Key to the species of Meriania in Peru

1. Leaf blades with dentate-undulate, revolute auricles at the base (Fig. 4L), and punctiform abaxial surfaces (Fig. 4B) M. cuzcoana

- Leaf blades without auricles (but M. rigida and M. zunacensis with revolute bases, and M. franciscana and M. neillii with slightly revolute bases), and abaxial surface not punctiform ..........................................................................................................................2

2. Inflorescences solitary, dichasia 3 or 9-flowered (often reduced to 5-flowered) ...............................................................................3

- Inflorescences in panicles with more than 10 flowers (but see comments below M. hirsuta)...........................................................5

3. Calyx calyptrate with irregular dehiscence ................................................................................................................... M. sessilifolia

- Calyx lobed with regular dehiscence..................................................................................................................................................4

4. Terminal branches and leaf blades glabrous; leaf blades 7.7–10 cm long; hypanthium terete; calyx with acute dorsal projections .. .......................................................................................................................................................................................... M. speciosa

- Terminal branches and abaxial leaf blades moderately to densely furfuraceous; leaf blades 2.3–8.2 cm long; hypanthium slightly costate; calyx with acicular dorsal projections (Fig. 5H) .............................................................................................. M. prunifolia

5. Leaf blades bullate (Fig. 4A); corolla campanulate and deep red; stamen connectives with dorsal-basal appendages almost perpendicular to thecae (Fig. 6G).......................................................................................................................................................6

- Leaf blades flat to bullate; corolla spreading or campanulate, white, pink, pink-orange to reddish-orange, or fuchsia to reddish-purple but never deep red (except red in M. rubriflora); stamen connectives with dorsal-basal appendages not perpendicular to thecae..................................................................................................................................................................................................9

6. Nodes with developed interpetiolar flaps...........................................................................................................................................7

- Nodes with only interpetiolar lines, not flaps.....................................................................................................................................8

7. Internodes quadrangular and 4-winged (Fig. 3D); petioles with abaxial tuberculate projections (rarely horn-shaped) on the transition zone from the petiole to the midvein (Fig. 3H) .............................................................................................................. M. tetragona

- Internodes terete-quadrangular; petioles with abaxial liguliform projections on the transition zone from the petiole to the midvein (Fig. 3G) ........................................................................................................................................................................ M. sanguinea

8. Branches, petioles, and both leaf surfaces hirsute (Fig. 4J); antesepalous stamen connectives with dorso-basal appendages laterally expanded............................................................................................................................................................................. M. hirsuta

- Branches, petioles, and abaxial leaf surfaces moderately to densely setulose (Fig. 4H); stamen connectives from both cycles with dorso-basal appendages not laterally expanded .................................................................................................................. M. radula

9. Antepetalous stamens with inflated (bulbous) connectives (Fig. 6H)..............................................................................................10

- Stamens from both cycles without inflated (bulbous) connectives ..................................................................................................13

10. Leaf blades subpeltate to peltate (Fig. 4K), and more than 8.4 cm wide .........................................................................................11

- Leaf blades neither subpeltate nor peltate, less than 8.1 cm wide....................................................................................................12

11. Leaf blades 22.8–28.7 × 13.3–16.7 cm, peltate, abaxial surfaces pubescent to setulose .................................................... M. peltata

- Leaf blades 17.2–27.7 × 8.1–15.5 cm, subpeltate, abaxial surfaces puberulent ...................................................... M. ninakurorum

12. Leaf abaxial surface densely pubescent, the trichomes evenly covering the entire surface (Fig. 4F); petals fuchsia to light fuchsia; antepetalous stamen connectives without dorsal appendages ................................................................................... M. bicentenaria

- Leaf abaxial surface sparsely to densely puberulent, the trichomes not covering the entire surface; petals reddish-purple; antepetalous stamen connectives with blunt ascending dorsal appendages ..................................................................................... M. franciscana

13. Stamens strongly dimorphic (connectives with different shapes, sizes and colors), antepetalous stamen connectives with apically trilobed (Fig. 6F) or sagittate ascending dorsal appendages ............................................................................................................14

- Stamens dimorphic (connectives with different shapes and sizes but with similar colors) or isomorphic, stamen connectives from both cycles without dorsal appendages (Fig. 6A), with dentiform dorsal appendages (Fig. 6E), with blunt ascending dorsal appendages (Fig. 6B) or dorsal appendages as mere humps (Fig. 6C and 6D)................................................................................15

14. Petioles with adaxial and lateral liguliform projections on the apex; corolla white; antepetalous stamen connectives with apically trilobed ascending dorsal appendages (Fig. 6F) ............................................................................................................ M. microflora

- Petioles without projections; corolla fuchsia; antepetalous stamen connectives with apically sagittate ascending dorsal appendages ...................................................................................................................................................................... M. urceolata

15. Corolla campanulate, pink-orange to reddish-orange (except fuchsia in M. vasquezii and red in M. rubriflora) (Fig. 3J).............16

- Corolla spreading, fuchsia to reddish-purple (Fig. 3I) .....................................................................................................................22

