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Key to Asteraceae, Key A: woody composites (shrubs and lianas)

Asteraceae

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1 Leaves opposite, at least on the lower stem nodes (the leaves higher on the stem sometimes alternate); [tribe Heliantheae or tribe Eupatorieae].
  2 Heads radiate, the rays yellow to orange; disc flowers yellow to orange.
    3 Leaves linear; receptacle epaleate, but densely setose; [extreme s. TX]
      4 Leaves mostly entire, rarely distally 3-lobed, often somewhat glaucous; disc florets 30-100+; receptacle densely setose; pappus of scales
      4 Leaves usually shallowly to deeply 3-9-lobed, green; Disc florets 100+; receptacle with oblong-rectangular paleae; leaves linear or linear-lobed; pappus absent
    3 Leaves lanceolate or broader, 1-5× as long as wide; receptacle paleate; heads borne singly or many; [collectively widespread].
        5 Leaves ovate, rhombic, or pentagonal, unlobed or 3-5-(-7) lobed; leaf blade margins toothed; leaves in part alternate upwards; [of disturbed, suburban areas of FL peninsula]; [tribe Heliantheae; subtribe Helianthinae]
          6 Ray laminae 5-16 mm long; leaf blades 7-33 cm long, the larger deeply 3-7-lobed; petiole bases dilated at base, fused to form a disc of leaf tissue at the stem
        5 Leaves lanceolate to oblanceolate, unlobed or obscurely 3-lobed; leaf blade margins toothed or entire; leaves strictly opposite; [tribe Heliantheae; subtribe Ecliptinae].
             7 Leaves obovate to oblanceolate, unlobed, entire; heads (5-) 8-13 (-18+) mm in diameter; cypselas 3-4-smgled, not winged; [of tidally inundated salt and brackish marshes of the outer Coastal Plain, MD to s. FL, west to s. TX]
             7 Leaves lanceolate, sometimes 3-lobed, usually serrate but sometimes nearly entire; heads 4-8 mm in diameter; cypselas flattened and winged; [TX only]
  2 Heads discoid or disciform (ray flowers lacking); disc flowers pink, purple, whitish, yellow, or orange.
               8 Disc flowers pink, purple, or white.
                 9 Heads small (involucres 2-8 mm high), solitary, axillary in the axils of leaves or leafy bracts (similar to the leaves but smaller) or interpretable as arrayed in bracteate racemes; heads nodding, the involucre 2-7 mm high; [collectively widespread in coastal portions of our area, of maritime situations]; [tribe Heliantheae; subtribe Ambrosiinae]
 Iva
                 9 Heads small to larger (involucres 3-15+ mm high), many, terminal on the branches of corymbiform or paniculiform arrays; heads erect, the involucre 4-12 mm high; [of Coastal Plain of FL, s. GA, and TX].
                   10 Pappus of 4-10 scales, 0.3-7 mm long; [tribe Heliantheae; subtribe Chaenactidinae]
                   10 Pappus of 5-70 barbellate bristles, 3-12 mm long; [tribe Eupatoriae]
                     11 Leaf blades spatulate to obovate, cuneate to attenuate at the base, rounded or shallowly notched at the apex; leaf margins entire; leaves opposite below, alternate higher on the stems; [native of FL]
                       12 Phyllaries broad, 2-3× as long as wide, the inner phyllaries translucent-scarious white to pinkish at their broadly rounded apices, falling as the head goes to fruit
                       12 Phyllaries narrow, 4-7× as long as wide, the inner phyllaries green at their acute to acuminate apices, persistent on the head in age.
                          13 Involucres 2-3 mm in diameter; phyllaries 7-16 in 1-2 series; disc flowers 3-13 per head; [s. FL only (in our region)]
                          13 Involucres 3-7 mm in diameter; phyllaries 25-35 in 2-3 series; disc flowers 10-60 per head; [TX only (in our region)].
