Introduction
Lichenicolous fungi have been studied for more than 200 years (Hawksworth Reference Hawksworth2003; Lawrey & Diederich Reference Lawrey and Diederich2003), and amongst the earliest recognized was Lichen parasiticus Sm. 1808, now known as Abrothallus parmeliarum (Sommerf.) Arnold 1874. The genus Abrothallus De Not. 1845 itself was amongst the first few generic names introduced for obligately lichenicolous fungi (De Notaris Reference De Notaris1845, Reference De Notaris1846), and was monographed by Lindsay (Reference Lindsay1857) who treated it in a broad sense to include a wide range of lichenicolous fungi. Modern usage follows the circumscription of Kotte (Reference Kotte1909). The genus is characterized by having more or less convex apothecioid ascomata which lack an obvious exciple, and are often covered with greenish pruina; the asci are fissitunicate, with four to eight, 2–4-celled, dark brown or greenish asymmetric ascospores with an evident ornamentation, sometimes separating into part-spores; the interascal filaments are ramified to anastomosed paraphyses; the epithecial layer contains granules which can dissolve in potassium hydroxide, and the anamorph, where known, belongs to Vouauxiomyces Dyko & D. Hawksw. 1979. The placement of the genus within the Ascomycota is uncertain pending molecular sequence data. Species of the genus are found on various foliose and fruticose lichens, including several genera from the family Parmeliaceae, from the suborder Peltigerinae, and the genera Ramalina, Stereocaulon and Cladonia.
Despite its long history, the infrageneric taxonomy has remained controversial, especially with regard to host-specificity, and new taxa continue to be described (Wedin Reference Wedin1994; Cole & Hawksworth Reference Cole and Hawksworth2001; Etayo Reference Etayo2002; Diederich Reference Diederich2003; Etayo & Osorio Reference Etayo and Osorio2004; Hafellner et al. Reference Hafellner, Herzog and Mayrhofer2008). There are 57 names in the genus listed in Index Fungorum (http://www.indexfungorum.org, consulted 3 June 2010), of which 23 species of Abrothallus are currently accepted, although the species concepts of those occurring on parmelioid lichens merit more critical study, including molecular phylogenetic methods. Four species are known growing on Peltigerales, namely Abrothallus welwitschii Tul. Reference Tulasne1852, A. secedens Wedin & R. Sant. Reference Wedin1994, A. granulatae Wedin Reference Wedin1994 and A. stictarum Etayo Reference Etayo2002. Here we describe a further new species from Peltigerales growing on Lobaria, an additional host genus for Abrothallus.
Material and Methods
The material examined is deposited in M, MAF and UPS. The morphological characters of dry herbarium specimens were studied under a Leica S4E and Zeiss Stemi SV11 dissecting microscope using standard techniques. Microscopic characters were examined with a Leica DM750 and Zeiss Axioskop2plus research microscope using razor-blade-cut sections mounted in water and mounted in c. 5% KOH (K) solution. The colour reactions were observed using 50% NH3 (N), K and Lugol's iodine solution (I), the latter both with (K/I) and without pre-treatment with K. Photographs were taken with a Canon PowerShot G2 digital camera attached to the microscopes. All photomicrographs were taken in water.
The sizes of ascopores, asci, cells of the hypothecium and ascomata are presented as: minimum value – (average) – maximum value. All size values of microscopical characters were measured in the holotype in water.
Taxonomy
Abrothallus halei Pérez-Ortega, Suija, D. Hawksw. & R. Sant., sp. nov.
MycoBank no.: MB 518660
Fungus lichenicola in genere Lobaria vigens. Ascomata apothecia, superficialia, convexa ad inflata, ad basim constricta, viridi-pruinosa, 200–(300)–550 µm diam. Asci clavati, bitunicati, octospori. Ascosporae ellipsoidae, brunneae, verruculosae, 3-septatae, secedentes, 9–(10·7)–14 × 3·2–(4·0)–5·0 µm.
