The composites are often considered to be the largest or second largest family of flowering plants in the world, with perhaps 20,000 or more species. Many are known as ornamentals. Only a few provide human food, e.g., in this part of the world, lettuce, artichokes, and sunflower (for oil). Low levels of toxins or at least bitter substances occur in many of these plants. Successfully noxious weeds abound.
The family is easily recognized by its involucrate heads. Close beneath the clusters of flowers (florets) comprising a head are few to many bracts making up an involucre (which is to the head much as the calyx is to a single flower in other families). The individual bracts of the involucre are called phyllaries (or in some works, tegules). Radially symmetrical flowers, as massed in the center of a daisy or sunflower or as seen with long slender corolla lobes in a thistle, are disk flowers and make up the disk. Surrounding them in some species are petal-like flowers, bilaterally symmetrical, called ray flowers, and heads with both kinds of flowers can be called radiate; those lacking rays are discoid. Ray flowers are sometimes also called ligulate, especially in the tribe in which all heads consist entirely of such ligulate flowers. The central flowers in such heads, as the last to open, may appear radially symmetrical while still in bud, as in the common dandelion, but should not be mistakenly interpreted as disk flowers. In some species, the ray flowers are sterile (lacking a functional pistil); in others, they are pistillate. Disk flowers are usually bisexual, but there are exceptions, especially in dioecious species (where, e.g., functionally staminate flowers may have only rudimentary styles).
The term “ray” generally refers to the expanded, petal-like part of a ray flower, and is to be so interpreted when ray measurements and colors are stated in the keys and text. Since the number of rays necessarily equals the number of ray flowers, the term is also often used when a count of ray flowers is intended. “Double” forms in some species, with only rudimentary reproductive parts and all flowers converted to rays, such as the goldenglow of the garden (Rudbeckia laciniata cv. Hortensia), may be found occasionally as escapes from cultivation and may be falsely thought to belong in “Group A,” in which the ligulate flowers are all bisexual.
Measurements of the length of the involucre are from its base to the tip of the longest phyllaries. As in other circumstances, measurements should be made on mature structures.
The ovary of each individual flower is inferior. Surrounding the base of the corolla, or on the summit of the achene, may be a ring of tissue, a series of bristles, two or more scales or awns, or some combination of such structures. These constitute the pappus, of which the ancestral structure was apparently a calyx. Pappus characters are very helpful in classification and identification. Often the pappus is an important seed-dispersal device. On the receptacle, to which the flowers of a head are attached, there may be chaff: scales or bristles, short or long, also useful in classification and identification. Beginners must take care to remember that chaff is on the receptacle, and the pappus is at the summit of the ovary (and of the achene into which the ovary ripens). The stamens are normally united in a ring around the style (in Iva, Ambrosia, and Cyclachaena of our flora, the anthers are separate). Beginners should also be warned not to confuse the ring of anthers inside or protruding from a disk corolla with the corolla itself.
The individual fruits are here called “achenes.” Some authors prefer the specialized term cypsela for the peculiar fruit of the Asteraceae, derived from a 2-carpellate, inferior ovary, and reserve “achene” for a fruit of similar texture but derived from a single superior carpel (as in many Ranunculaceae and Rosaceae).
Just as spikelets in the grass family are usually more than single flowers, so also are heads in the Asteraceae. Nevertheless, it is often convenient, as in the grasses, to use the word pedicel to refer to the stalk of a single head (the florets of which are never stalked) and to use the regular terms that describe inflorescences when describing the arrangement of heads: e.g., spicate, racemose, corymbose (although variant terms like corymbiform or paniculiform can be used). When both “pedicel” and “peduncle” are used, the latter refers to the stalk of a group of heads. The term scape (or sometimes peduncle) is used to refer to a leafless stalk (above the basal leaves) bearing one or more heads at the summit.
KEY TO GROUPS A, B, C
1. Heads entirely of flat ligulate flowers (these all bisexual); sap milky; leaves alternate or basal (never opposite).
1. Heads all or partly of regular disk flowers (sometimes thread-like, sometimes very deeply lobed); ligulate (ray) flowers sterile or pistillate and only around the margin of the head; sap watery; leaves various (opposite in some species).
2. Pappus none or entirely of scales, teeth, flattened spines, or few (up to 8) stiff awns.
2. Pappus all or primarily of numerous long soft hairs or bristles (or these rising from scale-like bases in Dyssodia, or 2 long bristles and numerous tiny ones in Boltonia).
KEY TO GENERA OF GROUP A
1. Pappus none or a crown or entirely of scales (without separate bristles).
2. Leaves all basal.
3. Pappus none; scapes gradually enlarged from base to summit; involucres, scapes, and leaves without distinctly longer hairs.
3. Pappus present (only as scale-like crown on outermost achenes; of long hairs on inner achenes); scapes at most slightly enlarged beneath the head; involucres, scapes, and especially leaves with distinctly longer hairs minutely forked at the tip.
Leontodon (in part)
2. Leaves all or partly cauline.
4. Flowers blue (rarely white or pink), in heads 3–4.5 cm broad; pappus of numerous tiny scales; cauline leaves sessile; phyllaries (at least the outer ones at maturity) nearly always with few to many gland-tipped hairs.