                            14 Disc flowers blue to lavender (rarely white); [extreme s. TX]
1 Leaves strictly alternate.
                              15 Heads radiate (with ray and disc flowers) or pseudoradiate (with pseudoradiate flowers only.
                                  17 Rays pink or rose, 30-50 (-70); sprawling viny shrub to 40 dm tall; leaves ovate, averaging ca. 3× as long as wide, with clasping base, with a midvein and lateral veins and tertiary reticulation
                                  17 Rays white, 5-34+; shrubs 2-30 dm tall; leaves either obovate to oblanceolate, averaging ca. 4× as long as wide, dentate, or linear, ca. 10× as long as wide, entire, cuneate.
                                    18 Rays white, 5-11 (-15); leaves linear, ca. 10× as long as wide, entire; [native, s. and se. TX]
                                    18 Rays white, 21-34+; leaves obovate to oblanceolate, averaging ca. 4× as long as wide, dentate; [non-native, known in our region only from NY]
                                16 Rays or pseudorays yellow, orange-yellow, or light creamy yellow.
                                       19 Heads pseudoradiate, with 11-25 pseudoray flowers and 0 disc flowers; leaves 8-70 mm wide
                                       19 Heads radiate, with (0-) 1-11 (-15) ray flowers and 1-15 (-20) disc flowers; leaves (or their segments) 0.5-10 mm wide.
                                         20 Phyllaries in 1-2 series and equal or subequal in length to one another, the phyllaries often coherent/fused (the involucre thus appearing as a cylinder with ribs extending from base to top; calyculus (of bracts subtending the phyllaries and differing from them in texture, color, or orientation) present; [tribe Senecioneae]
                                         20 Phyllaries in 3-17 series and unequal in length (imbricated); calyculus absent.
                                             22 Pappus of 40-60 barbellate bristles; ray blades 4-6 mm long; leaf surfaces minutely pebbled; intricately branched shrubs to 1 m tall, with persistent sterile shoots with evergreen leaves and annual flowering shoots (the entire shoot and leaves deciduous); [Coastal Plain, se. NC south to Panhandle FL and s. MS]
                                             22 Pappus absent, a low coroniform structure, or of scales; ray blades 2-3.5 mm long; leaf surfaces planar/revolute; shrubs 1-15 dm tall, not differentiated into evergreen, sterile shoots bearing deciduous, fertile shoots; [OK and TX westwards, very rarely as a waif eastwards].
                                                        27 Leaves strongly basally disposed, crowded in the lowermost, woody or semiwoody portion of the stem
                                                              30 Leaf blades obovate, spatulate, or orbiculate, rounded or slightly notched at the apex; leaf blade surfaces gray-green on both surfaces, granular when young; disc flowers 5 per head; [FL]
                                                              30 Leaf blades elliptic, acute to acuminate at the apex; leaf blade strongly bicolored above and below, the upper surface dark green and glabrate, the lower surface densely and finely tomentose and strongly whitened, the upper surface dark green and glabrate or glabrous; disc flowers 4-25 per head; [s. TX]

Key to Asteraceae, Key B: herbaceous composites with opposite or whorled leaves
and discoid or disciform heads (lacking ray florets)

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1 Pappus present, of 5-60 barbellate bristles; receptacle naked (without paleae or well-developed bristles); [tribe Heliantheae; subtribe Eupatoriae].
