Introduction
Despite its rather young age, Réunion is a lichenologically most interesting island, home to a number of endemic species, particularly in the Pannariaceae (Jørgensen et al. Reference Jørgensen, van den Boom and Sérusiaux2009). The second author visited the island in 2009 and collected several interesting specimens of the Pannariaceae, which have been revised by the first author. Among them was a very unusual looking collection, at first sight reminiscent of the West-Indian Pannaria caesiocinerea (Vain.) P. M. Jørg., but on closer inspection proving to contain no secondary lichen substances and to have an amyloid, internal apical ring-structure (Fig. 1C), both characters clearly placing it in Parmeliella, in spite of the squamulose thalline margin of the apothecia. It certainly belongs in that little group of species where the newly described Parmeliella zeylanica P. M. Jørg. is placed (Jørgensen Reference Jørgensen2009), which may prove to need acceptance on some level, but at the moment is best kept within the genus Parmeliella. The specimen from Réunion is clearly different from any other in this mainly Indo-pacific group (see below), and is accordingly described as new.
Parmeliella borbonica. A, habitus; B, anatomy of the apothecium; C, an ascus in Lugol's iodine. Scales: A = 5 mm; B = 100 µm; C = 10 µm.
Material and Methods
The material is that cited below and the methods are the same as in previous papers by the first author.
The New Species
Parmeliella borbonica P. M. Jørg. & F. Schumm sp. nov
Parmeliellae zeylanicae similis, sed thallo tenue, applanato et caesiocinereo, medulla incolorata et sporis magnis, 10–15 × 8–10 µm.
Typus: La Réunion, Takamaka, low mountain forest near the electrostation, alt. 790 m, 10 September 2009, J.-P. Frahm & F. Schumm (BG—holotypus!; hb. Schumm 15265—isotypus).
(Fig. 1)
Thallus bluish grey with whitish margins, squamulose, forming appressed, orbicular patches, up to 3 cm diam. of imbricating lobes, centrally nearly crustose, marginally up to 3 mm broad, 60–100 µm thick with a paraplectenchymatous upper cortex. The blackish prothallus is poorly developed, mostly crustaceous and not extending beyond the marginal lobes. Upper cortex distinct, cellular 15–25 µm wide, upon a loose medullary layer, enclosing packets of Nostoc, individual cells of which measure 3–5 µm diam. Lower cortex absent.
Apothecia laminal, sessile, up to 1·5 mm diam., often aggregated in groups, disc light brown, flat; margins wavy to slightly lobed with thalline squamules attached. Hymenium 100–125 µm high, I+ blue, made up of simple, septate hyphae, apically thickened with external brown pigment. Asci narrowly subcylindrical, 70–80 × 6–10 µm, apically with internal amyloid ring-structure (Fig. 1), 8-spored. Ascospores subglobose, simple, colourless, 10–15 × 8–10 µm with fairly smooth exospore without extensions.
Conidiomata not observed.
Chemistry. All reactions negative. No lichen substances or pigments detected by TLC.
Additional specimen examined. La Réunion: NE of Plaine-des-Palmistes, trail E of lake ‘Grand Étang’, from parking lot to the lake in sloping W-exposed, tropical rainforest on guave, alt. 570 m, 2008, P. & B. van den Boom, A. M. Brand, E. Sérusiaux 40037 (hb. P. v.d. Boom).