Typus: USA, Minnesota, Lake Co., Superior National Forest, 14·5 km W of Tofte, east of Hare Lake, 47°36′N 91°02′W, elev. 550 m, mature sugar maple stand with some old Betula alleghaniensis, on Lobaria quercizans on bark of Acer saccharum, 28 July 1999, C. Wetmore 83138 (M-0151980—holotypus; isotypes are to be distributed in Triebel, Microfungi Exsiccati).
Fig. 1. Abrothallus halei. A, apothecia on necrotic apothecia of Lobaria quercizans, arrows point to apothecia; B, detail of an ascoma; C, a mature ascus with ascospores; D, paraphysis; E, young ascospore showing one septum; F – H, mature ascospores. C, D, E and G with differential inteference contrast. Scales: A & B = 150 µm; C = 25 µm; D – H = 2·5 µm.
Fig. 2. Abrothallus halei. A, ascus; B, ascospores. Scales: A = 10 µm; B = 3 µm.
Mycelium immersed, K/I−. Ascomata apothecioid, immersed when very young, soon superficial, on the host apothecia or thallus, convex to plane, black, intensively green pruinose, especially when young, the pruina sometimes disappearing in mature apothecia, width 200–(300)–550 µm, height c. 150 µm, constricted at the base, ± stipitate; epithecium with brown to dark brown pigment granules dissolving in K; hymenium c. 50 µm tall, hyaline in the lower part, with an olivaceous greenish pigment in the upper part, K+ green intensified, N±violet; exciple c. 60–70 µm wide in vertical section, composed of radiating septate hyphae; hypothecium pale brown, c. 50 µm tall, of rectangular cells, 5–(5·6)–6 × 4–(4·9)–6 µm. Interascal filaments dichotomously branched, c. 1·5 µm wide, the tip only slightly widened to 2–2·5 µm. Asci bitunicate in structure and fissitunicate, clavate, thickened at the apex, with a narrow internal apical beak when young, 40–(47·5)–60 × 9–(10)–12 µm, mainly 8-spored but some asci 4- or 6-spored. Ascospores brown, 4-celled when mature, young spores 2-celled, 9–(10·7)–14 × 3·0–(4·0)–5·0 (upper cell) / 3·0–(3·0)–4·0 (lower cell) µm (n = 20), asymmetrical, verruculose, strongly constricted at the middle septum, separating into two part-spores within the ascus when mature. Anamorph not observed.
Intraspecific variation. The morphological variation is mainly limited to the extent of the pruinosity over the surface of the ascomata. We also noted that in Cole 9293 (MAF), 6-spored asci dominated over 8-spored asci, while the opposite was noted in the other specimens. In the same specimen (Cole 9293), the hypothecium was also somewhat taller, up to c. 110 µm tall.
Hosts. So far, all extra-European specimens are recorded from Lobaria quercizans, while the single European collection is from L. pulmonaria. The species grows mainly on the apothecia of the host which turn black, most probably due to the action of the lichenicolous fungus. A darkening of the infected thallus area was also seen when L. pulmonaria was the host.
Etymology. The name was chosen based on the herbarium designation Abrothallus halei (as ‘A. haleii’ R. Sant. nom. prov.) coined but not published by R. Santesson, probablyin the 1960s. The epithet honours the American lichenologist, the late Mason E. Hale (1928–1990), who had a special interest in the Lobaria amplissima/L. quercizans complex (Hale Reference Hale1957) and distributed material of the new species in an exsiccate (see below).
Distribution. This new species is currently known from three localities in the USA (West Virginia, Maine, and Minnesota) and from one locality in Europe (Norway). Abrothallus halei may now be extinct in the Maine locality as an intensive search there by DLH on two occasions in 2008 failed to find the species again, several of the mature maples formerly present having been cut down as part of a road-improvement scheme, although Lobaria quercizans was still abundant on some of the remaining roadside trees.
Additional specimens examined. USA: West Virginia: Pocahontas Co., at Gaudier Knob, on apothecia of Lobaria quercizans, vii 1956, R. Santesson [Hale, Lichenes Americani Exsiccati no. 53, sub L. quercizans] (UPS: F-156131/450256); Maine, Hancock Co., Rt. 182, 7 miles west of Rt. 1, north shore of Tunk Lake, 44°27′36″N 67°55′58″W, on L. quercizans on Acer rubrum, M. S. Cole 9293 (MAF).—Norway: Sör-Tröndelag, Rissa, the valley of the river Sörelv, not far from the river Stavsletelv (c. 3 km E of Vollavatn), on thallus of L. pulmonaria on Salix caprea, 1961, R. Santesson 14334c (UPS: F-156140/450265).
