrow; the five stamens with yellow anthers are recessed but just visible. The very short, tubular, hairy calyx base is green, with five long, narrow teeth that extend parallel to the narrow throat (also hairy) of the corolla. The fruit is oval and shorter than the calyx (in which it develops); when ripe, the capsule splits explosively, flinging the seeds in all directions. The species name ("pilosa") means "hairy" in Latin, and this species is indeed hairy on almost every surface. Prairie phlox flowers resemble smooth phlox (P. glaberrima) and, to a lesser extent, woodland phlox (P. divaricata), but the former species is quite hairy on the stems, leaves, and the exterior of the flower (the calyx); smooth phlox is hairless. Checking the hairiness (or lack thereof) of the calyx is the quickest way to tell prairie phlox from smooth phlox; checking the hairiness of the exterior of the corolla tube will distinguish woodland phlox (hairless) from prairie phlox (hairy).

Phlox

Phlox pilosa

prairie phlox [Blooms: Apr-Jun]

Clammy groundcherry flowers arise at the junction of two branches or at a leaf axil on 1/4", arching pedicels that permit the flower to droop. The flowers are up to 3/4" across, consisting of a green calyx half the length of the flower with five triangular teeth, a funnel-shaped, pale-yellow corolla with five shallow lobes, five stamens with large, creamy-yellow anthers, and a single central pistil. In the interior of the corolla surrounding the ovary are five brown smudges, one on each corolla lobe, that merge centrally into a purple-brown ring covering the ovary. Both the pedicel and the calyx are also covered with fine white hairs. After fertilization, the flowers are replaced by green (later brown) hollow husks (a persistant calyx), heart-shaped in longitudinal section, covering a 1/2" diameter spherical, green fruit that becomes yellow when ripe. All parts of clammy ground cherry contain a glycoalkaloid poison called solanine that causes a series of unpleasant and sometimes potentially fatal symptoms; clammy groundcherry is avoided by mammalian herbivores. Only the RIPE fruit is edible.

Physalis

Physalis heterophylla

clammy groundcherry [Blooms: Jul-Aug]

Smooth groundcherry flowers are yellow, bell-shaped, with five purplish-brown patches near the center, five stamens with yellow or purple anthers, and a single pistil; the flowers are suspended from a purplish-green pedicel 3/4-1" long. After fertilization, the flowers are replaced by a tomatillo-like fruit (often with ten purple meridional lines) that is a green (later brown) hollow husk (a persistant calyx) that is heart-shaped in longitudinal section, covering a 1/2" diameter spherical, green miniature tomato that becomes yellow when ripe. All parts of smooth groundcherry contain a glycoalkaloid poison called solanine that causes a series of unpleasant and sometimes potentially fatal symptoms; smooth groundcherry is avoided by mammalian herbivores. Only the RIPE fruit is edible (said to taste like an underripe strawberry).

Physalis

Physalis longifolia

smooth groundcherry [Blooms: Jun-Aug]

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]

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]

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]

Silverweed is a low, sprawling native plant that occurs everywhere in North America from the southwest through northern Canada. The prominent red stolons give rise to both new rooted nodes where the stolons encounter wet soil and may also give rise to new leaves. There is a basal rosette of large (12" long x 4" wide) odd-pinnate leaves with 5-11 opposite leaflet pairs and a single terminal leaflet. Flower pedicels 2-6" long arise from stolon nodes. The flowers are bright yellow, solitary, and 3/4" across. Each flower has five light green, hairy sepals; 5-15 oval, yellow petals; a ring of ~20 yellow stamens with large flat anthers; and a central disc of 20 to over 100 yellow pistils. The sepals are shorter than the petals. Silverweed prefers sandy habitats like beaches.

Potentilla

Potentilla anserina

silverweed [Blooms: Jun-Aug]

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]