Ecology and distribution. As yet known only from two localities, and possibly an endemic. The type grows on an old tree in a wet, lowland forest at 790 m altitude near the beginning of the trail that leads down from the station Belvédere (EDF electro power station) to the reservoir Takamaka. This steep, north side of the Rivière des Maison canyon, where also Grand Étang (the other collection) is situated, is one of the two wettest regions in the east of Réunion (annual rainfall 7 m). In the vicinity numerous species of the Coccocarpiaceae, Collemataceae (e.g., Leptogium denticulatum auct.), Pannariaceae and Stictaceae (e.g., Pseudocyphellaria desfontainii (Delise) D. J. Galloway) occur, with the commonest foliose lichen in that locality being Sticta caperata (Nyl.) Bory, a palaeotropical species described from Réunion. Remarkable occurrences here are the very rare Coccocarpia imbricascens Nyl., which until recently was known only from its unlocalized type (Arvidsson Reference Arvidsson1983), but has since been discovered in South America (Lücking et al. Reference Lücking, Aptroot, Chaves, Sipman and Umara2007), as well as the palaeotropical Coccocarpia smaragdina Pers., and the endemic Pannaria multifida P. M. Jørg. (Jørgensen Reference Jørgensen2004). The concentration of rare and endemic species, mostly with palaeotropical affinity, in this locality is most possibly due to the rarity of this kind of lowland forest, which has been cleared away in most of the neighbouring islands (e.g., Madagascar and Mauritius), but is still present on the steep mountain-sides in Réunion where obviously many of the once presumably more widespread, palaeotropical species are still to be found. This is confirmed by the occurrence in the second locality, which is also in a lowland, moist tropical forest, close to the type locality of Pannaria multifida.
Notes. In spite of the external Pannaria-like appearance, the bluish grey thallus and apothecia with thalline margins, this is a Parmeliella as is obvious from the lack of pannarin in the thallus, and above all by the internal apical apparatus of the asci which is amyloid and forms a ring-structure (Fig. 1C), most typical of the genus Parmeliella. This genus typically (traditionally) has no thalline margin of the apothecia, although this character is now known to be of little taxonomic value. There are quite a few similar species, mainly tropical, with these characteristics, the Parmeliella mariana group, most of which form large, circular thalli with spreading marginal lobes, resting on a conspicuous mat of rhizohyphae, usually called a hypothallus. There are also a few more squamulose taxa, mostly in the Indo-pacific region, to which this species is most closely related, though it probably reminds one mostly of the South American Parmeliella imbricatula (Müll. Arg.) P. M. Jørg. (a species belonging in the P. mariana group), which has a thicker thallus of more discrete squamules and more regular, strongly margined apothecia (see Jørgensen Reference Jørgensen2003), with narrower, ellipsoid spores. It is definitely closer to the two brownish species from Sri Lanka. The equally small-squamulose Parmeliella zeylanica P. M. Jørg. has a looser thallus with yellowish medulla and smaller spores. In many ways P. borbonica appears to be closest to P. leiostroma (Nyl.) P. M. Jørg., owing to the thin, adnate thallus, which in that species is brownish and rests on a distinct mat of brownish rhizohyphae. The spores of that species are also ellipsoid and narrower than in P. borbonica. These species appear to form a neat group, the most widespread species of which is P. endomilta Vain., a brownish species with a thin thallus and an orange medulla and citriform spores, distributed throughout the region of the Indian Ocean eastwards to New Guinea (Jørgensen & Sipman Reference Jørgensen and Sipman2006). A key to the members of this highly characteristic group, which may prove to be in need of a higher taxonomic rank, is presented below.
Key to Parmeliella endomilta and allies
1 Thallus bluish grey, medulla always unpigmented ... 2
Thallus brownish, medulla often pigmented ... 3
2(1) Thallus cracked, on a distinct hypothallus; spores narrowly ellipsoid, 12–15 ×5–6 µm; South America ... Parmeliella imbricatula (Müll. Arg.) P. M. Jørg.
Thallus continuous, no hypothallus visible; spores subglobose, 10–15 × 8–10 µm; Réunion ... Parmeliella borbonica P. M. Jørg. & F. Schumm
3(1) Thallus with yellow or orange medulla, hypothallus indistinct ... 4
Thallus with unpigmented medulla, hypothallus distinct; Sri Lanka ... ... Parmeliella leiostroma (Nyl.) P. M. Jørg.
4(3) Thallus skin-like, more or less continuous, medulla orange, spores citriform, hypo- thallus indistinct; widespread in Indo-Pacific region ... ... Parmeliella endomilta Vain.
Thallus discretely squamulose, medulla pale yellow, hypothallus indistinct, spores drop-like; Sri Lanka ... Parmeliella zeylanica P. M. Jørg.
We are indebted to the curators of BM and G, and Pieter van den Boom who sent us material on loan. F. Schumm would like to express his thanks to André Aptroot for continuous support and encouragement in his work on tropical lichens.