4. Flowers yellow, in heads ca. 1 cm or less broad; pappus none; cauline leaves (below inflorescence) tapered to a petiolar base; phyllaries glabrous or nearly so.
1. Pappus at least partly of bristles or soft hairs.
5. Pappus composed of both scales and bristles (scales may be short and inconspicuous); involucre a single series of phyllaries.
5. Pappus composed entirely of hairs or bristles; involucre various.
6. Pappus at least partly of plumose bristles.
7. Plants with leaves in a basal rosette, the stems (simple or branched) at most with very reduced bracts.
8. Receptacle with a ± membranous scale subtending each flower and achene and bearing an elongate bristle-like tip (evident even among the flowers, and equaling the pappus); achene with a slender beak longer than the body; involucre 11–16 mm long (or even 25 mm in fruit), the phyllaries glabrous or (usually) with few to many bristles on the midrib only.
8. Receptacle without scales or chaff; achene beakless; involucre ca. 7–10 (–14) mm long, even in fruit, the phyllaries glabrous or ± hairy all across.
9. Stem usually branching, with a few heads on long pedicels; hairs all simple, not forked; outermost achenes in head with pappus of one row of plumose hairs, as in the other achenes.
9. Stem simple, the heads on naked scapes; hairs (especially those on the leaves) minutely 2 (–3)-forked at the apex [30–40×]; outermost achenes in head with pappus solely of scales, the other achenes with pappus of plumose hairs surrounded by short simple hairs.
Leontodon (in part)
7. Plants with leaves of fertile stems all or partly cauline.
10. Leaves with prominent midrib and lateral veins; stems, leaves, and involucres with scattered stiff hairs; achenes beakless, the pappus readily deciduous; phyllaries imbricate.
10. Leaves parallel-veined (even the midrib scarcely if at all more prominent than other veins); stems, leaves, and involucres glabrous (or when young with a little loose tomentum); achenes very long-beaked, the pappus persistent with intertangled plumose bristles, the whole head spherical at maturity; phyllaries in a single series.
6. Pappus entirely of simple bristles or hairs (at most barbed or scabrous).
11. Heads solitary on completely naked scapes; leaves all in a basal rosette; scapes glabrous or with a little loose tomentum.
12. Phyllaries in 1 series or irregularly imbricate; achenes antrorsely hispidulous, with beak less than half as long as the body; leaves entire (or with an obscure occasional denticulation).
12. Phyllaries in two definite series, the outer ones strongly spreading or usually recurved; achenes tuberculate or spiny toward summit of body, with elongate slender beak; leaves ± toothed or pinnatifid.
11. Heads (1–) 2–several on naked to leafy stems; leaves basal or cauline; scapes on 1-headed plants rather densely pubescent with stellate and/or long straight hairs.
13. Leaves all or mostly in a basal rosette at flowering time (or on stoloniferous basal shoots), entire and unlobed.
Hieracium (in part)
13. Leaves all or mostly cauline at flowering time, entire or toothed or lobed, or if largely basal, then toothed.
14. Involucres cup-shaped or bell-shaped, at least two-thirds as broad as long at anthesis; achenes scarcely if at all beaked.
15. Cauline leaves tapered to base or sessile but not auriculate-clasping; pappus light to darkish brown.
Hieracium (in part)
15. Cauline leaves (at least the upper ones) ± auriculate or clasping at the base; pappus pure white, copious.
16. Leaf margin not spiny; involucre 5.5–9.5 (–10) mm long; achenes ± terete (but ribbed).
16. Leaf margin prickly with prolonged ± spiny-tipped teeth; involucre ca. 8–18 mm long at maturity; achenes at least somewhat flattened.
14. Involucres (at least at anthesis) cylindrical to urn-shaped, at least twice as long as broad; achenes long-beaked, short-beaked, or beakless.
17. Cauline leaves less (usually much less) than 1 cm broad, entire to denticulate, readily deciduous; body of achene spiny at apex (as in Taraxacum) and bearing a long slender beak.
17. Cauline leaves broader or if less than 1 cm then entire and persistent; body of achene smooth or only ribbed, beakless or beaked.
18. Blades of cauline leaves (in outline) less than twice as long as broad, entire or with lobes 3 (–5) and somewhat palmate in aspect (or involucre hairy); achenes neither flattened nor beaked.
18. Blades of cauline leaves (in outline) over three times as long as broad, entire or with lobes 5–7 and clearly pinnate; involucres glabrous; achenes strongly flattened, beaked (usually) or not.
19. Florets 5 per head; longer phyllaries 5 or fewer.
19. Florets and phyllaries more numerous.
20. Middle and upper cauline leaves all or mostly toothed and lobed; plant annual or biennial.
20. Middle and upper cauline leaves entire, unlobed; plant a deep-rooted perennial.
KEY TO GENERA OF GROUP B
1. Involucre of just 2 series of phyllaries distinctly different in size, texture, and/or orientation; heads at least 1 cm broad; cauline leaves opposite or whorled.
