Dahlia, Cavanilles, 1791

Reyes-Santiago, Jerónimo, Islas-Luna, María De Los Ángeles, Macías-Flores, Rafael Guadalupe & Castro-Castro, Arturo, 2018, Dahlia tamaulipana (Asteraceae, Coreopsideae), a new species from the Sierra Madre Oriental biogeographic province in Mexico, Phytotaxa 349 (3), pp. 214-224 : 221-222

Key to the species of genus Dahlia of the Sierra Madre Oriental

1. 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) ] ................................................... D. tenuicaulis

- 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 ......................................................................................................................... 2

2. Leaves bipinnatisect to bipinnate-pinnatisect; petiole solid or hollow; pinnules or pinnular segments invariably alternate on the rachilla ( Dahlia sect. Entemophyllon ) .............................................................................................................................................. 3

- Leaves pinnate to pinnatisect; petiole solid; pinnules or pinnular segments opposite on the rachilla or if alternate then the petiole hollow ( Dahlia sect. Dahlia ) ............................................................................................................................................................ 7

3. Plant herbaceous, 0.7–0.9 m tall; outer involucral bracts 1.8–5.5 mm long .................................................................................... 4

- Plant suffruticose, 1.4–2.5 m tall; outer involucral bracts (5.5–) 7–19 mm long .............................................................................. 5

4. Stems from the current year arising from a crown of tuberous rootstock; leaves 10–15 cm long; ultimate segments 2–9 mm wide; outer involucral bracts 1.8–4 mm wide ............................................................................................................................ D. dissecta

- Stems from the current year branching from short ligneous portions of the previous year growth; leaves 11–19 cm long; ultimate segments 0.5–5.5 mm wide; outer involucral bracts 2.5–5.5 mm wide ...................................................................... D. sublignosa

5. Stems living only one season, the current season growth arising from a crown of tuberous rootstock beneath the soil .................... .................................................................................................................................................................................. D. foeniculifolia

- Stems living more than one season and branching to produce the current season growth .............................................................. 6

6. Outher involucral bracts 12–19 × 5–11 mm; ultimate segments of the pinnules 5–22 mm wide ........................... D. scapigeroides

- Outher involucral bracts (5.5–)7–9 × 2–3.5 mm; ultimate segments of the pinnules 1–4.5 (–5.5) mm ........................... D. linearis

7. Ray florets bright yellow, pale yellow, orange, orange-reddish, scarlet, bright red, blackish-red or light violet to almost white ... 8

- Ray florets whitish-purple, violet, purple, or dark blackish-purple ................................................................................................. 9

8. Leaves extremely variable from simple and unlobed to tripinnate, membranaceous, upper leaf surface glabrous or pubescent; ray florets bright yellow, orange, orange-reddish, scarlet, bright red or blackish-red ........................................................... D. coccinea

- Leaves pinnate, leaf velvety and soft, upper leaf surface felted-tomentose; ray florets light violet to almost white or pale yellow .. .............................................................................................................................................................................................. D. mollis

9. Ray florets dark blackish-purple with a red zone towards the base ......................................................................... D. atropurpurea

- Ray florets whitish-purple, purple or violet ................................................................................................................................... 10

10. Principal leaves crowded near the base of the stem, rosette-like; involucral bracts erect or ascending in anthesis ..... D. scapigera

- Principal leaves not crowded near the base of the stem, not rosette-like; involucral bracts reflexed or merely spreading at anthesis ........................................................................................................................................................................................... 11

11. Pinnules or pinnular segments alternate on the rachilla; petiole hollow ........................................................................... D. merckii

- Pinnules or pinnular segments opposite on the rachilla; petiole solid or hollow ............................................................................ 12

12. Heads 12–13.5 cm in diam. across the extended rays.....................................................................................................................13

- Heads 4.5–10 cm in diam. across the extended rays ...................................................................................................................... 14

13. Median leaves 19–24 cm long ......................................................................................................................................... D. neglecta

- Median leaves 27–35 cm long ...................................................................................................................................... D. spectabilis

14. Disc florets yellow or more often yellow below and purple, blackish or reddish-blackish above ................................................. 15

- Disc florets yellow .......................................................................................................................................................................... 16

15. Outer involucral bracts 7–15 × 2.5–6 mm, linear-lanceolate, oblong-spatulate or obovate ............................................ D. australis

- Outer involucral bracts 10–17 × 1.5–4 mm, linear-lanceolate, long-attenuate and flagelliform ....................................... D. moorei

16. Leaflets lanceolate or ovate; solid or hollow petiole; outher involucral bracts 6–8(–13) × 1–3.8 mm .......................................... 17

- Leaflets ovate; solid petiole; outher involucral bracts 10–24 × 1.8–6.5 mm ................................................................................. 18

17. Stems cylindrical and glabrescent, internodes 5–9.5(–12) × 0.3–0.7 cm; stipels present only in the first pair of leaflets; synflorescence with (1–)2–6 heads; the heads 4.5–6 cm wide across the extended rays; cypsela fusiform ............................................ D. tubulata

- Stems hexagonal, villous in the upper portion of the nodes and the base of the petioles, internodes 3–5.5 × 1–1.5 cm; stipels present from the first to the third pair of leaflets; synflorescence with (1–)15–25 heads; the heads 6.5–10 cm wide across the extended rays; cypsela clavate ........................................................................................................................................................... D. tamaulipana

18. Leaflets with cuspidate apex; outher involucral bracts 18–24 × 3.5–6.5 mm, oblanceolate to spatulate ..................... D. cuspidata

- Leaflets with attenuate apex; outher involucral bracts 10–13 × 1.8–2.5 mm, slightly spatulate ................................... D. hjertingii