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Key to Tithonia

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1 Plant a perennial or somewhat shrubby; phyllaries 16-28; ray laminae 48-69 mm long
1 Plant an annual; phyllaries 12-16; ray laminae 20-33 mm long

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 absent, of 1-many scales, or of retrorsely barbed awns (or plumose bristles in Tridax procumbens); 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]
        5 Rays white or whitish-yellow; the laminae typically < 5 mm long (occasionally longer in Polymnia); [collectively widespread]
          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]
          6 Plants smaller, 2-40 cm tall or long (if stems > 40 cm then plants usually procumbent); annuals or perennials; leaves usually < 10 cm long, lacking winged petioles or clasping basal appendages; disc florets bisexual and fertile; [non-natives of disturbed habitats].
             7 Plants with leaves simple, unlobed; pappus either absent or of fimbriate to aristate scales; plants annual, erect
             7 Plants usually with a mix of simple and 3-lobed leaves; pappus plumose; 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].
               8 Phyllaries connate for at least ¼ their length; heads with or without ray florets; [MS westwards in our area]
               8 Phyllaries distinct; heads with ray florets; [collectively widespread in our area].
                 9 Cypselas beaked, not strongly flattened, 7-30 mm long, with 1 groove per face; leaves highly dissected
                 9 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.
                   10 Cypselas 2.5-16 mm long, usually not winged; pappus awns (if present) usually retrorsely barbed; rays white
                   10 Cypselas 1.2-8 mm long, usually winged; pappus awns (if present) barbless or antrorsely barbed; rays pink, purple, or white
1 Rays predominantly yellow, orange, or red (sometimes with some brown, maroon, or purple coloration as well).
                       12 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].
                          13 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).
                              15 Pinnate leaf segments linear, 1-3 mm wide; calyculus present, of linear bracts and subtending the involucre.
                                16 Phyllaries distinct to their bases, or nearly so; ray florets 5-8; heads borne singly or in pairs/triplets; leaf surfaces puberulent
                                16 Phyllaries connate > ½ their length; ray florets 5-21; heads borne singly; leaf surfaces glabrous to variously pubescent/floccose
                       12 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.
                                    18 Leaves mainly basal or basally disposed (a few pairs low on the stem), the blades elliptic to ovate, the surfaces hirsute and stipate-glandular
                                    18 Leaves mainly cauline, the blades primarily linear, lanceolate oblanceolate, or occasionally oblong (if ovate, then leaves mostly cauline), the surfaces glabrous to strigose but not stipitate-glandular
                                       19 Pappus absent or of 1-2 antrorsely-barbed or subplumose bristles; leaf blades usually lobed; [c. TX westward]
                                       19 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]
                                         20 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]
                                         20 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]
image of plant
Show caption*© Scott Ward
                                           21 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).
image of plant
Show caption*© Swarochi Tathagath, some rights reserved (CC BY), uploaded by Swarochi Tathagath
                                             22 Inner phyllaries prickly with straight or uncinate prickles, and each enveloping a cypsela and swelling into a bur-like structure
                                             22 Inner phyllaries unarmed, not becoming bur-like (though those of Melampodium do invest the fruit).
                                               23 Plants with tack-glands or pit-glands on stems, leaves, and/or phyllaries; [waif, e. TX; native further westward]
                                                      26 Plants perennial, often trailing; pappus persistent, forming a minute, half-cup-shaped crown; [e. LA eastward, e. of MS river]
                                                      26 Plants annual, erect; pappus absent (cypselae with 2 pappus-like processes originating from cypsela wings); [w. LA westward, w. of MS river]
image of plant
Show caption*© Alan M. Cressler
                                                    25 Taller, robust plants, the stems usually 5-40 cm long at maturity, erect; pappus absent or of 2 awns.
                                           21 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).
                                                                   32 Plants with tack-glands or pit-glands on stems, leaves, and/or phyllaries; [waif, VA and NC northward; subtribe Madiinae]
                                                                   32 Plants without tack-glands or pit-glands on stems, leaves, and/or phyllaries; [natives and non-natives, collectively widespread]
                                                                     33 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).
                                                                     33 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.
                                                                           36 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
                                                                           36 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)
                                                                                38 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 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]
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