2. Leaves all or mostly aquatic (submersed), apparently whorled, fully dissected with filiform segments (usually at least 1 pair of simple, opposite, toothed leaves on emersed stem beneath head); heads radiate, 1–2 at the end of long leafy (submersed) branches; pappus awns elongating to 2 (–4) cm in fruit.
Bidens (in part)
2. Leaves not aquatic (if finely divided, nevertheless terrestrial); heads various; pappus awns, if any, less than 1 cm long.
3. Phyllaries of inner series (longer and easily seen) connate at least a third of their length; ray flowers none.
3. Phyllaries slightly or not at all connate; ray flowers present or not.
4. Pappus of distinct barbed awns.
5. Ray flowers none or clear yellow; leaves various (but narrowly lobed in only one species of wet places); native, common.
Bidens (in part)
5. Ray flowers red to white or orange; leaves deeply pinnately lobed into narrow or even filiform segments; rarely escaped into disturbed places.
Cosmos (in part)
4. Pappus of 2 teeth or scales or absent.
6. Leaves all cauline, unlobed, sessile and clasping; outer phyllaries equaling or exceeding the inner, the latter resembling the broad membranous receptacular chaff; disk flowers pubescent just above the ovary.
6. Leaves cauline and/or basal, unlobed (narrowly lanceolate), lobed, or compound, not clasping; outer phyllaries shorter than the firm inner ones; disk flowers glabrous.
7. Outer phyllaries various (often less than half as long as inner), at most barely connate at the very base; leaves various: simple, or palmately lobed or compound, or if pinnately lobed at least the central lobe usually much larger than the lateral ones; achenes strongly flattened, not beaked, in most species winged.
7. Outer phyllaries more than half as long as inner, clearly connate at the base (for ca. 0.5–1 mm above the receptacle); leaves deeply pinnatisect with uniformly narrowly lanceolate to filiform lobes; achenes little if at all flattened, beaked, without wing.
Cosmos (in part)
1. Involucre imbricate, with phyllaries of more than 2 lengths, or with a single series of phyllaries, or heads less than 1 cm broad; cauline leaves various.
8. Corollas very deeply lobed, the narrow linear lobes at least 4 mm long and about equaling the tube or longer; phyllaries (the middle ones if not all) with prominent fringed or lacerate margins, at least at their tips.
9. Heads apparently spherical (1-flowered heads in spherical secondary heads); pappus a distinct fringed crown; leaves densely white-woolly beneath.
9. Heads less than hemispherical; pappus none or of a few linear scale-like bristles; leaves not white-woolly beneath.
10. Phyllaries leafy, the margin merely spiny; leaves spiny; flower yellow or orange.
10. Phyllaries not leafy, lacerate or fringed at the tip (including a terminal spine or not); leaves without spines; flowers pink, white, or purple, yellow only in one waif.
Centaurea (Group C)
8. Corollas with shorter lobes if any; phyllary margins at most merely ciliate.
11. Margins of phyllaries with a well defined hyaline or scarious border at least around the tip; leaves alternate.
12. Receptacle, and hence the disk, conical or high-hemispherical, the disk (including florets) at least 6 mm broad at the base; leaves all deeply dissected.
13. Heads rayless; bruised plant with fruity (pineapple) aroma.
13. Heads with ray flowers; bruised plant with or without odor.
14. Ray flowers yellow.
14. Ray flowers white.
15. Receptacle with chaff (except around the marginal flowers in A. cotula); leaf segments and axis pubescent, often all or mostly ca. 0.5–2 mm broad, flat.
15. Receptacle without chaff; leaf segments mostly revolute-filiform, essentially glabrous, less than 0.5 mm broad.
16. Involucres ca. 2–3.2 mm long; pappus none; achene ribs 5, ± weak; plant aromatic when bruised.
16. Involucres ca. 4–5.5 mm long; pappus present (though minute); achene ribs 3, strongly thickened or wing-like; plant nearly or quite odorless.
12. Receptacle flat or slightly convex, the disk in some species less than 5 mm broad; leaves dissected or not.
17. Leaves unlobed (but closely and regularly toothed), glabrous or only slightly silky when mature.
18. Rays ca. 4–6 mm long; leaves not over 8 mm wide.
18. Rays over 10 mm long or absent; leaves over 10 mm wide.
19. Disk less than 1 cm broad; rays none; foliage sweet-smelling; heads numerous on very short pedicels.
19. Disk and conspicuous white rays each over 1 cm; foliage not aromatic; heads 1 to several on each stem or branch.
20. Leaves not glandular-punctate, with low rounded teeth; heads 1–2 on long peduncles.
Leucanthemum (in part)
20. Leaves glandular-punctate, with large acute teeth; heads several on each stem or branch.
17. Leaves lobed or dissected (or at least deeply toothed near base) or if unlobed then densely tomentose at least beneath.
21. Rays present, white.
22. Rays 1–3 mm long; receptacle chaffy with an elongate scale at the base of each floret.
22. Rays 4–50 (–65) mm long; receptacle without chaff.
23. Heads solitary on long stems, 3–5 (–6.5) cm broad; foliage scentless, the leaves shallowly once-pinnately lobed.
Leucanthemum (in part)
23. Heads several to many, less than 2 cm broad, ± corymbose; foliage strong-scented, the leaves bipinnatifid.
21. Rays absent or yellow.
24. Disk conspicuous (yellow), 5–22 mm broad (if less than 10 mm, then the leaves nearly glabrous); inflorescence ± corymbiform.