  2 Plant a twining herb, phyllaries and disk florets 4 per head
  2 Plant stiffly erect to sprawling but never twining, phyllaries and disk florets usually > 4 per head.
    3 Leaves in whorls of 3-7, > 2 cm wide
    3 Leaves opposite, rarely alternate or whorled, if whorled, < 2 cm wide.
      4 Cypselae rostrate (with long beaks); the achene portion not bearing ribs
      4 Cypselae not beaked, the achene variously ribbed.
        5 Achenes (and ovaries) (3-) 4-5-ribbed; outer phyllaries not noticeably longitudinally striate.
          6 Heads pink to blue.
             7 Phyllaries in 2-4 series, persistent (or deciduous in Praxelis).
               8 Heads pink (rarely bluish); receptacles flat; florets 18-25 per head; leaves sometimes gland-dotted
               8 Heads blue; receptacles conic; florets 25-70 per head; leaves gland-dotted.
                 9 Bristles ca. 40; florets 25-30; phyllaries 15-25, unequal, deciduous (absence apparent in fruit)
          6 Heads white to cream or, rarely, pale lilac.
                     11 Phyllaries not strongly imbricate, with the principal ones subequal and sub-biseriate; petioles 0.5-10 cm
1 Pappus either absent, or of scales, setae, or awns; receptacle naked, paleate, or bearing bristles.
                       12 Leaves whorled, linear, < 2 mm wide; head solitary; [aquatic herb growing in shallow stagnant water]
                       12 Leaves opposite (or alternate in part), broader in shape and > 5 mm wide; heads typically not solitary; [terrestrial or wetland plants].
                            14 Pappus of 2-12 scales; heads white, pink, or blue (yellow in Schkuhria).
                              15 Heads with 20-125 florets; leaves serrate or ± dentate (at least distally); [rarely naturalized exotics or s. TX/FL natives]; [tribe Eupatorieae].
                                16 Leaves petiolate; corolla tube glabrous, typically blue or lavender colored (sometimes white tinged); heads with 20-125 florets; [naturalized exotics or s. FL native]
                                16 Leaves sessile; corolla tube glandular-pubescent, typically white colored (sometimes pink-purple tinged); heads with 75-125 florets; [s. TX native]
                              15 Heads with 10-30 florets (or fewer in Schkuhria); leaves entire; [natives, of FL, s. GA, MS, and TX in our area]; [tribe Heliantheae; subtribe Chaenactidinae].
                                  17 Leaves 3-5 lobed (or foliolate); cypselae with curled hairs (Florestina tripteris) or villous on angles (Schkuhria pinnata); [s. TX in our area or ne. waif].
                                    18 Heads discoid, sometimes with 1 (-2) diminuitive rays, corolla (of discs) yellow; cypselae villous, at least at bases or on angles; [waif of ne US, native in sw. US]
                                  17 Leaves simple or unlobed; cypselae with straight hairs; [variously distributed in s. GA and FL w. to MO and s. TX]
                            14 Pappus none, or of a few bristles or irregular coroniform lobes; heads green to yellow.
                                       19 Heads bright yellow, closely aggregated into corymbiform arrays of flat-topped to dome-shaped glomerules
                          13 Receptacles with paleae or well-developed bristles (the pales sometimes modified into specialized perigynia or burs surrounding the achene).
                                           21 Involucre of four decussate, deltoid bracts (the outer two large and longer than and often enclosing the flowering heads); pappus absent; paleae tightly enclosing the cypselae; plants rooting at the nodes, sometimes free-floating in water; [uncommon non-native, c. FL]
                                           21 Involucre not of four decussate, deltoid bracts; plants not with the above combination of characters; [widespread natives and non-natives]
                                             22 Heads small, less than 1 cm in diameter at anthesis (the female heads enlarging in Xanthium); disc florets dull white or suffused with green or purple; florets mainly unisexual (either in the same heads and then males central and females peripheral, or in separate female and male heads); female florets 0-8 per head; [tribe Heliantheae; subtribe Ambrosiinae].
                                               23 Heads unisexual; cypselas shed within an indurated bur or “nut” with hooked or straight spines developed from the phyllaries and/or paleae.
                                               23 Heads bisexual, with functionally male and female flowers in the same head; cypselas shed individually, not enclosed.
                                             22 Heads larger, mostly > 1 cm in diameter at anthesis; disc florets conspicuously white, yellow, pale yellow, or purple; florets mainly bisexual; female florets > 12 per head (except 2-8 in Polymnia and 8-15 in Verbesina occidentalis).
                                                      26 Leaves strongly basally disposed, the basal-most leaves sitting almost flat on the ground and overlapping; disc flowers maroon-purple
                                                      26 Leaves mainly or strictly cauline (not basally disposed); disc flowers white, yellow, or reddish-brown.
                                                          28 Involucre of phyllaries not subtended by a calyculus (phyllaries sometimes in 2+ series, but without obvious calyculi below).
