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Weeping willow is an exotic, probably originally bred in Asia or Europe. It is not very cold tolerant, so most "weeping willows" growing north of Kentucky or Virginia are actually hybrids. The aesthetically delightful "weeping" forms with yellow branches (the "golden" variety) are most likely a hybrid of Salix babylonica and Salix alba. There are separate male and female inflorescences in the form of catkins; each tree only produces one sex of catkins. The male catkins are 1-2" long and have no petals — only a series of stamens with white filaments and large (usually yellow) anthers. The female catkins are smaller (1" or less) and less showy with a series of green floral bracts that look like a series of awnings over 2-4 styles with flat stigmas; after fertilization they produce a green to brown capsule that releases cottony seeds.

Salix

Salix babylonica

weeping willow [Blooms: Apr]

Missouri River willow is dioecious — male and female florets (in the form of spike-like catkins) occur on separate plants. Catkins arise on one-year-old branches at about the same time as the leaves begin to emerge. Male catkins may be 1/2-2" long; each floret has two stamens with yellow anthers on their tips. Female catkins range from 3/4-2.5" long; the florets are yellowish-green and vase- or flask-shaped with an inflated base and a long beak that has a single protruding style. Both male and female catkins have a very small brown or bicolored bract at their bases that is covered with long, white hairs. After fertilization, female florets elongate as the catkin also elongates; the fruit is a yellowish to reddish green, hairless capsule, generally pear-shaped with a long beak. On maturity, the capsule splits to release seeds with long, attached, cottony hairs.

Salix

Salix eriocephala

Missouri River willow [Blooms: Apr]

Prairie willow is dioecious — plants produce either all male or all female inflorescences in the form of short catkins produced from one-year-old branches before the leaves emerge; a tiny black or bicolored bract covered in long, dense white hairs is present at the base of both male and female catkins. The florets lack both sepals and petals but both have a basal, hairy bract (regardless of sex). Male catkins are 1/4-1.25" long, elongating as they mature. Initially the male catkins are silvery (from long hairs) but become yellow or reddish from the numerous anthers. Individual male florets consist of a hairy, basal bract and a pair of stamens with cylindrical anthers initially purple, turning yellow, red, or orange. Female catkins are 1/2-3" long, also elongating as they mature. Individual female florets consist of the hairy bract and a hairy green ovary 4-8 mm long with an elongate beak densely covered with wooly hairs; a pair of stigmas protrude from the tip. After fertilization, the female florets transform into 1/4-1/2" long capsules, light brown at maturity, that split in two to release seeds surrounded by long, cottony hairs.

Salix

Salix humilis

prairie willow [Blooms: Apr-May]

Narrowleaf willow is dioecious — plants produce either all male or all female inflorescences (catkins) with the florets (male or female) spiraling around the catkin axis in a pseudo-whorl. Catkins are produced on one-year-old branches at the same time the leaves emerge. Male catkins are cylindrical, 3/4-2" long; they may be either erect or lean to one side but generally are ascending. Female catkins are also cylindrical, 1.5-3" long, initially green but turning light brown on maturity; they are usually terminal spikes on the new season's growth. Individual male florets consist of a single yellow, silky-hairy, oblong bract (quickly shed) and a pair of stamens with bright yellow anthers; the lower parts of the filaments are also covered by silky hairs. Individual female florets also have an oblong, basal bract that is shed; above that is a 1 mm long slender stalk supporting a bottle-shaped ovary 5-9 mm long with a pair of flat stigmas at its apex that appear to be four. After fertilization, the catkin elongates, and the ovary develops into a capsule that splits longitudinally to release the seeds when they are mature.

Salix

Salix interior

narrowleaf willow [Blooms: Apr-Jul]

Black willow is dioecious — plants produce either all male or all female inflorescences (catkins) on one-year-old branches; the catkins emerge with the leaves. Male catkins are 1-3" long, cylindrical, yellow to greenish-white, and usually curved. Female catkins are greenish are 1-3" long, elongating as they mature. Both male and female florets are numerous and arranged in pseudo whorls around the axis of their respective catkins; neither has either sepals or petals. Individual male florets have 3-6 stamens with yellow, globose anthers and a pale yellow, oval basal bract shorter than the stamens. Individual female florets also have a pale yellow, oval basal bract; a hairless, flask-shaped pistil 3-5 mm long is elevated above the bract on a 0.5-1.5 mm long (short!) pedicel and has a single style and a pair of stigmas at its tip. After fertilization, a capsule enlarges, finally splitting longitudinally to release the seeds with their attached cottony hairs.