Tanacetum (in part)
24. Disk inconspicuous, usually less than 5 mm broad (if 5–10 mm, then the leaves densely tomentose beneath); inflorescence various.
25. Leaves deeply pinnatifid, the segments toothed; heads in a dense convex corymbiform inflorescence; heads with short yellow rays.
25. Leaves ± finely dissected, less commonly entire or merely serrate; heads in an elongate paniculiform inflorescence; heads discoid.
11. Margins of all or most phyllaries not hyaline or scarious (or if so, the leaves opposite); leaves opposite or alternate or all basal.
26. Heads without ray flowers.
27. Lower surface of leaves densely white-woolly (stem never spiny); corollas present.
27. Lower surface of leaves glabrate or, if densely pubescent, the hairs neither white nor woolly (if whitened in Xanthium spinosum, the stem spiny); corollas often absent on pistillate flowers.
28. Leaves all alternate; involucre of pistillate heads covered with hook-tipped spines, forming a beaked bur in fruit; staminate heads crowded immediately above the pistillate heads, with separate phyllaries.
28. Leaves (at least the middle and lower) opposite; involucre of all heads without hooked spines (at most with horn-like protuberances); staminate (or all) heads in a branched cymose inflorescence or in elongate raceme-like or spike-like inflorescences and the phyllaries united into a cup.
29. Inflorescence branched (cymose); phyllaries ca. 5 mm or more long, separate.
Polymnia (in part)
29. Inflorescence elongate, raceme-like or spike-like; phyllaries less than 5 mm and united into a cup.
30. Staminate and pistillate heads separate, the former on elongate branches, the latter at the bases of these branches (rare plants unisexual); larger leaves lobed except on depauperate plants.
30. Staminate and pistillate flowers in the same heads (pistillate at the margin); leaves simple (but coarsely toothed).
31. Heads mostly short-pedicellate, bractless.
31. Heads sessile in the axils of leafy bracts that exceed them.
26. Heads with small to conspicuous ray flowers.
32. Phyllaries (not to be confused with adjacent broad receptacular bracts) in a single series, ± lance-ovate and green, only slightly overlapping at base; branches of inflorescence and at least margins of phyllaries with septate hairs and/or stalked glands; leaves (except sometimes the uppermost) opposite, large (ca. 1–2 dm or even broader), and lobed.
33. Pedicels and phyllaries with stalked glands, without septate hairs; leaves (at least the lower) palmately lobed; rays yellow, ca. 1.3–2 cm long.
33. Pedicels and phyllaries with septate hairs (sometimes with stalked glands as well); leaves deeply pinnately lobed; rays white or pale yellow, minute or to ca. 1 cm long.
Polymnia (in part)
32. Phyllaries various, usually in more than 1 series, or if in 1 series, the pubescence neither septate nor with staked glands (except in Madia); leaves alternate, basal, or opposite (if the latter, less than 1 dm broad).
34. Rays white to pink or rose-purple.
35. Heads solitary (one per stem or at end of a branch); rays showy, conspicuously longer than the involucre.
36. Plants small (less than 2 dm tall), scapose; rays ca. 1 cm or shorter.
36. Plants tall (well over 2 dm), leafy-stemmed; rays ca. 3–6 cm long.
35. Heads several per stem or branch; rays inconspicuous, shorter than the involucre (but may protrude beyond it).
37. Leaves alternate.
37. Leaves opposite.
38. Phyllaries ca. 10–12; leaves lanceolate or lance-elliptic, with obscure petiole if any; pappus none or an obscure crown; receptacular bracts hair-like.
38. Phyllaries ca. 5; leaves with ovate blade and definite petiole; pappus of narrow, flat, fringed scales; receptacular bracts flat, narrow scales.
34. Rays yellow to orange, sometimes mostly red-purple with yellow bands or tips.
39. Disk flowers sterile, the ovary smaller than on fertile ray flowers, and the style undivided; achenes flattened parallel to the phyllaries, wing-margined.
39. Disk flowers fertile, the ovary at least as large as on any fertile ray flowers, and the mature style forked; achenes thick and angled or ± flattened at right angles to the phyllaries, wingless (except in Verbesina).
40. Leaves in a basal rosette; flowers solitary.
40. Leaves (at least some) cauline; flowers normally more than one per stem.
41. Leaves opposite, at least toward base of plant (fragmentary specimens lacking lower part of the stem may be inadequate for identification).
42. Leaves less than 4 mm wide; rays less than 3 mm long and fewer than 4; phyllaries 4 or fewer.
42. Leaves wider; rays longer and more numerous; phyllaries more than 4.
43. Ray flowers sterile, without style; achenes ± compressed but not angled; leaves of some plants alternate on upper part of stem; phyllaries in most species acute or acuminate.