                                                              30 Plants primarily prostrate or trailing, sometimes erect; heads with or without ray florets; [habitats various, widespread natives and non-natives]

Key to Asteraceae, Key C: herbaceous composites with opposite leaves and radiate heads

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1 Ray florets white, pink, or purple (rarely pale yellow or lavender).
  2 Ray floret (the lamina) persistent on the achene and becoming papery and bleached
  2 Ray floret (the lamina) articulate from the achene and falling, thus the mature heads not appearing papery.
    3 Pappus of a minute crown (coroniform); disc florets white or whitish.
    3 Pappus not only coroniform, either absent or variously composed of scales, awns, or plumose bristles (Galinsogeopsis has 2 antrorsely barbed bristles plus a crowns of laciniate scales); disk florets yellow, red-brown, or pinkish.
      4 Heads with an involucre not subtended by a calyculus.
        5 Rays pink, the laminae 5-14 mm long; [OK and TX westward; subtribe Cheaenactidinae]
        5 Rays white or whitish-yellow; the laminae shorter, typically < 5 mm long (occasionally longer in Polymnia).
          6 Plants larger, 50-150+ cm tall; perennials; leaves > 10 cm long, sometimes with winged petioles or clasping basal appendages; disc florets functionally staminate; [natives of higher-quality, limestone or novaculite habitats; subtribe Polymniinae]
          6 Plants smaller, 2-40 cm tall or long (if stems > 40 cm then plants usually procumbent or decumbent); annuals or perennials; leaves usually < 10 cm long, lacking winged petioles or clasping basal appendages; disc florets bisexual and fertile.
             7 Stems usually copiously glandular-pubescent; leaf blades cordate to subdeltate or usually strongly 3-lobed (but not pinnate), the margins singly or doubly crenate; disc florets 40-100+; plants erect to decumbent; [native, s. TX westward; subtribe Peritylinae]
             7 Stems not copiously glandular-pubescent; leaf blades lanceolate to broadly ovate or deltate, or pinnately to palmately lobed (Tridax); plants erect or ascending to procumbent (Tridax]; [non-natives of disturbed habitats, widespread; subtribe Galinsoginae].
               8 Plants with leaves simple, unlobed; pappus either absent or of 5-20 laciniate or fimbriate scales; plants annual, erect
               8 Plants usually with a mix of simple and 3-lobed leaves; pappus usually of ca. 20 plumose (or setiform) scales; plants perennial, usually at least somewhat procumbent
      4 Heads with an involucre subtended by a calyculus of bracts (these often but not always reflexed); the phyllaries often appearing somewhat translucent or of a distinctly different color, shape, or texture from the leafy colored bracts below; [tribe Heliantheae; subtribe Coreopsidinae].
                 9 Phyllaries connate for at least ¼ their length; heads with or without ray florets; [MS westwards in our area]
                 9 Phyllaries distinct; heads with ray florets; [collectively widespread in our area].
                   10 Cypselas beaked, not strongly flattened, 7-30 mm long, with 1 groove per face; leaves highly dissected
                   10 Cypselas beakless, more or less strongly flattened and also often winged, 1.2-16 mm long, with 0 or 2 grooves per face; leaves simple to highly dissected.
                     11 Cypselas 2.5-16 mm long, usually not winged; pappus awns (if present) usually retrorsely barbed; rays white
                     11 Cypselas 1.2-4 mm long, winged (C. nudata) or not (C. rosea); pappus awns (if present) barbless; rays pink, purple, or white
1 Rays predominantly yellow, orange, or red (sometimes with some brown, maroon, or purple coloration as well).
                          13 Leaves and phyllaries with large, scattered, embedded oil glands, making the plants strongly aromatic (the glands translucent in living plants, usually golden-brown or blackish in herbarium specimens); plants annual, decumbent and much branched from the base (except Tagetes, annual and generally erect and sparingly branched); [tribe Heliantheae; subtribe Pectidinae].
