No key was found for the requested taxon, but its parent (Tagetes) is keyed as shown below.

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

Asteraceae

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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]