Helianthus (in part)
43. Ray flowers fertile, with style; achenes 3–4-angled; leaves all opposite; phyllaries rounded or blunt at apex.
41. Leaves all alternate.
44. Phyllaries sticky or gummy (appearing strongly varnished when dry), the outer ones with prolonged narrow recurved tip; leaves sessile, clasping, toothed, and with shiny glandular dots on both surfaces; receptacle without chaffy bracts (but long pappus bristles evident).
44. Phyllaries not gummy, without recurved tip; leaves various but without above combination; receptacle with or without chaff.
45. Stem (at least upper half) with prominent green wings decurrent from leaf bases the full length of the internode.
46. Rays cuneate, broadest at the 3 (–4)-lobed apex, gland-dotted at least beneath; receptacle without chaff; leaves gland-dotted on both surfaces; achenes angled and ribbed, the pappus of several thin awn-tipped scales.
Helenium (in part)
46. Rays ± oblanceolate, broadest near or shortly beyond the middle, 2-lobed at apex, not gland-dotted; receptacle with distinct chaff; leaves not gland-dotted; achenes strongly flattened, with 2 persistent rigid pappus-awns.
45. Stem not at all winged.
47. Receptacle and disk flat or nearly so.
48. Ray flowers sterile; achenes wingless; chaff of receptacle consisting of elongate flattish bracts easily seen among the disk flowers; plants common (native or introduced), annual or perennial.
Helianthus (in part)
48. Ray flowers pistillate; achenes winged or chaff none; rare waifs, annual.
49. Leaves less than 3 mm wide (very numerous); pappus of 5 translucent scales narrowed to an awn tip.
49. Leaves much broader; pappus of 2 awns or none.
50. Receptacular chaff none; achenes boat-shaped, wingless, without pappus but strongly curved and spiny down the back; leaves tapered to a sessile, ± clasping base, entire or nearly so.
50. Receptacular chaff elongate; achenes (of disk florets) flattened, winged, with 2 pappus awns; leaves (at least middle and lower ones) with definite petioles and coarsely toothed ± lanceolate to triangular blades.
47. Receptacle (and hence disk) conspicuously dome-shaped, conical, or even cylindrical.
51. Rays strongly drooping; achenes ± flattened; receptacle with chaff subtending both ray and disk flowers, with the bracts curved (like a hood) and densely hairy at the apex, concealing the florets in bud; cauline leaves very deeply pinnately lobed or compound, with narrow segments (or leaflets).
51. Rays mostly spreading; achenes plump, angled; receptacle with chaff none or only on the disk, of various nature but not hood-like; cauline leaves variously lobed or usually unlobed (in some species of Rudbeckia with few broad palmate or pinnate lobes, in Gaillardia sometimes pinnately lobed and toothed).
52. Receptacle with irregular bristle-like hairs not subtending individual florets; pappus of several awn-tipped scales; achenes long-hairy, especially near base; rays mostly 3–5-lobed or -toothed at apex.
52. Receptacle with a chaffy scale subtending each disk floret (and partly surrounding the achene); pappus none or a tiny crown; achenes glabrous; rays 2-lobed or -toothed at apex.
KEY TO GENERA OF GROUP C
1. Leaves all or partly opposite or whorled.
2. Plant a vine, with twining, climbing stem; leaves with distinct wingless petiole and cordate blade.
2. Plant a ± erect herb, the stem not twining or climbing; leaves various (but with petioles [winged] and blades cordate only at middle and lower nodes in Arnica).
3. Leaves pinnatifid-pectinate; plant a malodorous annual with large (ca. 0.5–1 mm) glands on the involucre; pappus bristles united in groups at the very base.
3. Leaves unlobed; plants perennial, with glands (if any) tiny on the involucre; pappus bristles not arising from scale-like bases.
4. Rays bright yellow, showy, greatly exceeding the involucre (ca. 14–25 mm long); leaf blades ± cordate or subcordate, the middle and lower on winged petioles.
4. Rays none; leaf blades tapered to petiole or sessile (or even connate around stem).
5. Leaves mostly alternate (occasionally a few opposite or subopposite); achenes with at least 10 ribs and plumose pappus bristles; disk cream.
Brickellia (in part)
5. Leaves all or mostly opposite or whorled (occasionally the uppermost alternate); achenes with 5 ribs or angles and pappus bristles at most barbellate; disk white, purple, blue, or red-purple.
6. Leaves whorled; heads pale pink to reddish or purple (very rarely albino).
6. Leaves opposite (sometimes a few upper ones alternate); heads white or blue.
7. Florets blue or blue-purple, over 30 per head; receptacle ± conical.
7. Florets white, fewer than 25 per head; receptacle flat or somewhat domed.
8. Leaf blades petiolate, ovate, less than twice as long as broad (rarely 2.5 times).
8. Leaf blades sessile, or if petiolate, lanceolate and ca. 2–4 times as long as broad.
1. Leaves all alternate or basal.
9. Ray flowers ± bright yellow or orange (disk flowers also yellow).
10. Phyllaries in a single series (all or essentially all ± equal in length and overlapping at most a little toward the base, but sometimes a few short bracteoles at base of involucre).
11. Cauline leaves all reduced to entire bracts; stems with solitary heads; disk flowers sterile, few, surrounded by ray flowers many times that number.
