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The yellow-flowered wood-sorrels in general (of which yellow wood sorrel is one) are difficult to distinguish and have given rise to much taxonomic confusion. (I.e., it's not just us; even the pros have problems. Read on.) Flowers are 3/8-1/2" across; they have five light green sepals, shorter than the petals, five yellow petals with rounded tips, ten stamens with yellow anthers, and a single pistil with five styles fused except at their tips. These flowers often have a ring of red lines around the throat (like yet another species, O. illinoensis). The seed capsules are 1/4-1/2" long, banana-shaped, erect, hairy, and five-sided; the capsules use explosive seed dispersal (like jewelweed and wild geranium) to scatter the contained seeds. This species is very similar to another yellow wood sorrel, Oxalis dillenii; see https://www.minnesotawildflowers.info/flower/yellow-wood-sorrel for details on how to distinguish the two. (A good hand lens or a microscope are required.)

Oxalis

Oxalis stricta

yellow wood-sorrel [Blooms: May-Sep]

Cowbane is a spindly, sparse plant 2-5' tall. At their apex, the stems produce shallowly dome-shaped compound umbels 3-5" across of 10-25 umbelletes of 10-20 small white flowers each. Individual flowers are about 3 mm across; each has a short calyx, five white petals with notched tips, five stamens with white anthers, and a central greenish or white ovary with two styles. The fruit is a elongate (1/4" long), flattened oval with wings on the flattened edges, longitudinal stripes/ribs and, initially, with the remnants of the two styles at their tips; when mature it splits, releasing two seeds. Cowbane prefers wet soils. As you might suspect from the name, it is toxic if eaten.

Oxypolis

Oxypolis rigidior

cowbane [Blooms: May-June]

Butterweed stems produce a flattened panicle of flowers about 6" across with a single series of bracts (phyllaries) surrounding the base of the flowerhead. Individual flowerheads are 1/2" across with 5-15 yellow, narrowly-oblong pistillate ray florets and 35-50+ yellow, tubular disk florets with five apical lobes a single style that extends just past the anthers, and five stamens attached to the inside of the tubular corolla; the disk is 4-5 mm across. The fruit is a single, five-angled seed with a tuft of white hairs (like a dandelion). Butterweed contains toxic compounds (probably pyrrolizidine alkaloids) which deter most mammalian herbivores (although some domestic herbivores do eat it and suffer the consequences). According to ILW, butterweed was typically restricted to southern Illinois, with a few recent occurrences in central Illinois. Apparently, it has now made its way to Cook County. Butterweed (Packera glabella), balsam ragwort (Packera paupercula), and prairie ragwort (Packera plattensis) are easy to confuse — all bloom in the late spring/early summer and all are weedy-looking plants with yellow/golden-yellow, daisy-like flowers. With one exception, the flowers don't help to distinguish them; however, the petals of butterweed, seen from behind, have a strap-shaped blade with 2-3 teeth at the distal end and a narrow tube (the corolla tube) about a quarter the length of the strap connecting the strap to the rest of the flower (not present in the ragworts). In general, you'll need to look carefully at the leaf shape and presence/absence and quantity of wooly fine white hairs on the leaves and stems. Butterweed has large (10" long) basal leaves; the leaves are pinnatifid with multiple semicircular lobes and a circular terminal lobe. Balsam ragwort (Packera paupercula) basal leaves are no longer than 3", the flowerheads have 0, 8, or 13 ray florets, the phyllaries behind the flowerhead are purple-tipped, and wooly hairs are usually found in the leaf axils. Prairie ragwort (Packera plattensis) is extensively covered with white wooly hairs on the stems, leaves, leaf axils, and on the phyllaries behind the flowerheads.

Packera

Packera glabella

butterweed [Blooms: May-Jun]

Mature wild quinine plants are 2-3' tall. On the flowering stalks (and the side branches) are flat topped clusters of white, button-like flowerheads about 3/8" across. (The Illinois Wildflowers website considers them "similar to a head of cauliflower.") Flowerheads are composed of 15-35 disk florets, often with blackish, club-like stamens poking out; the 5-6 ray florets bear a tiny, cup-shaped petal and a pistil with a bifurcated stigma. No other wildflower in Illinois has flowerheads anything like wild quinine; common and widespread in Jackson Park.