Discussion
Attention was first drawn in print to this species by Santesson (in Hawksworth Reference Hawksworth1990) who gave ascospore measurements of 11–15 × 4–5 µm for the yet undescribed species. Abrothallus halei is the fourth species of the genus with 3-septate ascospores. Abrothallus bryoriarum Hafellner Reference Hafellner1994, A. suecicus (Kirschst.) Nordin Reference Nordin1964, and A. stictarum Etayo Reference Etayo2002 also have ascospores with three septa, however they differ from A. halei by having larger ascospores: (16–)17–20 × 6–8 µm in A. bryoriarum (Hafellner Reference Hafellner1994), 14–17(–20) × 5–7 µm in A. suecicus (Nordin Reference Nordin1964), and 13·5–18 × 5–6 µm in A. stictarum (Etayo Reference Etayo2002). Furthermore, A. bryoriarum grows on Bryoria species, A. suecicus on Ramalina species, and A. stictarum on Sticta species, and the ascospores are much less constricted at the central septum. Part-spores (semi-spores sensu Hawksworth Reference Hawksworth1990) occur in several 1-septate species of Abrothallus, namely in A. cladoniae R. Sant. & D. Hawksw. 1990, A. secedens Wedin & R. Sant. 1994, A. stereocaulorum Etayo & Diederich 2002, and in some undescribed species (A. Suija & S. Pérez-Ortega, personal observation). However, A. halei is the first species of the genus reported to have 4-celled ascospores which separate into two 2-celled part-spores.
Abrothallus halei represents the fifth species growing on members of the Peltigerales, Ascomycota. The other four species described so far differ from A. halei in ascospore sizes and septation, as well as in growing on different host genera. Abrothallus secedens occurs on species of Pseudocyphellaria and has 1-septate ascospores that easily split into two part-spores (Wedin Reference Wedin1994); A. granulatae on Pseudocyphellaria granulata has characteristic 2-septate ascospores (Wedin Reference Wedin1994); A. welwitschii (Tulasne Reference Tulasne1852) and A. stictarum, both on Sticta species have 1-septate and 1–3-septate ascospores, respectively (see above).
Dactylospora lobariella (Nyl.) Hafellner Reference Hafellner1979 (syn. Abrothallus lobariellus (Nyl.) Zopf 1896), another lichenicolous fungus with dark brown septate ascospores growing on Lobaria species, is readily distinguished from Abrothallus halei by several characteristics. The ascomata of D. lobariella measure (0·14–)0·2–0·6 mm diam., have a distinct and raised black exciple which contains blue-violet K+ green granules, a disc which is generally plane to concave and only convex with age, asci which have an I+ blue sheath, and ascospores which are consistently 1-septate, never break into part-spores, and measure 11–17 × 5–6 µm (Hawksworth Reference Hawksworth1975; Hafellner Reference Hafellner1979). Dactylospora lobariella is known from Africa (Canary Islands), Europe, and North America where the hosts include Lobaria pulmonaria, L. quercizans and L. virens.
We acknowledge the curators of the cited herbaria for granting the loan of specimens. Erich Kukk and Olev Nagel are thanked for their consultations on the species' name and Latin diagnosis. We would also like to express our special thanks to Rolf Santesson and Roland Moberg. The reviewers are thanked for their valuable comments. The study of AS was supported by Estonian Science Foundation grant no. GP1LM7321, target-financing project SF0180012s09 and the European Regional Development Fund (Centre of Excellence FIBIR). SPO is supported by the programme JAE-Doc (Consejo Superior de Investigaciones Científicas) and the projects CGL2007-66734-C03-01/BOS and CTM2009-12838-C04-03, and DLH by project CGL 2008-01600 (all from the Ministerio de Ciencia e Innovación, Spain).
