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in common spike-rush, at the tip of the culm is a single spike, elongate-ovoid with a sharply pointed tip, up to about 1" long; 30-100 florets ( each with three stamens bearing dark yellow anthers and a split style) are spirally arranged around the spikelet, each protected by a pointed scale 3-5 mm long. The scales have a green to straw-colored midrib, reddish- or orange-brown flanks, and a translucent edge. The two lowest scales in the spike lack flowers. The lowest scale wraps less than 3/4 of the base; it is mostly green bordered by a brown band and a translucent, rounded edge and is more leathery than other scales.

Eleocharis

Eleocharis palustris

common spike-rush [Blooms: May-Jul]

Jerusalem artichoke should rightly be called a "sunflower" like the other four members of the genus Helianthus present in Jackson Park. Five to fifteen flowerheads ride on hairy peduncles up to 8" long and are 2.5-3.5" across; each is cupped by 2-3 overlapping series of phyllaries (bracts) that are more triangular than lance-shaped, hairy, and sharply pointed. The flowerheads consist of 10-20 sterile, yellow ray florets; the 60+ fertile disc florets consist of tubular yellow corollas about 1/4" long with five lobes at their apex and five protruding brown or black anthers fused around a yellow style with a bifurcated stigma. Jerusalem artichoke was cultivated by the indigenous peoples of the midwest for its tasty and carbohydrate-rich tubers.

Helianthus

Helianthus tuberosus

Jerusalem artichoke [Blooms: Aug – Oct]

Duckweed is a tiny, floating flowering plant (one of the smallest in the group) that is present on the lagoons and Columbia Basin from May through October. The flower is highly reduced — about 1 mm across consisting of a cup-shaped scale, a pair of tiny stamens, and a single pistil; I have never observed it. (The flowers are rarely produced — most reproduction is vegetative.) The combination leaf and stem is oval, 2-5 mm long and 1.5-3.5 mm across with a single rootlet up to 2 cm long dangling from the underside. Unless you have a good magnifying glass or microscope, further detail will not be useful.

Lemna

Lemna minor

duckweed [Blooms: ?]

Lyme grass flower spikes are 5-14" long, initially blue-green or silvery but turning beige when mature. There are typically one pair of spikelets per node on the spike. The spikelets are 1/2-1" long, containing 2-5 (typically 3) florets; each floret contains two bottlebrush-like styles and 1-3 stamens, each typically with a single yellow anther. Like all grasses, Lyme grass is wind pollinated. Lyme grass is very similar to the native American dune grass (Leymus mollis) but the latter is greener and is finely hairy under the spike. Lyme grass has become established in sandy habitats around the Great Lakes and (curiously) along the coast of Greenland.

Leymus

Leymus arenarius

Lyme grass [Blooms: May-Jun]

Wild chamomile stems terminate in a daisy-like flowerhead, 1-2" across. Flowerheads consist of 10-25 white, fertile (pistillate) ray florets that tend to droop slightly and a gumdrop-shaped central mass of 250-550+ yellow disk florets with both male and female reproductive structures. Individual disk florets are tubular. Behind the flowerhead are one to three series of light green, lance-shaped bracts with membranous edges. Wild chamomile can be distinguished from similar plants like ox-eye daisy (Leucanthemum vulgare) by its multiply-pinnate, slender lobes leaves and the fact that the flowerhead is actually hollow; when crushed they produce a pleasant, fruity fragrance. Wild chamomile is closely related to pineapple weed (Matricaria discoidea) but the two can't be confused.

Matricaria

Matricaria chamomilla

wild chamomile [Blooms: May-Jun]

Hop hornbeam (aka, ironwood) flowers are in the form of catkins, with separate male and female inflorescences. Male (staminate) catkins are 1-2" long, narrowly cylindrical, often occurring in groups of three; male flowers have three stamens. Female (pistillate) catkins are 1/2" long and stubby, occurring singly at the tips of branches; individual flowers consist of a basal, green bract and two red, thread-like styles. The flowers are wind-pollinated. The fruit is 1.5-2.5" long and 3/4-1" wide, superficially similar to the fruit of hops vines (Humulus lupulus), with flattened, spindle-shaped nutlets 5-8 mm long hidden inside yellowish, papery, inflated sacs 1/3-1" long.