Parthenium

Parthenium integrifolium

wild quinine [Blooms: May-Aug]

Virginia creeper produces panicles of 80-150 flowers opposite leaf nodes; the panicles are broader than long and have a distinct central axis. Individual flowers are 1/4" across, green, with five petals, five white stamens with yellow anthers, and a single stout, cone-shaped style. Flowers may have only stamens, only pistils, or both pistils and stamens. The petals have a raised margin (less so than woodbine) and are reflected backwards around the flower stalk. The fruit is a fleshy berry that is initially green but becomes blue-black with maturation; the flower stalks become orange-red or red as the fruit matures. The clusters of the fruit are reminiscent of a bunch of grapes. Opposite the leaf nodes are tendrils with as many as 10 branches; the tendrils end in distinct (adhesive) pads. Virginia creeper plants growing on trees produce aerial roots with a distinct "beard" of rootlets. Woodbine (Parthenocissus vitacea) also has palmate leaves with five leaflets, very similar to Virginia creeper (P. quinquefolia), but lacks the distinctive "bearded" aerial roots with short rootlets that are present in Virginia creeper. Opposite the base of the leaf petiole on the stem, woodbine produces a thin filament that branches 2-3 times, anchoring the vine by twining around objects. In Virginia creeper, the equivalent filaments are stouter, branch up to ten times, and end in robust, egg-shaped pads that attach to the substrate. The inflorescence of woodbine lacks a central axis; the inflorescence of Virginia creeper has a distinct central axis. Wikipedia (https://en.wikipedia.org/wiki/Parthenocissus_inserta) lists other differences between the two species. Illinois Wildflowers, USDA Plants, and and World Flora Online consider the two species to be one; Minnesota Wildflowers considers them to be separate and distinct. Flora of North America indicates the correct scientific name for woodbine is Parthenocissus vitacea (not P. inserta), as does ITIS and MissouriPlants.com, implying that woodbine and Virginia creeper are distinct species. Both woodbine and Virginia creeper have 40 chromosomes. Lu et al.'s (2012, 2023) molecular and morphological analyses indicate that woodbine and Virginia creeper are very closely related but distinct species and I'll consider that to be correct here.

Parthenocissus

Parthenocissus quinquefolia

Virginia creeper [Blooms: June]

Boston ivy is an exotic introduced from Asia; it is a woody vine up to 50' long (with occasional branches) that grows on or over fences, walls, concrete, masonry, and trees. The lower stems are woody and produce small brown rootlets to adhere to surfaces; upper stems are (also) hairless, green to orange-red in color, with branched tendrils that have adhesive pads at their tips. Leaves are alternate, 6" long and across exclusive of the long, slender petioles, palmately tri-lobed with undulating or crenate margins. Cymes of flowers lacking a distinct central axis arise from the leaf axils; the cymes are 4" in both dimensions. Individual flowers are 1/4" across; they have five yellowish-green petals, five stamens with yellow anthers, and a single style. Fertilized flowers produce berries 3/8" across. When mature the berries are dark blue with a whitish bloom, usually hidden beneath the leaves; the flower stalks are yellow- or brownish-green or a dull orange-red.

Parthenocissus

Parthenocissus tricuspidata

Boston ivy [Blooms: ??]

