Key to the species of Prestonia from Peru

1. Corolla tube and lobes pubescent outside, the indument ferruginous, yellow to yellowish-brown; intra- or interpetiolar colleters conspicuous .............................................................................................................................................. 2

- Corolla tube and lobes glabrous or minutely and inconspicuously puberulent outside (P. vana), the indument not ferruginous or yellow; intra– or interpetiolar colleters inconspicuous ............................................................................. 6

2. Free corona lobes inserted about the midway of the corolla tube, the apices always included; sepals 2.5–4.0 mm long; corolla tube 4–6 mm long ....................................................................................... P. parviflora (Benth.) Benth.

- Free corona lobes inserted near the corolla mouth, the apices exserted or at least attaining level of the mouth; sepals 7.0–19.0 mm long; corolla tube 11–19 mm long ......................................................................................................... 3

3. Leaves hirsute abaxially, trichomas erect .................................................................................. P. ipomaeifolia A.DC.

- Leaves not hirsute abaxially, trichomas irregularly adpressed ................................................................................... 4

4. Inflorescence basally branched, the branches short, sometimes hide behind the bracts; follicles minutely and inconspicuously sericeous; seeds 15–22 mm long ....................................................................... P. surinamensis Müll.Arg.

- Inflorescence unbranched; follicles conspicuously hirsute or hispid; seeds 8–14 mm long ...................................... 5

5. Inflorescence a dichasial cyme, simple and elongate; follicles 15–18 cm long .................... P. racemosa J.F.Morales

- an umbeliform cyme, agglomerate; follicles 5–13 cm long ........................................................... P. tomentosa R.Br.

6. Corolla tube lacking corona lobes inside..................................................................................................................... 7

- Corolla tube with corona lobes inside ......................................................................................................................... 9

7. Bracts 5.0–25.0(–30.0) mm long, foliaceous to subfoliaceous; corolla lobes pinkish–yellow, reddish–yellow to purplish–yellow; sepals (8.0–)10.0–22.0 mm long ............................................................ P. riedelii (Müll.Arg.) Markgr.

- Bracts 0.7–3.0 mm long, scarious; corolla lobes cream to yellow; sepals 2.9–8.0 mm long ...................................... 8

8. Corolla tube 11.0–17.0 mm long; anthers 4.5–6.0 mm long ............................................... P. coalita (Vell.) Woodson

- Corolla tube 7.5–8.5 mm long; anthers 3.1–3.3 mm long … P. succo J.F.Morales

9. Free corona lobes inserted about the midway of the corolla tube, the apices always included ................................ 10

- Free corona lobes inserted near the corolla mouth, the apices exserted or at least reaching the mouth ................... 12

10. Sepals 1–3(–4) mm long, the apex usually reflexed; inflorescence unbranched … P. quinquangularis (Jacq.) Spreng.

- Sepals (8–) 9–18 mm long, the apex not reflexed; inflorescence branched, the branches short, but visible .............. 11

11. Bracts 1.0–5.0 × 0.5–1.0 mm, scarious; leaf blades 4.5–22.0 cm wide, coriaceous; wet forest ................................... ............................................................................................................................................... P. annularis (L.f.) G.Don

- Bracts 7.0–11.0 5 3.0–4.0 mm, foliaceous; leaf blades 1.6–4.0 cm wide, membranaceous; dry forest ........................ .............................................................................................................................. P. parvifolia K.Schum. ex Woodson

12. Leaf blades membranaceous; tertary veins not impressed; dry forest ................................................. P. mollis Kunth

- Leaf blades coriaceous; tertary veins impressed and conspicuous; wet forest .......................................................... 13

13. Leaves densely ferruginous–puberulent abaxially; follicles densely and minutely ferruginous–tomentulose ............... ........................................................................................................................................ P. megagros (Vell.) Woodson

- Leaves glabrous, or inconspicuously and sparsely puberulent and glabrescent abaxially ........................................ 14

14. Sepals mostly 3.0–8.0 × 1.0– 2.5 mm ....................................................................................... P. plumierifolia Markgr.

- Sepals mostly 10.0–21.0 × 3.0–8.0 mm .................................................................................................................... 15

15. Corolla tube minutely and conspicuously puberulent outside; follicles winged, divaricate ............. P. vana Woodson

- Corolla tube glabrous or inconspicuously papillate outside; follicles not winged or divaricate ............................... 16

16. Bracts 4.0–26.0 × 2.0–6.0 mm, foliaceous ................................................................................................................. 17

- Bracts 1.0–2.5 × 0.5–1.0 mm, scarious ...................................................................................................................... 18

17. Follicles 4–9 mm wide, seeds 14–16 mm long; bracts 8–25 mm long ............. P. rotundifolia K.Schum. ex Woodson

- Follicles 11–13 mm wide, seeds 18–21 mm long; bracts 4–7 mm long ............................................. P. robusta Rusby

18. Inflorescence and young branchlets minutely and densely ferruginous-puberulent ................ P. amabilis J.F.Morales

- Inflorescence and young branchlets glabrous or inconspicuously puberulent and glabrescent ................................ 19

19. Follicles membranaceous, 6–8 mm wide; inflorescences conspicuously branched, nectary totally covering ovary ..... ................................................................................................................................ P. portobellensis (Beurl.) Woodson

- Follicles woody, 8–11 mm wide; inflorescences inconspicuously branched; nectary not covering ovary ................... .......................................................................................................................................... P. trifida (Poepp.) Woodson