11. Cauline leaves (at least the middle and lower) with blades, usually ± deeply lobed; stems with more than 1 head; disk flowers fertile (setting fruit), about as many or more than the ray flowers.
12. Upper half of unbranched portion of stem nearly or quite as leafy as the lower half (i.e., leaves ± equally numerous and of similar size and shape, or only gradually reduced upwards); plants without basal rosette of persistent leaves, usually annual.
13. Leaves mostly ± bipinnatifid; involucre ca. 4–5 mm long; weed of disturbed sites.
13. Leaves entire to coarsely toothed; involucre ca. (5–) 7–10 mm long at maturity; wet open habitats.
12. Upper half of unbranched portion of stem less leafy than the lower half (i.e., leaves sparser and distinctly smaller); plants biennial or perennial, often with crowded basal leaves.
Packera (in part)
10. Phyllaries imbricate (of various lengths, overlapping).
14. Heads small, the disk (receptacle) less than 5 mm broad.
15. Leaves narrowly linear-lanceolate, entire, usually punctate with shiny dots, best developed on the middle of the stem; heads all or mostly sessile or subsessile in little clusters of 2 or more, in a ± corymbiform inflorescence.
15. Leaves various but if entire and linear-lanceolate, then not punctate and/or best developed at the base and/or the inflorescence not corymbiform and/or the heads on distinct pedicels.
Solidago (in part)
14. Heads large, the disk (receptacle) ca. 7 mm or more broad.
16. Leaves entire (or very nearly so).
16. Leaves toothed.
17. Teeth of leaves with prolonged spiny tips.
Grindelia ciliata (Group B)
17. Teeth of leaves blunt or rounded.
9. Ray flowers none or white, blue, pink, or purple (disk flowers may be yellow, and marginal ones may also be enlarged and deeply lobed).
18. Rays present and showy, extending beyond the involucre at least as great a distance as the length of the involucre.
19. Heads ca. 4–6 cm broad, solitary at the ends of stems or branches; phyllaries fringed with long septate hairs; plant an annual, very rarely escaped from cultivation, with broad ovate leaves irregularly and deeply toothed.
19. Heads less than 4 cm broad, usually clustered; phyllaries ciliate or not; plants of most species perennial, native or not, with broad to narrow leaves, at least the cauline ones entire or regularly toothed.
20. Pappus of 2–4 (–6) long (ca. 0.5–1.5 mm) and several much shorter bristles; achenes flat and winged.
20. Pappus of numerous silky hairs; achenes not winged.
21. Phyllaries all or almost all ± equal in length.
22. Cauline leaves consisting of modified broad multi-veined petiolar bracts with at most a rudimentary blade, on a thick (often over 5 mm diameter) stem.
Petasites (in part)
22. Cauline leaves not so modified, on a stem not over 5 (–6) mm thick.
23. Pedicels and phyllaries with ± dense stalked glands.
24. Leaf blades only slightly auriculate; phyllaries usually green throughout; achenes sparsely strigose; stems arising singly from an elongate rhizome; Lake Superior region.
Canadanthus (in part)
24. Leaf blades strongly auriculate; phyllaries usually flushed with purple, especially on the acuminate tip; achenes densely strigose; stems arising in clumps from short, thick rhizomes; southern Michigan.
Symphyotrichum novae-angliae (in part)
23. Pedicels and phyllaries eglandular or at most with obscure glands.
25. Phyllaries at least sparsely pubescent on back, with no distinct expanded apex on central stripe; rays usually white to pink (showy on the few-headed E. pulchellus).
Erigeron (in part)
25. Phyllaries glabrous on back, with central narrow green stripe expanded into a ± diamond-shaped green area below the tip; rays bright blue or purple.
Symphyotrichum (in part)
21. Phyllaries of several lengths, the involucre clearly imbricate.
26. Inflorescence compact, elongate, cylindrical; rays fewer than 10.
26. Inflorescence ± open, corymbiform or paniculate; rays often more than 10.
27. Pappus hairs thickened (slenderly clavate) toward apex; rays white, 12–18; achenes glabrous; leaves ± oblanceolate.
27. Pappus hairs not thickened (if obscurely so, achenes pubescent); leaves various (but not oblanceolate if rays white and 12–18).
28. Blades of at least the lower and/or basal leaves with distinct petioles and cordate to broadly rounded or truncate bases.
29. Involucres mostly (6.5–) 7–9 (–10.5) mm long, with outer phyllaries 1–2.2 mm broad; inflorescence corymbiform.
29. Involucres less than 6.5 (–7.5) mm long, with no phyllaries more than 1 mm broad; inflorescence elongate (racemose or paniculate).
Symphyotrichum (in part)
28. Blades of leaves not cordate or if somewhat so, the leaves sessile, not distinctly petioled.
30. Phyllaries with ± dense stalked glands.
31. Leaf blades only slightly auriculate; phyllaries usually green throughout; achenes sparsely strigose; stems arising singly from an elongate rhizome; Lake Superior region.