16. Calyx calyptrate or subcalyptrate, with irregular dehiscence (Fig. 5F) ...........................................................................................17

- Calyx neither calyptrate nor subcalyptrate, with regular dehiscence ...............................................................................................20

17. Calyx calyptrate, without dorsal projections....................................................................................................................................18

- Calyx subcalyptrate, with dorsal projections 0.5–3 mm long (Fig. 5F) ...........................................................................................19

18. Inflorescences with flowers in regular dichasia (3-flowered) in the branchlet ends; petals 20–24 mm long ............... M. tomentosa

- Inflorescences with flowers in 5–6-flowered umbels in the branchlet ends; petals 9–10 mm long...................................... M. acida

19. Leaf blades 10.8–12.7 × 2.7–3 cm, abaxial surface sparsely to moderately puberulent, trichomes not covering the entire surface... ............................................................................................................................................................................................. M. juanjil

- Leaf blades 16.5–23.5 × 9.3–10.7 cm, abaxial surface densely villose, evenly covering the entire surface .................. M. vasquezii

20. Nodes with robust interpetiolar flaps; inflorescences pendulous; calyces with obsolete dorsal projections ................. M. rubriflora

- Nodes without interpetiolar flaps; inflorescences erect; calyces with claw-shaped dorsal projections (Fig. 5D) ...........................21

21. Abaxial leaf surface tomentose with whitish to cream trichomes when dry; petals 19.5–24 mm long ................................ M. dazae

- Abaxial leaf surface pubescent with ferrugineous trichomes when dry; petals 13–15.5 mm long.............................. M. bongarana

22. Calyx calyptrate, with circumscissile dehiscence (Fig. 5G)....................................................................................... M. escalerensis

- Calyx not calyptrate, with regular dehiscence..................................................................................................................................23

23. Stamens dimorphic; antesepalous stamen connectives with descending dorso-basal appendages laterally expanded (Fig. 6I) .....24

- Stamens isomorphic; stamen connectives from both cycles with descending dorso-basal appendages not laterally expanded......28

24. Leaves subsessile (petioles up to 3 mm long), base auriculate .............................................................................. M. amischophylla

- Leaves with petioles longer than 8 mm, base acute, attenuate, or obtuse (rarely broadly obtuse in M. weberbaueri)....................25

25. Stamen connectives without dorsal appendages......................................................................................................... M. weberbaueri

- Stamen connectives with blunt ascending dorsal appendages (Fig. 6B)..........................................................................................26

26. Hypanthium 10-costate, with longitudinal ridges up to 2.5 mm high (Fig. 5I)............................................................... M. sumatika

- Hypanthium terete, without ridges ...................................................................................................................................................27

27. Inflorescences, hypanthia, and calyces densely tomentose, the trichomes up to 1.5 mm long......................................... M. vargasii

- Inflorescences, hypanthia, and calyces sparsely to densely furfuraceous, the trichomes up to 0.25 mm long (Fig. 4D) .................... ............................................................................................................................................................................... M. vilcabambensis

28. Nodes with robust interpetiolar flaps (sometimes small in M. callosa) (Fig. 3B) ...........................................................................29

- Nodes without interpetiolar flaps .....................................................................................................................................................31

29. Internodes quadrangular and 4-winged; stamen connectives with blunt ascending dorsal appendages (Fig. 6B) ..... M. megaphylla

- Internodes quadrangular, but not winged; stamen connectives with dorsal appendages as mere humps or obsolete......................30

30. Petioles 25–50 mm long, with an adaxial projection (scutum) on the transition zone from the petiole to the midvein (Fig. 3E)....... ...................................................................................................................................................................................... M. zunacensis

- Petioles 10–22 mm long, without projections ..................................................................................................................... M. callosa

31. Petioles with an apical adaxial projection (Fig. 3F); petals abaxially moderately to densely puberulent ........................... M. drakei

- Petioles without projections; petals glabrous ...................................................................................................................................32

32. Leaf blades with entire margins, and the adaxial surfaces flat.........................................................................................................33

- Leaf blades with denticulate margins, and the adaxial surfaces flat to bullate ................................................................................34

33. Flowers 6-merous; calyx without dorsal projections (Fig. 5A)............................................................................................. M. neillii

- Flowers 5-merous; calyx with thick, callose dorsal projections........................................................................................... M. rigida

34. Leaf venation with 1 pair of secondary veins (lateral nerves) and an additional pair of faint submarginal veins.............. M. rugosa

- Leaf venation with 2 pairs of secondary veins (lateral nerves) and an additional pair of faint submarginal veins .........................35

35. Internodes quadrangular and 4-winged, wings 1–3.5 mm high (Fig. 3C); calyx with callose dorsal projections, whitish and much lighter than the rest of the calyx and hypanthium when dry (Fig. 5C)...................................................................... M. penningtonii

- Internodes quadrangular, without wings; calyx with small conic dorsal projections, of the same color as the rest of the calyx and hypanthium when dry ................................................................................................................................................... M. tetraquetra