Woodbine is a woody vine that usually uses trees as a substrate; the vine can be as much as 60' long. The stem is initially green and hairless; as it matures it becomes woody and develops a reddish- or grey-brown color. The leaves are alternate, palmately compound, usually with five (rarely 4 or 7) leaflets that are about 5" long and 2.5" wide with coarse marginal teeth, shiny-green when young but getting duller with age; the compound leaf has a slender 6-8" long petiole. Three- to six-inch-long clusters of 10-75 flowers arise from the main vines opposite the leaves; the clusters have two main branches and multiply-branched flower stalks with no clear central stem. Individual flowers are inconspicuous, 1/4" across with five yellowish green petals with narrow margins perpendicular to the plane of the petal and a pointed, curled tip; the petals are initially spreading but later become reflected backwards. In the center of the flower are five pale red stamens with creamy white or purple anthers, a reddish ovary, and a single white, stubby, conical style. The fruits are round blue-black berries 3/8" across that are reminiscent of grapes in a cluster with red, branched flower stalks; each berry contains four seeds. Woodbine has palmate leaves with five leaflets, very similar to Virginia creeper (Parthenocissus quinquefolia), but lacks the distinctive aerial roots "bearded" with short tendrils that are present in Virginia creeper. Opposite the base of the leaf petiole on the stem, woodbine produces a thin filament that branches 2-3 times, anchoring the vine by twining around objects. In Virginia creeper, the equivalent filaments are stouter, branch up to 10 times, and end in robust, egg-shaped pads that attach to the substrate. The inflorescence of woodbine lacks a central axis; the inflorescence of Virginia has a distinct central axis. Wikipedia (https://en.wikipedia.org/wiki/Parthenocissus_inserta) lists other differences between the two species. Illinois Wildflowers, USDA Plants, and and World Flora Online consider the two species to be one; Minnesota Wildflowers considers them to be separate and distinct. Flora of North America indicates the correct scientific name for woodbine is Parthenocissus vitacea (not P. inserta), as does ITIS and MissouriPlants.com, implying that woodbine and Virginia creeper are distinct species. Both woodbine and Virginia creeper have 40 chromosomes. Lu et al.'s (2012, 2023) molecular and morphological analyses indicate that woodbine and Virginia creeper are very closely related but are distinct species, and I'll consider that to be correct here.

Parthenocissus

Parthenocissus vitacea

woodbine [Blooms: ??]

Wild parsnip is an exotic plant, native to Eurasia, in the carrot family (Apiaceae); it produces flat umbels of flowers (like Queen Anne's lace, except yellow). This is the wild version of the domestic parsnip. The compound umbels are 3-8' across, flat topped, with 15-25 umbellets; each umbellet includes 15-35 1/8" yellow flowers borne on 3/8" long pedicels. Individual flowers have five very short, yellow petals, initially curled inward, but later the petals reverse curvature and curl outwards; there are also five yellow stamens and two styles that arise from an ovary with a swollen, greenish-yellow nectar pad. The fruits are 1/4" long flat, oval, coin-like discs; when mature the disk is brown and the edges of the disk are winged.

Pastinaca

Pastinaca sativa

wild parsnip [Blooms: May-Jun]

Calico penstemon (aka, long-sepaled penstemon) is a typical penstemon/beardtongue — 1-3' tall with an unbranched stem and a panicle of flowers at the apex of the stem. Flowers are about 1" long, with a calyx with five long (5-12 mm), narrow (1-2 mm) lobes, a tubular corolla with two upper lobes and three lower lobes on the aperture, and four stamens and a single style, all enclosed by the corolla. The corolla's exterior is light purple or light violet and covered in fine hairs; the interior of the corolla is white and smooth, without ridges. The lobes on the lower lip of the corolla do not protrude beyond the lobes of the upper lip. Calico penstemon is fairly rare in Jackson Park.

Penstemon

Penstemon calycosus

calico penstemon [Blooms: Jun-Jul]

Foxglove beardtongue's inflorescence consists of 3-6 pairs of panicles at the apex of the stems. Individual flowers are white or (less often) pink with a green or maroon calyx, five narrowly triangular lobes, and a tubular corolla that flares abruptly distal to the calyx. The corolla's aperture bears five lobes (two above on the upper lip, three below on the lower lip) with pink or purple nectar guides inside the tube. The filament of a sterile stamen (a "staminode") bearing sparse yellow hairs runs along the midline of the lower half of the corolla, while the filaments of the other four stamens wrap around the inside of the corolla like ribs in a ribcage, with the black anthers positioned on either side of the midline of the upper corolla. A single style runs along the upper midline between the black anthers to emerge between the two upper aperture lobes. The fruit is a bullet-shaped capsule about 1/2" long nestled in the persistant calyx. The calyx, flower stalks, and the flowers themselves are densely covered by glandular hairs; the main stems and leaves are hairless. Foxglove beardtongue is ubiquitous in Jackson Park.

