Epipactis atrorubens (Hoffmann, 1804) Besser, 1809

Brullo, Salvatore, Brullo, Cristian, Cambria, Salvatore, Tavilla, Gianmarco, Pasta, Salvatore, Scuderi, Leonardo & Zimmitti, Angelo, 2021, A new subspecies of Epipactis microphylla (Orchidaceae; Epidendroideae) from Pantelleria Island (Sicily), Phytotaxa 512 (2), pp. 83-96 : 92

Key to the species of the Epipactis atrorubens group

1. Stem densely pubescent, cauline leaves 3–5 (rarely more)................................................................................................................2

- Stem glabrous basally and pubescent higher up, cauline leaves (4)5–11...........................................................................................4

2. Leaf longer than internode, back of sepals and petals whitish green, hypochile 4.0– 5.5 mm wide, epichile scalloped marginally, viscidium absent, ovary not pyriform........................................................................................................................ E. krymmontana

- Leaf shorter than internode, back of sepals and petals green tinged with red or purple, hypochile 3.0–4.0 mm wide, epichile crenulated marginally, viscidium present, ovary pyriform.................................................................................................................3

3. Cauline leaves 1.5–2.2 mm wide, leaf margin with 14–15 teeth per mm, back of sepals and petals glabrous or sparsely pubescent, dorsal sepal with 2 nerves, epichile 5–6 mm wide, ovary 9–12 mm long ..................................... E. microphylla subsp. cossyrensis

- Cauline leaves 0.5–1.5(2.0) mm wide, leaf margin with 10–12 teeth per mm, back of sepals and petals pubescent, dorsal sepal with 1 nerve, epichile 3–4 mm wide, ovary 6–9 mm long .................................................................... E. microphylla subsp. microphylla

4. Sepals with 4–5 nerves, lateral sepals 5–7 mm wide, petals 9.0–10.0 × 5.0–6.0 mm, anther brown ........................... E. condensata

- Sepals with 1–3 nerves, lateral sepals 2–5 mm wide, petals 3.5–9.0 × 2.0– 4.5 mm, anther yellow to greenish yellow ...................5

5. Back of sepals subglabrous, front of petals glabrous, epichile yellow to pink, 5.0–6.0 mm wide, margin scalloped .. E. spiridinovii

- Back of sepals pubescent, front of petals pubescent to subglabrous, epichile dark purple to violet, 3.0– 4.5 mm wide, margin denticulate to crenulate.......................................................................................................................................................................6

6. Hypochile 2.0–3.0 mm wide ................................................................................................................................................ E. kleinii

- Hypochile 3.8–4.5 mm wide ..............................................................................................................................................................7

7. Sepals 5–6 mm long, dorsal sepal 2.5–3.0 mm wide, lateral sepals with 3 nerves, petals 4.0–5.0 mm long ................. E. subclausa

- Sepal 6–10 mm long, dorsal sepal 3.5–5.0 mm wide, lateral sepals with 2 nerves, petals 5.5–9.0 mm long....................................8

8. Basal bracts 10–30 mm long, flowers usually dark red to purple, lateral sepals 2.5–4.0 mm wide, petals 2.5–3.5 mm wide, back pubescent, laterally 2 nerved, ovary 4–6 mm long......................................................................................................... E. atrorubens

- Basal bracts 30–60 mm long, flowers usually greenish yellow, lateral sepals 4.5–5.0 mm wide, petals 4.0– 4.5 mm wide, back subglabrous, laterally 3 nerved, ovary 6–8 mm long .......................................................................................................... E. cardina