Dahlia, Cavanilles, 1791

Reyes-Santiago, Jerónimo, Islas-Luna, María De Los Ángeles, Munguía-Lino, Guadalupe & Castro-Castro, Arturo, 2019, Dahlia mixtecana (Asteraceae, Coreopsideae), a striking new species from Oaxaca, Mexico, Phytotaxa 394 (3), pp. 209-218 : 215-216

Key to the sections and species of Dahlia inhabit in Oaxaca and species in Dahlia sect. Entemophyllon related to D. mixtecana

1. Plants liana-like, producing aerial roots [ Dahlia sect. Epiphytum Sherff (1951: 21) ] ............................................... D. macdougallii

- Plants growing erect, roots tuberous and anchored in the soil...........................................................................................................2

2. Large suffruticose plant 2–9 m tall; most or all shoots sprouting from ligneous stems of former seasons; stems (1.5–) 3–10 cm wide, pinnules opposite on the rachilla [ Dahlia sect. Pseudodendron Sherff (1951: 69) ]..........................................................................3

- Plant herbaceous 0.4–3 m tall or suffruticose 0.9–1.5 m tall; sprouting from rootstock and thick tuberous roots; stems 0.3–2 cm wide; pinnules opposite or alternate on the rachilla...........................................................................................................................5

3. Median leaves, or at least most of them, once pinnate................................................................................................. D. tenuicaulis

- Median leaves bipinnate.....................................................................................................................................................................4

4. Stems not furrowed; leaves dark green, their base not enlarged and claspering............................................................ D. imperialis

- Stems distinctly furrowed; leaves light fresh green with an enlarged, claspering base ............................................. D. campanulata

5. Leaves bipinnatisect to bipinnate-pinnatisect; petiole solid or hollow; pinnules or pinnular segments invariably alternate on the rachilla ( Dahlia sect. Entemophyllon )................................................................................................................................................6

- Leaves pinnate to pinnatisect; petiole solid; pinnules or pinnular segments opposite on the rachilla or if alternate then the petiole hollow ( Dahlia sect. Dahlia )............................................................................................................................................................13

6. Plant with a solitary shoot .......................................................................................................................................... D. congestifolia

- Plant with several shoots....................................................................................................................................................................7

7. Plant herbaceous or sub-herbaceous...................................................................................................................................................8

- Plant suffruticose..............................................................................................................................................................................11

8. Ray florets yellow........................................................................................................................................................... D. mixtecana

- Ray florets lilac...................................................................................................................................................................................9

9. Leaves dull dark green; the ultimate segments of the pinnules up to 2 mm wide..................................................... D. foeniculifolia

- Leaves fresh green; the ultimate segments of the pinnules up to 9 mm wide..................................................................................10

10. Herbaceous plants; heads 3.5–6 cm diameter across the extended ray florets................................................................... D. dissecta

- Subherbaceous plants; heads 5.5–8.5 cm diameter across the extended ray florets...................................................... D. sublignosa

11. The ultimate segments of the pinnules 5–16 mm wide ............................................................................................. D. scapigeroides

- The ultimate segments of the pinnules 0.5–5.5 mm wide................................................................................................................12

12. Leaves 20–35 cm long; outer involucral bracts 10–14 mm long, 4–7 mm wide; heads 5–6.5 cm in diam. (across the extended rays) .................................................................................................................................................................................. D. rupicola

- Leaves 12–18 cm long; outer involucral bracts 5–9 mm long, 2–3.5 mm wide; heads 3–4.2 cm in diam. (across the rays).............. ............................................................................................................................................................................................. D. linearis

13. Rays yellow, orange, orange-red, scarlet, bright red, dark red or blackish red................................................................................14

- Rays whitish-purple, purple or violet-purple, seldom reddish purple or pure whitish.....................................................................16

14. Plants 0.45–3 m tall; leaves 12–35 cm long, simple to tripinnate and alternate or whorled; rays yellow, orange, orange-red, scarlet, bright red, dark red or blackish red ................................................................................................................................... D. coccinea

- Plants 0.25–1.2 m tall; leaves 6–18 cm long, pinnate to bipinnate and alternate; rays yellow........................................................15

15. Plants 0.25–0.6 m tall; conspicuously pubescent stems; pinnate leaves; petioles 0.8–4.5 cm long; 1–4 heads per plant or on each main branch; disc florets 3.5–4.5 mm long ........................................................................................................................... D. tenuis

- Plants 0.9–1.2 m tall; smooth to puberulent stems; bipinnate leaves; petioles (3–) 6.5–7 cm long; 3–6 heads per plant or on each main branch; disc florets 7–10 mm long ........................................................................................................................ D. mixtecana

16. Petiole broadly auriculate-winged at the base, 0.8–1.2 cm wide.....................................................................................................17

- Petioles without wings......................................................................................................................................................................18

17. Stems with distinct furrows; median leaves not markedly scabrous above ................................................................... D. pteropoda

- Stems without distinct furrows; median leaves usually scabrous above........................................................................ D. sorensenii

18. Herbaceous stems; pinnate to bipinnate leaves ................................................................................................................. D. australis

- Woody stems; entire to pinnate leaves.............................................................................................................................................19

19. Entire or rarely pinnate leaves; outer involucral bracts 4–8 mm long; ray florets (1.3–) 2.6–3.2 cm long .................... D. calzadana

- Pinnate leaves; outer involucral bracts 12–17 mm long; ray florets 3.5–5.5 cm long ..................................................... D. apiculata