Salix

Salix nigra

black willow [Blooms: ??]

On black snakeroot, one to five 1/2" wide globoid umbels (flower clusters) arise from the tips of the upper stems. Each umbel is packed with 20-60 tiny flowers and their flower stalks (pedicels). In each umbel, 1-3 flowers are "perfect" (with both male and female organs) and the rest are staminate (stamens only). In addition to the male stamens, the perfect flowers have two long, cylindrical styles (emerging from a hidden ovary) that arch and recurve from the middle of the flower; the styles are much longer than the hooked bristles on the ovary. Both staminate and perfect flowers have a minute (<1 mm) green calyx with five rounded teeth, five dull yellow to greenish-yellow, heart-shaped petals (tip of the heart towards the center of the flower), and five protruding stamens <3 mm long with obvious yellow (or brown) anthers. The fruit is a 1/4" long round to cylindrical bur covered with short, hooked bristles; the remains of the styles often persist. The bur splits to release the two seeds inside.

Sanicula

Sanicula odorata

black snakeroot [Blooms: May-Jun]

At the tip of the culm, dark green bulrush produces an inflorescence comprised of one to three (rarely four or five) compound umbels of spikelets; beneath the inflorescence are 3+ leafy bracts (similar to the leaves) that are up to 1' long and 1/2" wide. At least one of the bracts is always longer than the inflorescence. The umbels generate 1/4-4" long, straight branches in all directions that terminate in umbelletes of 5-20 spikelets that rest on slender, leafy bractlets; the spikelets may be sessile or may rest on 1/2" long branchlets. The branches and branchlets are green, straight, and stiff. Spikelets are less than 1/4" long (3-6 mm), ovoid or egg-shaped, yellowish green initially but darkening to brown or black later; the spikelets are an assemblage of numerous spirally arranged, overlapping scales and their florets. The florets each have a single subtending scale, three stamens, and an ovary with a tripartite style; they are wind pollinated. Bulblets may form on one or more branches and sprout late in the season. The umbels may be visually dense and complex and take some study to sort out.

Scirpus

Scirpus atrovirens

dark green bulrush [Blooms: May-Jul]

The tips of the upper stems of common groundsel produce dense clusters of flowerheads on short peduncles; inflorescences can also arise from leaf axils. Common groundsel flowerheads are cylindrical, 8 mm long and 4 mm across, with black-tipped, green bracts around the outside at both the base and the apex and 13-80 yellow disc florets peeking out the end; mature flowerheads are easily mistaken for flower buds. The disc florets have tubular yellow corollas, five stamens fused to the upper part of the corolla with yellow-brown anthers, and a bifurcated style with purplish stigmas. There are no ray florets. This is an easy plant to overlook. The flowerheads are twice as long as wide. The seedhead looks like a compact dandelion tuft with seeds on parachutes of light brown hairs.

Senecio

Senecio vulgaris

common groundsel [Blooms: May-Jul]

The five petals and five sepals of Maryland senna's 3/4" flowers are both yellow. The single pistil has many spreading white hairs and arches upward. The anthers of the 10 stamens are a striking dark brown (like partridge pea). The upper three stamens have short filaments and short anthers that produce only sterile pollen (as a pollinator reward). The middle four stamens have short filaments and long anthers while the lower three stamens have long filaments and long anthers; all seven of these stamens produce fertile pollen that is released by "buzz pollination." The flowers do not produce nectar. The fruit is a flattened seedpod 1/2" across and 3-4" long with 10-18 segments, each containing a single 1/4" flattened seed.

