Arthothelium, A. Massalongo, 1852

Broeck, Dries Van Den, Tehler, Anders, Razafindrahaja, Tahina & Ertz, Damien, 2017, Four new species of Arthothelium (Arthoniales, Ascomycetes) from Africa and Socotra, Phytotaxa 331 (1), pp. 51-64 : 59-60

Key to the species of Arthothelium ( Mycarthothelium included) reported from tropical Africa and Socotra

The key is based on the protologues, information on JSTOR (http://plants.jstor.org), other literature (e.g. Willey 1890; Makhija &Patwardhan 1995a, 1995b; Sundin 1999; Grube2007; Smith et al. 2009) as well as on the study of the following type species: Arthothelium abnorme (BM!), Arthonia albopulvurea (H!), Arthothelium aurantiacum Müller Argoviensis (1890: 345) (G!), A. beccarianum Bagliettto (1875: 252) (M!), A. consanguineum Müller Argoviensis (1888b: 207) (G!), A. desertorum (KR!, STU!), A. distentum ( Vainio 1901: 446) Zahlbruckner (1922: 125 in Zahlbruckner 1924) (BM!, TUR!), A. emersum (G!), A. homoeophanum ( Nylander 1863b: 236) Zahlbruckner (1922: 126 in Zahlbruckner 1924) (H!), A. loandense (BM!), A. macrothecum (G!), A. variabile (WU!), Mycarthothelium angustissimum (TUR!) and M. limae Vainio (1930: 169 in Vainio 1929 –1930) (TUR!). According to the protologue, the hymenium of A. distentum reacts I+ blue while that of A. macrothecum is I + red. A study of the type of A. distentum present in BM (the type of TUR is an oligotype, so we did not perform a destructive analysis) revealed an hymenium I+ blue but turning into red. A. distentum is similar in all other aspects to A. macrothecum and has therefore been reduced in synonymy with the later. Makhija & Patwardhan (1995a) considered A. consanguineum to be conspecific with A. emersum but we prefer to keep them as different species because their types specimens appears too different.

1. Hypothecium or ascomata red ......................................................................................................................................................... 2.

- Hypothecium or ascomata not red ................................................................................................................................................... 3.

2. Ascomata black; hypothecium with red pigment, K+ purplish; hymenium I+ red; ascospores not exceeding 20 μm in length, becoming dark brown .................................................................................................................................... Arthothelium atrorubrum

- Ascomata red; hypothecium without red pigment; red pigment in epihymenium K+ pale brown; hymenium I+ blue; ascospores exceeding 20 μm in length, persistently hyaline ...................................................................................... Arthothelium sanguineum

3. Ascomata orange pruinose, K+ purplish ................................................................................... Arthothelium aurantiacopruinosum

- Ascomata not orange pruinose, K– ................................................................................................................................................. 4.

4. Thallus orange ......................................................................................................................................... Arthothelium aurantiacum

- Thallus not orange ........................................................................................................................................................................... 5.

5. Ascospores with one or two larger terminal cells ............................................................................................................................ 6.

- Ascospores without larger terminal cell(s) .................................................................................................................................... 10.

6. Ascospores with two larger terminal cells ....................................................................................................... Arthothelium feuereri

- Ascospores with one larger terminal cell ........................................................................................................................................ 7.

7. Ascospores not exceeding 30 (–35) μm in length ....................................................................................... Arthothelium loandense

- Ascospores exceeding 30 (–35) μm in length ................................................................................................................................. 8.

8. Ascomata irregular to very much elongate; hymenium I+ blue ................................................................. Arthothelium corticatum

- Ascomata rounded to slightly elongate; hymenium I+ red ............................................................................................................. 9.

9. Thallus white to greenish; ascomata brownish-black; epihymenium brown; ascospores transversely 6–8-septate, 19–24.5 μm broad.......................................................................................................................................................... Arthothelium frischianum

- Thallus whitish grey to grey; ascomata black; epihymenium olive-green; ascospores transversely 7–11-septate, 9.9–20 μm broad ............................................................................................................................................................................ Arthothelium bessale

10. Ascospores not exceeding 30 (–35) μm in length ......................................................................................................................... 11.

- Ascospores exceeding 30 (–35) μm in length ............................................................................................................................... 18.

11. Hymenium I+ persistently blue ..................................................................................................................................................... 12.

- Hymenium I+ blue, turning rapidly into red ................................................................................................................................. 14.

12. Ascomata distinctly grey-pruinose ............................................................................................................ Arthothelium desertorum

12. Ascomata epruinose, with or without remnants of thallus ............................................................................................................ 13.

13. Ascomata with or without remnants of thallus, irregularly rounded to short lirelliform; asci with KI+ blue ring like structure in the tholus; ascospores hyaline but becoming brown, 14–24 × 7–12 μm ....................................................... Arthothelium beccarianum

- Ascomata without remnants of thallus, lirellate; asci without blue ring like structure in the tholus; ascospores hyaline (over aged spores slightly brownish), 14–19 × 5.5–8 μm...................................................................................... Arthothelium consanguineum

14. Ascomata rounded to elliptical, strongly emergent to almost adnate ............................................................ Arthothelium emersum

- Ascomata lirellate, stellate, branched or cerebriform, immersed to erumpent .............................................................................. 15.

15. Ascomata brown to yellowish, greyish pruinose, stellate to cerebriform .......................................................... Arthothelium miesii

15. Ascomata dark brown to black ...................................................................................................................................................... 16.

16. Ascomata immersed; ascospores 20–32 μm, becoming brown and ornamented with brown dots ............... Arthothelium variabile

16. Ascomata immersed to semisessile; ascospores 9–21.5 μm, persistently hyaline ........................................................................ 17.

17. Ascospores with (6–)7 transversal and 1–2 longitudinal septa; asci without blue ring like structure in the tholus ............................ ........................................................................................................................................................ Mycarthothelium angustissimum

- Ascospores with 3–5 transversal and 0–1 longitudinal septa; asci with KI+ blue ring like structure in the tholus ............................ ...................................................................................................................... Arthonia albopulvurea (= Arthothelium crozalsianum )

18. Epihymenium K+ violet; asci without blue ring like structure in the tholus ...................................... Arthothelium homoeophanum

- Epihymenium K– or K+ olivaceous; asci with KI+ blue ring like structure in the tholus ............................................................ 19.

19. Lichenized; ascomata 0.5–1.5 × 0.5–0.75 mm; epihymenium K+ olivaceous; ascospores hyaline becoming brown ........................ ................................................................................................................................................................. Arthothelium macrothecum

- Not lichenized; ascomata 0.2–0.7 × 0.2–0.5 mm; epihymenium K–; ascospores persistently hyaline ........ Mycarthothelium limae