                            14 Leaves pinnately lobed or pinnatisect (pinnately divided nearly to the midrib but the leaflets not separate), the margins of terminal segments usually serrate (sometimes entire).
                                  17 Phyllaries distinct to their bases, or nearly so; ray florets 5-8; heads borne singly or in pairs/triplets; leaf surfaces puberulent
                          13 Leaves and phyllaries lacking embedded oil glands, though smaller punctate glands sometimes present; perennial or annual plants, upright and little or moderately branched below the inflorescence.
                                       19 Leaves mainly basal or basally disposed (a few pairs low on the stem), the blades elliptic to ovate, the surfaces hirsute and stipate-glandular
                                         20 Pappus absent, of scales, or coroniform (if coroniform then with 6-8 barbellulate bristles as in Jamesianthus); leaf blades unlobed; collectively widespread, including c. TX]
                                           21 Heads smaller and many (10-300+), arranged into dense, flat-topped corymbs; disc florets 1-15; ray florets 0-2, the laminae inconspicuous; phyllaries 6 (-9), in 1 series; [collectively more widespread but absent from n. AL and wc. GA]
                                           21 Heads larger and fewer (< 9 per inflorescence), arranged singly or in loose corymbs; ray florets 6-14, the laminae conspicuous; phyllaries 12-18, broadly ovate, squarrose and in several imbricate series; [on calcareous substrates in n. AL and wc. GA]
                                             22 Disc florets functionally staminate (“sterile”, not producing cypselae), the style undivided, their ovaries much smaller than ovaries of the ray florets (which are functionally pistillate).
                                               23 Inner phyllaries unarmed, not becoming bur-like (though those of Melampodium do invest the fruit).
                                                 24 Plants with tack-glands or pit-glands on stems, leaves, and/or phyllaries; [waif, e. TX; native further westward]
                                                        27 Plants perennial, often trailing; pappus persistent, forming a minute, half-cup-shaped crown; [e. LA eastward, e. of MS river]
                                                      26 Taller, robust plants, the stems usually 5-40 cm long at maturity, erect; pappus absent or of 2 awns.
                                             22 Disc florets functionally bisexual (“fertile”, producing cypselae), the style divided, their ovaries as large as, or larger than, ovaries of the ray florets (which may be either functionally pistillate or completely neuter).
                                                                       34 Paleae not notably clasping the cypsela; cypselae notably flattened (or weakly compressed/angled in Guizotia); heads small, the receptacle 3-8 mm in diameter (ca. 10-15 mm in Guizotia).
                                                                           36 Cypselae of the rays and discs similar, monomorphic and not as above (the achenes weakly dimorphic in C. vialis, but the apical awns of similar length and the margins with only small, inconspicuous winglike projections)
                                                                       34 Paleae either entirely enveloping and falling with each cypsela or conduplicate (V-shaped in cross section), the 2 sides of the V partially clasping the cypsela; cypselae flattened, terete, or angled; heads mostly larger.
                                                                              37 Phyllaries apparently 4, the outer 4 foliaceous and forming a fused quadrangle which conceals the much smaller and narrower inner phyllaries (each inner phyllary subtending a ray floret); cypselae finely 32-40 ribbed
                                                                              37 Phyllaries not as above, instead 5 or more and not forming a conspicuously fused quandrangle; cypselae angled or smooth (sometimes angled, but lacking many fine ribs)
                                                                                  39 Disc florets without hairy staminal filaments; pappus absent or of 2-3 scales or awns (sometimes accompanied by up to 8-12 additional shorter scales in Helianthus and Simsia, but these readily falling); [collectively widespread].
                                                                                                 46 Leaf blades usually broader (if linear, leaves either whorled or pappus present); plants annual or perennial, with or without woody caudices; pappus typically of scales or awns; [collectively widespread in our flora area].
                                                                                                   47 Leaves linear, lanceolate, or ovate, almost always some leaves on a plant > 7 mm wide; plants from crowns, some species with thickened vertical storage roots (only H. tuberosus producing horizontal tubers); [collectively widespread in our area]