Canadanthus (in part)
31. Leaf blades strongly auriculate; phyllaries usually flushed with purple, especially on the acuminate tip; achenes densely strigose; stems arising in clusters from short, thick rhizomes; southern Michigan.
Symphyotrichum novae-angliae (in part)
30. Phyllaries without glands.
32. Basal leaves with blades as broad as 8 cm or more, several times as large as the principal cauline leaves, on long winged petioles; tall (to 2 m) escape from cultivation.
32. Basal leaves (if any) much smaller, scarcely if at all larger than the principal cauline leaves (often withered at flowering time), scarcely if at all petioled; most species clearly native.
33. Phyllaries (at least the middle ones) tough and parchment-like, green at most at tip (the midvein not bordered to the base); pappus hairs slightly thickened toward apex; rays few (ca. 3–8); achenes densely silky.
33. Phyllaries herbaceous in texture, with midvein bordered with color; pappus hairs thickened or (usually) not; rays usually more numerous (if rays few and/or pappus hairs thickened, leaf venation distinctly areolate); achenes glabrous to moderately pubescent.
34. Middle phyllaries with the green zone ± abruptly expanded at or above the middle into a distinct short or elongate broad diamond-shaped area, the lower portion of the phyllaries mostly whitish with a very narrow darker midvein; heads numerous in an elongate to broadly triangular paniculate inflorescence (not flat-topped).
Symphyotrichum (in part)
34. Middle phyllaries with broad dark (green or reddish) zone bordering midvein mostly ± uniform in width (at mid-length, nearly or quite as wide as the pale area on each side); heads 1–7 or numerous in a flat-topped inflorescence.
35. Leaves elliptic, mostly (7–) 10–30 mm wide, glabrous or pubescent but eglandular and reticulate with strongly contrasting dark veinlets and tiny pale areoles ca. 0.6 mm or less across, with flat margins; heads ca. 2 cm or less across, numerous in flat-topped corymbs, with white rays.
35. Leaves linear to very narrowly elliptic (less than 7 mm wide), glandular beneath but not strongly reticulate-veined, with revolute margins; heads ca. 2.5–4 cm across, solitary to few on long pedicels, with pink rays.
18. Rays none or very inconspicuous (extending beyond the involucre, if at all, less than its length), (do not be misled by some species where the marginal disk flowers may be much larger than the central ones).
36. Phyllaries (at least the outer ones) spine-tipped (hooked in Arctium) or strongly fringed or lacerate-margined, or the lobes of the leaves spine-tipped, or both conditions (phyllaries and leaves) present; disk corollas usually very deeply lobed.
37. Spine at tip of phyllary hooked; leaves very large and ovate, not spiny.
37. Spine (if any) at tip of phyllary straight; leaves various.
38. Phyllaries lacerate or fringed at the tip (including a terminal spine or not); leaves without spines.
38. Phyllaries with a terminal spine or none (not otherwise fringed except spiny basally in Silybum); leaves with spine-tipped lobes or spiny margins.
39. Principal cauline leaves at least (6–) 8 cm broad, shallowly if at all lobed; plants either with outer phyllaries at least 1 cm broad at base or with stems broadly winged (the wings averaging over 5 mm broad and densely cobwebby-tomentose).
40. Stem with broad cobwebby-tomentose wings; phyllaries less than 3 mm wide; receptacle without bristles among the florets (but deeply pitted); leaves not variegated.
40. Stem not winged; phyllaries expanded at base to over 1 cm wide; receptacle bristly; leaves variegated (at least the main veins bordered with whitish).
39. Principal cauline leaves less than 6 cm broad, or deeply lobed (sinus more than halfway to midrib); stem wings, if any, not cobwebby-tomentose and phyllaries not over 6 mm wide.
41. Pappus bristles simple (at most slightly barbed); internodes of stem continuously or intermittently winged its entire length.
41. Pappus bristles plumose (feathery with very long fine lateral branches); internodes of most species not (or only slightly) winged.
36. Phyllaries and leaves all without spines; disk corolla deeply lobed or not.
42. Middle phyllaries wholly scarious or with prominent pale to brownish scarious tips and/or margins totaling 1/4 or more of the length or width of the phyllary; corollas (except in staminate Antennaria and Rhaponticum, with pilose phyllaries) thread-like (i.e., extremely slender, ca. 0.1–0.3 mm broad).
43. Mature leaves glabrous or nearly so, glandular-punctate; pappus bristles (the longest) short-plumose; tip of phyllaries pilose with dense straight hairs.
43. Mature leaves lightly to densely tomentose on one or both surfaces, not punctate; pappus bristles at most minutely barbed; tip of phyllaries glabrous or tomentose.
44. Plants mostly stoloniferous with leafy rosettes; cauline leaves much reduced, ± remote; pappus bristles (at least in pistillate or bisexual flowers) united in a ring at the base.
45. Phyllaries white (or pinkish) at least apically; heads unisexual (plants dioecious); inflorescence ± corymbiform.
45. Phyllaries brownish (or purplish) throughout; heads with bisexual flowers centrally, pistillate ones outwards; inflorescence elongate, spicate.
44. Plants annual or rhizomatous, with neither stolons nor basal rosettes; cauline leaves numerous, much overlapping; pappus bristles often separate.