Senna

Senna marilandica

Maryland senna [Blooms: Jul]

Flower buds arise singly or in small groups on 1/2" long peduncles from the leaf axils. Because the flower peduncles are shorter (1/2") than the leaf petioles (1"), the flowers are often partly hidden among the leaves. Individual flowers are about 8 mm across. A flower contains five green, triangular sepals; five light yellow or light orange, rounded, floppy petals with pale lines that function as nectar guides and asymmetrical tips; and a central reproductive column (like mallows, to which prickly sida is related). That column consists of five styles fused along most of their lengths, each with a globose terminal stigma, and numerous stamens with yellow anthers. After fertilization, a circular seedpod forms from the five carpels; when mature, the seedpod turns brown and breaks into five segments, each containing a single reddish-brown, three-angled seed.

Sida

Sida spinosa

prickly sida [Blooms: Aug-Sep]

Compass plant flower stalks are very hairy, have scattered sessile, triangular bracts, extend vertically multiple feet, and bear 3-4" yellow, sunflower-like composite flowers. There are 20-35 yellow ray florets (e.g., petals) and 100-200+ yellow, tubular disk florets. Behind the flowerheads are two or three layers of very hairy, green, lance-like bracts with sharply pointed, recurved tips. For unknown reason (it just IS), only the ray florets are fertile; the disc florets bear only functional stamens (with a non-functional style protruding through the middle of the stamen). (True throughout the genus Silphium. The opposite is true in the sunflowers, genus Helianthus, where the ray florets are functionally male and the disk florets are fertile, functional females.)

Silphium

Silphium laciniatum

compass plant [Blooms: Jun-Sep]

Prairie dock's hairless flower stalks produce a panicle of buds and flowerheads. The flowerheads are 2-3" across, with 15-30 bright yellow ray florets with pointed tips and two grooves running the length of the petals; a yellow central disc about 1/4-1/3 the width of the flower contains 120-140 disk florets, green when still buds but bright yellow when open. Behind the flowerhead are two or three layers of green, egg or teardrop shaped, hairless bracts. The ray florets have a bifurcated but functional style protruding from a short yellow tube at the base of the petal; the disc florets have tubular corollas with a non-functional style protruding through the stamen. (True throughout the genus Silphium. The opposite is true in the sunflowers, genus Helianthus, where the ray florets are functionally male, and the disk florets are fertile, functional females.)

Silphium

Silphium terebinthinaceum

prairie dock [Blooms: Jun-Sep]

Wild mustard's upper stems end in racemes of 1/2" wide yellow flowers. Each flower has four yellow petals, six yellow stamens, and a single green pistil. After fertilization, the pistil elongates into a thin, cylindrical silique (seedpod), 1/2-1.5" long, filled with tiny (2 mm diameter) brown or black seeds; the distal third of the silique is a ridged or square "beak". The seeds are reported to remain dormant but viable in the soil for up to 60 years.

Sinapis

Sinapis arvensis

wild mustard [Blooms: May-Jun]

Hedge mustard flowers occur at the tips of long, slender flower stalks that curve upward; the flower stalks typically arise in abundance at the top of the plant. Each flower is small (1/4" across) with four greenish-yellow sepals, four rectangular yellow petals with rounded tips, a single stout style, and six stamens. The fruit is a very slender, cylindrical seedpod (silique) lower on the flower stalk than the blooming flowers; the siliques are 3/8-3/4" long, erect, oriented parallel to and often appressed to the flower stalk, with the remains of the style on their tips. The siliques turn light brown when mature and split open to release the seeds. The short (<3/4"), straight, appressed seedpods and the upward-curving, sparse flower stalks with only a few blooms open at any one time distinguish hedge mustard from other local mustards.

Sisymbrium

Sisymbrium officinale

hedge mustard [Blooms: May-Jul]

Tall goldenrod flower clusters vary from pyramidal (at least as long as wide, the most common) to club shaped; the tip of the pyramidal form is often arched or nodding (like a bent topknot). The flowerheads are less than 1/4" across, have 8-15 yellow ray florets and 3-6 yellow disc florets; the base of the flowerheads have 2-3 layers of narrow, hairless, greenish bracts (phyllaries) always more than 3 mm long in total. The flowerheads are all attached on one side of the hairy floral stalks. The fruit is a dry seed with a tuft of white hairs (a pappus); it is 2.5-3.5 mm long. Tall goldenrod is difficult to differentiate from Canada goldenrod (S. canadensis) (both are three-nerved) but tall goldenrod has phyllaries longer than 3 mm while Canada goldenrod's phyllaries are always shorter than 3 mm. Some argue the two may be the same species, but tall goldenrod blooms later than Canada goldenrod. Both tall goldenrod and late goldenrod (Solidago gigantea) are three-nerved, have the largest leaves at mid-stem, and pyramidal inflorescences, but tall goldenrod has rough-feeling (sandpapery) stems and leaves while late goldenrod has smooth stems and leaves. Of the three very similar species (late goldenrod, tall goldenrod, and Canada goldenrod), only late goldenrod has a hairless stem.

