Introduction
The lichenicolous genus Plectocarpon Fée (Roccellaceae, Arthoniales) is characterized by multilocular stromata, usually inducing gall-like structures on the host thalli, Opegrapha-like asci surrounded by branched and anastomosing paraphyses, and usually 3-septate, rarely 1 or (4–)5–6(–7)-septate ascospores, which sometimes become brown at maturity. It consists of 34 species parasitizing various lichen genera, mainly belonging to the Peltigerales, but also members of Cladoniaceae, Ramalinaceae, Parmeliaceae and Sphaerophoraceae in the Lecanorales (Diederich & Etayo Reference Diederich and Etayo1994; Ertz et al. Reference Ertz, Christnach, Wedin and Diederich2005; Etayo Reference Etayo2007; Etayo & Sancho Reference Etayo and Sancho2008; Zhurbenko et al. Reference Zhurbenko, Diederich and Otnyukova2008). In this paper we describe the first species parasitizing Stereocaulon.
Material and Methods
The morphology and anatomy were examined using NIKON SMZ800 and NIKON ECLIPSE 80i (DIC) microscopes. The anatomy was studied on material mounted in water, KOH solution (K), and for ascus structure Lugol's iodine solution without (I) or with pre-treatment with KOH (K/I). The measurements of ascospores were made in water and K, all other measurements only in water.
The New Species
Plectocarpon stereocaulicola Kukwa, Etayo & Flakus sp. nov.
MycoBank No.: MB 564554
Species superficially similar to Plectocarpon latisporum (on Pseudocyphellaria coriifolia), which also forms galls with a thalline pseudo-margin, but differs in ascomata with a non-carbonized, light brown sterile stromatic tissue in the lower part, larger ascospores 20–28(–30)×6·5–8·0 µm and a different host (Stereocaulon sp.).
Typus: Bolivia, Dept. La Paz, Prov. Nor Yungas, below Unduavi village, near Rio Unduavi, 16°18′50″S, 67°54′35″W, 3135 m, Yungas cloud forest, on thallus of saxicolous Stereocaulon, A. Flakus 22222, J. Etayo & O. Plata (KRAM—holotypus; LPB, UGDA, hb. Etayo—isotypi).
(Fig. 1A–G)
Plectocarpon stereocaulicola (holotype). A & B, habit of the fungus inducing galls with thalline pseudo-margin; C, carbonized, rough and cracked surface of stroma; D, section through multilocular stroma; E, fertile loculus; F, asci with young (left) and mature, brown ascospores with a granular-rugose surface (right); G, young, hyaline ascospores with gelatine epispore (left), and mature, brown ascospores with a granular-rugose epispore (right). Scales: A & C=1 mm; B=0·5 mm; D=250 µm; E=50 µm; F=25 µm; G=10 µm. In colour online.
Ascomata developing apically on pseudopodetia or pseudopodetial branches, sometimes directly on the surface of pseudopodetia (then usually shortly stipitate), single or rarely confluent, black, rounded, flattened to convex, inducing the formation of galls with constricted base and thin to thick thalline pseudo-margin, surface rough, cracked and epruinose, 0·3–2·0(–2·5) mm diam. Stroma multilocular, with carbonized surface, sterile stromatic tissue developed between fertile loculi prosoplechtenchymatic, not carbonized, pale brown, K+ olive-brownish, N+ reddish brown or N−, 20–25 µm in lateral, 25–75 µm in basal zones, without immersed crystals, but in upper part distinctly carbonized, dark orange-brown to blackish; pigment not dissolving, granular (better seen in K), K+ olive-brown (with slightly greyish green appearance when in lower concentration), N+ reddish brown (Atra-brown; Meyer & Printzen Reference Meyer and Printzen2000). Hymenium hyaline, 100–150 µm high, fertile loculi c. 150–260 µm diam.; hymenial gel I+ blue, K/I+ blue. Paraphyses abundant, richly branched and sometimes anastomosed, septate, 1·5–3·0 µm thick, apically not distinctly enlarged and not darker. Asci clavate, (6–)8-spored, 65–85(–115)×15–20 µm, Opegrapha-type, with only apical ring K/I+ blue. Ascospores hyaline, smooth, thick-walled when young, becoming brown when mature and with a distinct granular-rugose epispore, 3-septate, slightly constricted at the septa, all cells are more or less equal in length, 20–28(–30)×6·5–8·0 µm in water, 20–28(–30)×(6·5–)7·0–9·0 µm in K, length/breadth ratio (2·5–)3·0–3·6 (n=20), gelatine perispore distinct (especially in young ascospores), hyaline, up to 2 µm thick (better seen in K).
