Key to the currently recognized species of Atheris (adapted and updated from Spawls & Branch 2020)

1a Subcaudals fewer than 22.................................................................. Atheris barbouri

1b Subcaudals more than 22............................................................................... 2

2a Predominantly brown with very prickly head scales; found west of Ghana ............................. Atheris hirsuta

2b Does not have the above combination of characters.......................................................... 3

3a Ventral scales fewer than 138; found south of 15ºS, in Mozambique ............................... Atheris mabuensis

3b Ventral scales usually more than 138; north of 15ºS.......................................................... 4

4a Lateral scales serrated................................................................................. 5

4b Lateral scales not, or only feebly and irregularly, serrated..................................................... 10

5a Supraocular scales forming elongate “horns”............................................................... 6

5b No supraocular “horns”................................................................................ 7

6a Up to 20 transverse head scales; occurs from Udzungwa Mountains northwards in Tanzania .......... Atheris ceratophora

6b Up to 28 transverse head scales; occurs south of the Udzungwa Mountains in Tanzania .................. Atheris matildae

7a Four suprarostral scales in first (or only) row; dorsals rounded at the apex; each dorsal scale tipped with yellow;................................................................................................. Atheris desaixi

7b Three to five suprarostrals in first (or only) row; dorsals pointed at apex; dorsal scales not tipped with yellow;........... 8

8a Gular scales strongly keeled; lateral scale rows 4–6 weakly serrated; dorsum yellow-brown to purple-brown with dark-centred, pale yellowish rhombic vertebral markings.................................................. Atheris katangensis

8b Gular scales smooth or feebly keeled; lateral scale rows 2–6 or –8 strongly keeled; dorsum green with irregular black markings or green to blackish with symmetrical yellow markings....................................................... 9

9a Scales on top of head anteriorly smooth or feebly keeled; 18–20 scales across back of head between posterior supralabials; dorsal body scales with keels extending to the tip; green with variable black markings.................. Atheris nitschei

9b Scales on top of head anteriorly strongly keeled; 24–26 scales across back of head between posterior supralabials; dorsal body scales with keels not extending to the tip; dorsum dark green to blackish, often with symmetrical yellow markings on back of head and zigzag yellow dorsolateral lines and spots........................................... Atheris rungweensis

10a Scales across top of head between posterior supralabials usually more than 23; midbody scale rows 25–36. Atheris chlorechis

10b Scales across top of head between posterior supralabials fewer than 23; midbody scale rows 14–25................... 11

11a Scales on neck lanceolate or acuminate; lateral scale rows 2–5 frequently fused; scales across top of head between posterior supralabials 10–12................................................................................... 12

11b Scales on neck not lanceolate or acuminate; lateral scale rows 2–5 frequently duplicated; scales across top of head between posterior supralabials 15–20........................................................................... 13

12a Three large suprarostrals; interorbitals 6–10, strongly keeled; two scales between eye and nasal; supralabials 9–10; midbody scale rows 15–18; lanceolate dorsal scales do not extend beyond midbody............................ Atheris hispida

12b Two very large suprarostrals; five interorbitals, median ones feebly keeled; a single scale between eye and nasal; six supralabials; midbody scale rows 14; lanceolate dorsal scales extend beyond midbody....................... Atheris acuminata

13a Scales across top of head between posterior supralabials 15–18............................................... 14

13b Scales across top of head between posterior supralabials 19–20............................. Atheris hetfieldi sp. nov.

14a Underside checked black, blue and white; dark postocular stripe present............................ Atheris broadleyi

14b Underside not checked black, blue and white; dark postocular stripe not always present............................ 15

15a Usually at least one labial scale in contact with the orbit....................................... Atheris subocularis

15b Usually no labial scale in direct contact with the orbit....................................................... 16

16a Anterior subcaudals entire, posterior divided................................................ Atheris mongoensis

16b Subcaudals entire.................................................................................... 17

17a Five suprarostrals, three scales between nasal and eye.......................................... Atheris anisolepis

17b Thre suprarostrals, two scales between nasal and eye......................................... Atheris squamigera