Solidago

Solidago altissima

tall goldenrod [Blooms: Sep-Oct]

The axils of the middle and upper leaves of woodland goldenrod produce small clusters of 1-12 flowerheads; the stem tip may also develop a small (3" long, 1.5" across) panicle of flowerheads. Individual flowerheads are tiny (3 mm) consisting of 4-5 ray florets with yellow, oblong-elliptical "petals" and 3-6 disc florets with golden yellow, tubular corollas with five tiny lobes. At the base of each flowerhead are three overlapping series of light green, elongate-elliptical bracts (phyllaries). The fruit is a small, bullet-shaped seed 1-2 mm long with a tuft of white hairs 3-5 mm long. In Illinois, only woodland goldenrod and broad-leafed goldenrod (Solidago flexicaulis) produce clusters of flowerheads from the axils of the middle and upper leaves; however, the latter has coarsely serrated leaves with petioles and should be easy to distinguish from woodland goldenrod.

Solidago

Solidago caesia

woodland goldenrod [Blooms: Sep-Oct]

A panicle of flowering stems develops at the top of a Canada goldenrod plant; the flowering stems arch away from the main stem, their upper sides covered with yellow flowers. The panicle may be pyramidal (at least as long as wide) to spreading (wider than long); it is sometimes club-shaped on smaller plants. Individual flowers are 1/8-1/4" across, with 8-14 yellow ray flowers and 3-6 yellow disc flowers. The base of the flower is surrounded by 3-4 layers of narrow, hairless, green bracts (phyllaries); the entire set of phyllaries is two to less than three millimeters long. The flower stalks (pedicels) are hairy, about as long as the set of phyllaries, and curve upwards. The fruit is a dry, ribbed seed 1-1.5 mm long with a tuft of white hairs 1.8-2.2 mm long. Canada goldenrod is difficult to differentiate from tall goldenrod (S. altissima) (both are three-nerved), but tall goldenrod has phyllaries longer than 3 mm while Canada goldenrod's phyllaries are always shorter than 3 mm. Some argue the two may be the same species but tall goldenrod blooms later than Canada goldenrod. Of the three very similar species (late goldenrod, tall goldenrod, and Canada goldenrod), only late goldenrod has a hairless stem.

Solidago

Solidago canadensis

Canada goldenrod [Blooms: Jul-Oct]

The tip of broad-leaved goldenrod's stem produces a cylindrical inflorescence (a raceme or a narrow panicle) 1.5-5" long and about a third as wide; smaller racemes (1/2-1.5" long, smaller than the leaves) arise from the axils of the upper leaves. Individual flowerheads are about 1/4" across with 3-4 yellow ray florets asymmetrically deployed around the flowerhead and 4-8 yellow disk florets. The base of the flowerhead is surrounded by 3-5 series of unequal, narrowly oblong, light green phyllaries; the outermost phyllaries are 1-2 mm long while the innermost are 3.7-4.7 mm long. Broad-leaved goldenrod prefers high-quality, moist, shaded woodlands. In Illinois, only broad-leaved goldenrod and woodland goldenrod (Solidago caesia) produce clusters of flowerheads from the axils of the middle and upper leaves. Broad-leaved goldenrod has unusually large flowers for a goldenrod and the ray florets are not evenly distributed around the flowerhead. In addition, woodland goldenrod has smooth or finely serrated leaf margins (rather than coarsely-toothed leaves) and no petioles (the leaves are sessile) — it should be easy to distinguish from broad-leaved goldenrod.

Solidago

Solidago flexicaulis

broad-leaved goldenrod [Blooms: Jul-Sep]