Penstemon

Penstemon digitalis

foxglove beardtongue [Blooms: May-Jul]

Slender beardtongue (aka, lilac penstemon) is another beardtongue/penstemon that is uncommon in Jackson Park. The stems are unbranched, green or purple, and may or may not bear hairs. There are both basal and stem leaves. The basal and lower stem leaves are 1-3" long and 1/2" wide, variable in shape and leaf margins; the stem leaves are smaller and minutely toothed. Individual flowers are pinkish, purple, or pale violet, about 3/4" long; they are comprised of a green calyx with five triangular lobes and a tubular corolla that is abruptly inflated in the more distal two thirds of the flower. The lower lip of the corolla has three lobes that extend down and out from the aperture the upper lip has two smaller, erect lobes. The interior of the corolla is white with several dark purple lines that act as nectar guides. The filament of a sterile stamen (a "staminode") bearing sparse yellow hairs runs along the midline of the lower half of the corolla, while the filaments of the other four stamens wrap around the inside of the corolla like ribs in a ribcage, with the black anthers positioned on either side of the midline of the upper corolla. A single style runs along the upper midline between the black anthers. The fruit is a more or less bullet-shaped capsule nestled in the persistant calyx. The calyx, flowers, and flower stalks are all covered with glandular hairs; the stems and leaves are not.

Penstemon

Penstemon gracilis

slender beardtongue [Blooms: Jun-Jul]

Large-flowered penstemon flowers develop in the axils of the stem leaves in pairs. (Occasionally a triplet will arise.) Individual flowers are up to 2" long, pale lavender or pink, tubular, sightly flattened vertically but flaring at the aperture, with a two-lobed upper lip and 3-lobed lower lip with purple lines on the interior. The bluish-green calyx has five teeth. A distinct longitudinal ridge runs along the upper surface of the corolla, intersecting the aperture between the two upper lobes. A white style with a tiny stigma runs along the inside of the corolla under the longitudinal ridge and protrudes from the throat. The four fertile stamens are recessed, with their filaments wrapped around the inside of the corolla like a ribcage and the anthers on either side of the dorsal midline; the fifth (sterile) stamen runs along the lower midline and ends in a recurved or coiled tip with a prominent pad bearing short, brilliant-yellow hairs. The fruit is a teardrop-shaped seed pod nestled in the remains of the calyx. Large-flowered penstemon prefers poorer but well-drained soils with significant rocky material or sand. This species is officially listed as "endangered" in Illinois.

Penstemon

Penstemon grandiflorus

large-flowered penstemon [Blooms: May-Jul]

Hairy beardtongue is 1-2.5' tall and blatantly hairy — backlit plants seen from a distance show a white nimbus around the stems. The flowers are slender, lavender colored, with white lips; the aperture of the flower is nearly occluded by the arched lower lip. Like the other beardtongues/penstemons the tubular flowers have an upper and lower lip have a total of five lobes (two above, three below). The calyx, flower stems, and the flowers themselves are densely covered by glandular hairs; the stems are densely covered with fine white hairs. The stem leaves are pointed, triangular with toothed margins, and occur in opposite pairs; the leaf pairs are oriented at 90° to the pairs above and below them on the stem.

Penstemon

Penstemon hirsutus

hairy beardtongue [Blooms: May-Jul]

Pale beardtongue stems terminate in a 4-10" long panicle of flowers that is longer than broad. Flowers are 3/4" long consisting of a short, green calyx with five teeth, a tubular, white corolla similar to that of other penstemons/beardtongues, four fertile stamens with brown anthers, a bright yellow "beard" on the lower lip (as in hairy beardtongue), and a single style. The upper lip of the corolla has the usual two erect lobes, but the lower lip has three rounded lobes that project forward well beyond the margin of the upper lip. The outer surfaces of the flowers and flower stalks are covered with hairs. The throat of the corolla's lower surface has three thin purple veins, a narrow patch of long, bright yellow hairs, and a pair of low ridges/grooves, one on either side of the midline. The fruit is an egg-shaped capsule 1/4" long nestled in the persistent calyx. Both pale beardtongue and foxglove beardtongue (Penstemon digitalis) have white flowers and might be confused. However, the flowers of pale beardtongue are smaller, the flowers have two distinct ridges on the interior of the lower half of the corolla, and the three lobes on the lower lip are parallel to the floor of the corolla and extend well beyond the upper lip. None of these traits are present in foxglove beardtongue. In Jackson Park, pale beardtongue is less common than hairy beardtongue and much less common that foxglove beardtongue.