Pycnidia intermixed with the ascomatal loculi in the same stroma, very small, c. 40–50 µm diam., with hyaline wall; conidiogenous cells elongate cylindrical, 7–10×1·5–2·0 µm; microconidia bacilliform, hyaline, simple, 3–5×1 µm.
Host. The species inhabits saxicolous thalli of an unidentified sorediate Stereocaulon sp. It causes galls surrounded by a thalline border on the host thallus; no other damage to the host thallus was visible. Remarkably, we have found this new fungus only on this particular sorediate Stereocaulon species, and not on other more frequent taxa occurring in the same localities.
Distribution and habitat. The new species is known from two Bolivian localities. It has been found in the Paramo Yungeño open vegetation and Yungas cloud forest.
Notes. Plectocarpon latisporum Ertz et al., which also forms galls with a thalline pseudo-margin and finally brown granulose ascospores, is the most similar species to P. stereocaulicola. However, it can be distinguished by its dark brown to black stromatic tissue below fertile loculi, comparatively shorter ascospores (17·0–)19·0–22·8(–25·0)×(5·5–)6·2–7·6(–8·0) µm, and unrelated foliose Pseudocyphellaria coriifolia as a host (Ertz et al. Reference Ertz, Christnach, Wedin and Diederich2005).
Plectocarpon pseudosticta Fée, another species growing on Pseudocyphellaria, also shows some similarities in gall formation, but has dark brown to black stromatic tissue below loculi and smaller, (16·0–)18·2–22·7(–24·0)×(4·8–)5·2–5·9(–6·0) µm, ascospores with a larger (3·3–4·1) length/breadth ratio (Ertz et al. Reference Ertz, Christnach, Wedin and Diederich2005).
The new species also superficially resembles P. cladoniae R. Sant and P. usneaustralis Etayo, owing to the round, black, rough and warted ascomata with carbonized upper part and induction of galls with a thalline pseudo-margin (Ertz et al. Reference Ertz, Christnach, Wedin and Diederich2005; Etayo Reference Etayo2007). However, both species can easily be distinguished by the dark brown (P. cladoniae) or carbonized (P. usneaustralis) lower part of sterile stromatic tissue and different hosts, Cladonia and Usnea respectively. Additionally P. cladoniae has (4–)5-septate ascospores and P. usneaustralis develops comparatively smaller ascomata, 0·4–0·7(–1·3) µm diam. (Ertz et al. Reference Ertz, Christnach, Wedin and Diederich2005; Etayo Reference Etayo2007).
By its 3-septate ascospores and non-carbonized sterile stromatic tissue in the lower part, P. stereocaulicola is also similar to P. cristalliferum Christnach et al. and P. scrobiculatae Diederich & Etayo. However, both of these have a non-carbonized surface of stromata. Furthermore, P. cristalliferum does not induce gall formation, the discs of ascomata have whitish points due to immersed crystals, ascospores are smaller, 15–21×3·5–4·5 µm (Ertz et al. Reference Ertz, Christnach, Wedin and Diederich2005), and it inhabits thalli of Sticta. Plectocarpon scrobiculatae parasitizes Lobaria scrobiculata and has similarly sized ascospores, but they are never brown when mature, and the ascomata are reddish brown (pigment K−, N−), with radially arranged loculi (Diederich & Etayo Reference Diederich and Etayo1994).
Opegrapha stereocaulicola Alstrup & D. Hawksw. is the only other member of the family Roccellaceae that grows on Stereocaulon species. It differs from Plectocarpon stereocaulicola by its elongate, lirelliform, non-stromatic ascomata, an exciple that is carbonized even below the hymenium, brownish distal cells of paraphyses and smaller asci (50–65 µm long); ascospores are also 3-septate (rarely with up to 5 septa), but smaller and measure 19–21×5–6 µm (Alstrup & Hawksworth Reference Alstrup and Hawksworth1990).
Additional specimens examined (both on Stereocaulon sp.). Bolivia: Dept. La Paz: Prov. Nor Yungas, near Pongo village, 16°19′28″S, 67°57′21″W, 3822 m, Paramo Yungeño vegetation, 2011, M. Kukwa 9395 (LPB, UGDA); ibid., 2011, A. Flakus 22925 & M. Kukwa 10110 (BR, LPB, UGDA, hb. Flakus).
We are greatly indebted to Paul Diederich (Luxembourg) and an anonymous reviewer for very helpful comments, and to Rosa I. Meneses Q., the Director of Herbario Nacional de Bolivia, Instituto de Ecología, Universidad Mayor de San Andrés, La Paz, for generous cooperation. We also thank U. Schiefelbein (Rostock) and O. Plata (La Paz) for valuable help during fieldwork. This research received support from the National Centre for Research and Development (NCBiR) in Poland under the LIDER Programme for the years 2010–2013 (no. 92/L–1/09).
