Exacum, Linnaeus, 1753

Geethakumary, M. P., Deepu, S., Kissling, J. & Pandurangan, A. G., 2022, Revisiting the taxonomy of Exacum courtallense (Gentianaceae) and recognizing E. courtallense var. laxiflorum at the species rank, Phytotaxa 559 (2), pp. 185-192 : 191

Key to Exacum species in the Western Ghats

1. Flowers 4-merous ...............................................................................................................................................................................2

- Flowers 5-merous ...............................................................................................................................................................................8

2. Calyx lobes without wings .................................................................................................................................................................3

- Calyx lobes with prominent wings .....................................................................................................................................................4

3. Flowers subsessile; calyx wings without prominent veins................................................................ E. sessile Linnaeus (1753: 112)

- Flowers pedicellate; calyx wings with prominent veins................................................................... E. lawii C.B. Clarke (1885: 98)

4. Leaves 3-veined (midvein with one secondary vein on each side) ...................................... E. pedunculatum Linnaeus (1753: 112)

- Leaves 5-veined (midvein with two secondary veins on each side) ..................................................................................................5

5. Anthers oblong ...................................................................................................................................................................................6

- Anthers linear .....................................................................................................................................................................................7

6. Leaves with a distinct petiole; calyx wings truncate ...................................................................... E. petiolare Grisebach (1845: 46)

- Leaves sessile; calyx wings cordate .............................................................................................. E. pumilum Grisebach (1845: 46)

7. Calyx lobes cuspidate with broad rounded dorsal wing; anthers curved ................................ E. tetragonum Roxburgh (1832: 398)

- Calyx lobes acuminate with a narrow dorsal wing; anthers straight ............................................ E. grande Klackenberg (1985: 43)

8. Dorsal side of the anther with a papilla present near the apex ...........................................................................................................9

- Dorsal side of the anther without a papilla.......................................................................................................................................14

9. Leaves petiolate or ± sessile.............................................................................................................................................................10

- Leaves amplexicaul or semiamplexicaul..........................................................................................................................................12

10. Perennial herbs; anthers oblong............................................................................ E. idukkianum Geethakumary et al. (2016a: 226)

- Annual herbs; anthers linear.............................................................................................................................................................11

11. Stem 4-angled, winged; fruiting pedicel drooping....................................................................... E. wightianum Arnott (1839: 176)

- Stem 4-lineolate, not winged; fruiting pedicel not drooping.................................................. E. klackenbergii Gopalan (2002: 271)

12. Style shorter than anthers ......................................................................................... E. keralense Geethakumary et al. (2016b: 429)

- Style longer than anther....................................................................................................................................................................13

13. Leaves ovate, papilla in the dorsal side of anther distinct.................................................... E. atropurpureum Beddome (1874: 24)

- Leaves elliptic, papilla in the dorsal side of anther indistinct ............................................ E. anamallayanum Beddome (1874: 33)

14. Succulent herbs with a pincushion habit ..........................................................................................................................................15

- Slightly to much-branched ascending herbs.................................................................................................................. E. laxiflorum

15 Flowers solitary, long-pedicellate.......................................................................................... E. travancoricum Beddome (1874: 24)

- Flowers in multiflorous cymes, short-pedicellate ....................................................................................................... E. courtallense