Penstemon

Penstemon pallidus

pale beardtongue [Blooms: May-Jun]

Ditch stonecrop is native to North America; its range includes the majority of the states in the U.S. and the provinces in Canada. It is a small (1-2' tall) plant with green or red stems, usually unbranched. Cymes of flowers 1-3" across arise from the upper stems, each cyme with 2-4 spreading flowering stalks; flowers are restricted to only one side of the flower stalks. Individual 1/4" flowers are yellowish-green to white, have five spreading, green sepals, ten stamens with cream-colored or yellow-orange anthers, and five beaked carpels, each with a single style and a green stigma; petals are completely absent. (The carpels look rather like a teapot with no handle and a very wide spout, or like a "duck" wine decanter. Look it up.) The carpels become the seed capsules; they turn bright red when mature. Ditch stonecrop prefers wet habitats (like ditches). It is completely unrelated to biting stonecrop (Sedum acre).

Penthorum

Penthorum sedoides

ditch stonecrop [Blooms: Aug-?]

At the apex of the stems and branches of wild dill are compound umbels of small white flowers; the umbels are about 6" across and have 12 umbellets that are widely spaced from each other. An umbellet is about 1" across and contains 7-21 flowers. Individua flowers are about 3 mm (1/8") across, consisting of 5 small, triangular, green sepals; 5 petals, each notched at the tip; (ideally) 5 stamens with white anthers; and a hairless ovary formed from two fused carpels, each with a short style. The stamens are fragile and often fall off, so there may be less than five stamens present. The fruit is an elongated schizocarp 3-5 mm long with a longitudinal groove that splits to release laterally flattened, wingless, brown to black seeds. Often, the remnants of the styles persist at the apex of the fruit.

Perideridia

Perideridia americana

wild dill [Blooms: Jun]

Waterpepper is a rather spare plant, 1-2' tall which needs close observation to be appreciated. 2-7" long spikes of minute flowers, only a few of which are open at any one time, terminate the upper stems; the flower spikes often nod or droop. Each greenish-white flower is ~1/8" long with five tepals covered with glandular pits (see below), green towards the base, brilliant white at the tips, 4-6 white stamens, and 2-3 white styles. The flowers never open very far. P. hydropiper is distinguished by (usually) reddish stems and the presence of tiny glandular pits (often pale yellow or brown, and only visible with magnification) on the greenish portions of the tepals. Cultivated varieties of waterpepper have been eaten in Japan and Europe, but the wild form produces a variety of oils that can cause skin (including the oral mucosa) irritation and swelling.

Persicaria

Persicaria hydropiper

waterpepper [Blooms: Aug-Sep]

Pale smartweed is a very tall smartweed (2.5-4') characterized by long, dense, drooping, whitish flower clusters and the absence of bristles on the leaf sheaths (ocreae). Stems terminate in drooping flower spikes 2-8" long, densely packed with small (1/8" long) flowers. Individual flowers have 4-5 greenish-white to pinkish tepals, 5-6 stamens with pink anthers and two styles. Because the flowers open only at their tips, the reproductive structures are difficult to observe. After fertilization, a three-angled seed, 2 mm across, develops nestled in the tepals. This is the largest smartweed that occurs in Illinois. Pale smartweed prefers wet soils (e.g., the shores of water bodies). Pale smartweed is similar to Pennsylvania smartweed (Persicaria pennsylvanica) but that plant has erect, cylindrical flower spikes and the flowers are pink or reddish.

Persicaria

Persicaria lapathifolia

pale smartweed [Blooms: Jul-Oct]