Ostrya

Ostrya virginiana

hop hornbeam [Blooms: Apr-May]

Reed canary-grass is a very widespread species (the native range is circumboreal in the Northern Hemisphere) that is listed as "vulnerable" in Illinois. It is a wetland grass that reaches heights of 3-5 feet; plants tend to be widely spaced on Jackson Park although they are known to produce clonal colonies elsewhere. The leaves are flat, alternate, and evenly spaced along the culm. The leaf blades reach up to 12 long and 3/4" across; they are green or blue-gray and hairless with continuous (but rough-textured) margins. The leaf base is much wider than the culm (stem) which it clasps tightly; the leaf sheaths look like an extension of the leaf in both color and appearance. When reproductive (early-midsummer), the culms produce a narrowly-pyramidal panicle up to 10" long and 2-3" across of spikelets that bear the florets. Spikelets are initially green but fade over time to a light tan color. The stem and leaves all turn a diagnostic light tan during the late fall and winter; the leaves mostly remain attached.

Phalaris

Phalaris arundinacea

reed canary-grass [Blooms: May-?]

Giant reed is a grass that grows 4-16' tall (the tallest native grass in Illinois), often in dense, clonal stands. The culm (stem) is greyish-blue or light green; the base of the culm may be 15 mm (about 5/8") across. The culm ends in a panicle up to 1.5' long and half as wide of spikelets. When the florets are blooming, the panicle of spikelets has a reddish, silky appearance. Each spikelet is 12-17 mm long containing 3-7 florets. At the base of the spikelet is a pair of scale-like glumes (bracts) at about a 30° angle to each other; the base of the upper glume is nested inside the base of the lower glume, and both have a long, tapered, pointed tip. The glumes are typically 4-6 mm (1/4") long. Above the glumes, along the central axis of the spikelet (rachilla) are a series of progressively-shorter bracts (lemma and palea — more delicate versions of glumes — surrounding each floret) and tufts of silky hairs 1 cm long attached to the rachilla and obscuring the florets. The most basal floret is either sterile or is staminate; the remaining florets containing both male and female reproductive organs (= "perfect"). Staminate and perfect florets contain 1-3 stamens with purple anthers; perfect florets also have two long, feathery styles. The florets are wind-pollinated. After fertilization, individual seed grains replace the florets.

Phragmites

Phragmites australis

giant reed [Blooms: ?early-midsummer]

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]

Male and female flowers of pin oakare spatially separated but often occur on the same branch. Female flowers have been reduced to only a short, green spike bearing three bright red styles; the female flowers emerge from leaf axils and may occur in clusters of up to three. The male flowers are borne on 1.5-4" long green catkins that dangle from bud clusters at the tip of the previous year's growth. The fruits are egg-shaped or elliptical (hence the species name) acorns 1/2-2/3" long with a deep reddish cap that covers about half the acorn.

Quercus

Quercus ellipsoidalis

Northern pin oak [Blooms: Apr–May]

In bur oaks, both male and female flowers are produced on the same tree, but they are widely separated; the flowers are wind pollinated. Male flowers are borne on drooping, yellowish-green catkins 2-5" long that hang from the tips of the previous year's twigs; individual male flowers consist of 5-20 stamens surrounded by a lobed calyx. Some sources (e.g., http://www.missouribotanicalgarden.org/plantfinder/PlantFinderDetails.aspx?taxonid=280704) assert that the female flowers of bur oak also occur on catkins, but this is incorrect. Instead, the female flowers occur alone or in groups of 2-3 that arise in the leaf axils of new leaves. Individual female flowers are about 3 mm (1/8") long; a short, reddish green stalk (a pistil) covered with appressed scales bears naked reddish-green or light green styles on its tip. The female flowers are wind pollinated. Both male and female flowers form after the leaves begin to unfurl; the male catkins precede the female flowers by one to several weeks. Fertilized female flowers produce one or two acorns; the acorns may be nearly sessile or hang from short (<1") stalks. Mature bur oak acorns are 1.5-2.5" long and the same across (including the caps) — they are the largest acorn of any oak. The caps (= cupules) cover at least half of the length of bur oak acorns, often so much that only a nubbin of the acorn is visible. The caps are covered with coarse scales that have an obvious keel and appear knobby; the marginal scales on the caps bear soft awns up to 8 mm (1/3") long that form a conspicuous fringe above the acorn — this is the "bur" that is referred to in the common name in analogy to the machine tool used for grinding. The acorns mature and germinate over a single summer; they do not need to be exposed to cold to germinate.

Quercus

Quercus macrocarpa

bur oak [Blooms: Apr–May]

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: ??]

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]