46. Phyllaries tomentose nearly or quite to the tip; receptacle chaffy except at the middle (the chaff grading into the sparse phyllaries, but glabrate).
46. Phyllaries glabrous on at least the apical half; receptacle without chaff.
47. Phyllaries (except at base) pure pearly white, appearing distinctly longitudinally striate (from tiny creases); leaves smooth and glabrous above or with loose white tomentum (rarely with a few tiny gland-tipped hairs hidden in the tomentum); plant rhizomatous and (fresh or dry) without sweetish odor.
47. Phyllaries off-white to brownish, not appearing striate from tiny creases; leaves at least in common species with short-gland-tipped hairs or at least roughened above; plants tap-rooted (rhizome only in Omalotheca sylvatica) and the common species (fresh or dry) with sweetish (brown sugar?) odor especially when crushed.
48. Inflorescence elongate (spicate or racemose); pappus bristles united in a ring at the base; plants rhizomatous.
48. Inflorescence corymbiform (or heads crowded at ends of branches, or sometimes spicate in G. uliginosum with involucres only 2–3 mm long); pappus bristles separate; plants tap-rooted.
49. Involucre ca. 2–2.7 (–3) mm long; plants (except the most depauperate) bushy-branched; heads in clusters overtopped by subtending leaves.
49. Involucre 4.5–6.5 (–7) mm long; plants rarely branched (except at the top or in the inflorescence); heads not overtopped by subtending leaves.
42. Middle phyllaries with scarious margin none or very narrow (1/6 the length of phyllary or less, rarely approaching 1/4 in Liatris); corollas in most species more than 0.3 mm broad.
50. Flowers (except for an occasional albino) purple or pink.
51. Rays present, tiny.
52. Involucre up to 4 mm long.
Conyza (in part)
52. Involucre at least 5 mm long.
53. Pedicels and often phyllaries glandular.
Erigeron acris (in part)
53. Pedicels and phyllaries eglandular.
51. Rays none.
54. Corollas less than 0.2 mm broad, barely toothed at apex; phyllaries with septate hairs, at least on margins.
54. Corollas broader, deeply lobed (sinuses ca. 1 mm or deeper); phyllaries usually glabrous (or minutely ciliate) but in most species glandular punctate.
55. Phyllaries in a single series, of ± equal length (tiny bracteoles may be at base), smooth; cauline leaves reduced to broad bracts (at most a tiny blade at apex); basal leaves ca. 1–3 dm broad.
55. Phyllaries imbricate, ± glandular-punctate; cauline leaves normal; basal leaves much less than 1 dm broad.
56. Pappus usually white, often becoming pink or dingy, of uniform long, plumose or strongly barbed bristles; inflorescence usually ± elongate or spicate.
56. Pappus dark purple or brown, of 2 series: one of long, hair-like, nearly smooth bristles and the other (outer) of short, somewhat flattened bristles; inflorescence ± open and corymbiform.
50. Flowers white, cream, or yellow.
57. Phyllaries in 2 or more series of ± equal length or imbricate.
58. Pappus bristles plumose; leaves, involucre, and achenes all pubescent.
Brickellia (in part)
58. Pappus bristles simple; leaves and involucre glabrous or pubescent (see below); achenes glabrous (usually) or pubescent.
59. Involucre 2.7–4 mm long.
60. Pubescence mostly of spreading, longer hairs; pappus of a single series.
Conyza (in part)
60. Pubescence mostly of appressed antrorse hairs 0.5 mm or shorter; pappus double, with an outer series of minute scale-like bristles.
59. Involucre at least 5 mm long.
61. Pedicels and often phyllaries with minute gland-tipped hairs; leaves lanceolate to oblanceolate; achenes glabrous.
Erigeron acris (in part)
61. Pedicels and phyllaries eglandular; leaves narrowly linear (less than 4 mm wide); achenes pubescent.
57. Phyllaries in a single series of ± equal length, in some species with bracteoles very much shorter and usually narrower at base of involucre.
62. Flowers yellow; cauline leaves deeply pinnatifid, at least toward the base.
63. Upper half of unbranched portion of stem less leafy than the lower half (i.e., leaves sparser and distinctly smaller); biennial or perennial, often with crowded basal leaves.
Packera (in part)
63. Upper half of unbranched portion of stem nearly or quite as leafy as the lower half (i.e., leaves ± equally numerous and of similar size and shape, or only gradually reduced upwards); annual, without basal rosette of persistent leaves.
Senecio (in part)
62. Flowers white to cream; cauline leaves at most toothed.
64. Cauline leaves reduced to broad petiolar (parallel-veined) bracts with at most a rudimentary blade at the apex.
Petasites (in part)
64. Cauline leaves with well developed blades [if plant does not fit well here, try couplet 43].
65. Leaves cauline (remote and few) and basal, long-petioled, coarsely and broadly toothed, shallowly lobed, or entire, with several main palmate or longitudinal veins; pappus bristles scabrous or minutely antrorse-barbed; perennial.
65. Leaves all cauline (crowded and overlapping), sharply toothed, pinnately veined with 1 midrib; pappus bristles smooth; annual.