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Wirthiotrema: a new genus for the Thelotrema glaucopallens group (Ascomycota: Ostropales: thelotremoid Graphidaceae)

Published online by Cambridge University Press:  29 January 2010

Eimy RIVAS PLATA ,
Klaus KALB  and
Andreas FRISCH
Eimy RIVAS PLATA
Affiliation:
Department of Botany, The Field Museum. 1440 S Lake Shore Drive, Chicago IL 60605, USA. Email: erivasplata@fieldmuseum.org; Biological Sciences Department, University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607, USA.
Klaus KALB
Affiliation:
Lichenologisches Institut Neumarkt, Im Tal 12, D-92318 Neumarkt, Germany.
Andreas FRISCH
Affiliation:
Department of Ecology, Swedish University of Agricultural Sciences, P.O. Box 7044 SE 750 07 Uppsala, Sweden.
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Abstract

The new genus Wirthiotrema Rivas Plata, Kalb & Frisch. is described for the Thelotrema glaucopallens group, based on molecular and morphological evidence, with W. glaucopallens as the type species. The genus is characterized by myriotremoid thalli and apothecia, in combination with a paraplectenchymatous excipulum, I− ascospores, and stictic acid as a secondary compound. The new combinations W. glaucopallens (Nyl.) Rivas Plata & Kalb comb. nov., W. santessonii (Hale) Rivas Plata & Frisch comb. nov., and W. trypaneoides (Nyl.) Rivas Plata & Lücking comb. nov., are proposed and a key to the three species is presented.

Keywords

Ostropalean fungiLeptotremaLeucodectonThelotremataceae
Type
Research Article
Information
The Lichenologist , Volume 42 , Issue 2 , March 2010 , pp. 197 - 202
Copyright
Copyright © British Lichen Society 2010

Introduction

Ostropalean fungi include the Graphidaceae and Thelotremataceae (Eriksson & Hawksworth Reference Eriksson and Hawksworth1998; Winka et al. Reference Winka, Ahlberg and Eriksson1998; Lutzoni et al. Reference Lutzoni, Pagel and Reeb2001; Kauff & Lutzoni Reference Kauff and Lutzoni2002), both important components of tropical lichen communities. The two families were recently revised (Staiger Reference Staiger2002; Frisch et al. Reference Frisch, Kalb and Grube2006), and Mangold et al. (Reference Mangold, Martìn, Kalb, Lücking and Lumbsch2008a) demonstrated polyphyly among them, resulting in the inclusion of Thelotremataceae in Graphidaceae. Genera in the former Thelotremataceae were traditionally separated by ascospore characters (Redinger Reference Redinger1936; Salisbury Reference Salisbury1972a,Reference Salisburyb; Hale Reference Hale1973, Reference Hale1974, Reference Hale1978) into Ocellularia (transversely septate, hyaline), Phaeotrema (transversely septate, brown), Thelotrema (muriform, hyaline) and Leptotrema (muriform, brown), or by excipular characters (Salisbury Reference Salisbury1971, Reference Salisbury1972a,Reference Salisburyb, Reference Salisbury1978; Hale Reference Hale1980, Reference Hale1981) into Thelotrema (uncarbonized with lateral paraphyses), Myriotrema (non-carbonized, lacking lateral paraphyses), and Ocellularia (carbonized, lacking lateral paraphyses). Kalb (Reference Kalb2004) and Frisch et al. (Reference Frisch, Kalb and Grube2006) used a combination of thallus, apothecial, ascospore, and chemical characters to distinguish 21 genera, among them the reinstated Chapsa, Leucodecton and Stegobolus and the newly established Acanthotrema, Ampliotrema, Fibrillithecis, Gyrotrema, Melanotrema, Redingeria, and Reimnitzia. Further contributions added two further genera, Melanotopelia and Schizotrema (Mangold et al. Reference Mangold, Martìn, Lücking and Lumbsch2008b; Mangold et al. Reference Mangold, Elix and Lumbsch2009), but some of the distinctive species groups in the family have not yet been formally redispositioned and remain in the collective genera Myriotrema, Ocellularia and Thelotrema, respectively.

Thelotrema traditionally comprised species with muriform, hyaline ascospores. Based on Salisbury (Reference Salisbury1971, Reference Salisbury1972a,Reference Salisburyb, Reference Salisbury1978), Hale (Reference Hale1980) changed the generic concept to include species with a non-carbonized excipulum and lateral paraphyses. Frisch et al. (Reference Frisch, Kalb and Grube2006) provided a narrower concept, restricting the genus to species with a non-carbonized, paraplectenchymatous excipulum, lateral paraphyses, lepadinoid apothecia with a more or less entire thalline margin and free proper excipulum (double margin), a thallus usually with a weakly developed or without a cortex, and stictic acid and related substances as dominant secondary compounds. Myriotrema, on the other hand, was defined by lack of lateral paraphyses, prosoplectenchymatous, usually fused excipulum, a thallus with a usually prosoplectenchymatous and often split cortex, and frequently psoromic acid as a secondary substance. A third genus, Leucodecton, is intermediate between Thelotrema and Myriotrema in lacking lateral paraphyses but having a paraplectenchymatous excipulum, a weakly developed or absent thallus cortex, and stictic acid as dominant secondary substance. Frisch et al. (Reference Frisch, Kalb and Grube2006) identified two closely related species variously placed in either Thelotrema or Myriotrema, viz. T. glaucopallens and T. santessonii, that did not fit in any of the three genera and also in the molecular phylogenetic analysis fell outside these clades (Frisch et al. Reference Frisch, Kalb and Grube2006; Mangold et al. Reference Mangold, Martìn, Kalb, Lücking and Lumbsch2008a). The so-called Thelotrema glaucopallens group was found to be most similar to Leucodecton but differed particularly in the Myriotrema-type, prosoplectenchymatous cortex with internal splitting. Molecular analysis by Mangold et al. (Reference Mangold, Martìn, Kalb, Lücking and Lumbsch2008a) also showed Myriotrema trypaneoides as a sister species of T. glaucopallens, and examination of the morphological characters confirmed that the species shares the paraplectenchymatic excipulum, I− ascospores, and presence of stictic acid as a secondary compound with T. glaucopallens and T. santessonii. Because of the morphological differences and its isolated phylogenetic position, we describe the new genus Wirthiotrema for this group of species.

The new genus

Wirthiotrema Rivas Plata, Kalb, Frisch & Lumbsch gen. nov

Mycobank no. MB 512786

Genus novum ad familiam Graphidacearum pertinens. Leucodecto similis sed cortice thallino prosoplectenchymatico et ascosporis hyalinis I– differt.

Type species: Wirthiotrema glaucopallens (Nyl.) Rivas Plata & Kalb

(Figs 1 & 2)

Fig. 1. Wirthiotrema glaucopallens. A–E, thallus with apothecia; F, ascospore. [A, holotype; B, isotype; C, Costa Rica, Lücking 17064(F); D, Costa Rica, Lücking 15620 (F); E, Costa Rica Sipman 37294 (B); F; holotype]. Scales: A–E = 1 mm, F = 10 μm.

Fig. 2. Wirthiotrema species. A–C, W. trypaneoides; A & B, thallus with apothecia; C, ascospore [A, Costa Rica, Sipman 37286 (B); B, Costa Rica, Lücking 1563 (F); C, lectotype].; D–F, W. santessonii (holotype); D, thallus with apothecia; E & F, dactyls. Scales: A, B, D–F = 1 mm; C = 10 μm.

Thallus corticolous, yellow-green to light olive, smooth to uneven-rimose and often fissured, up to 250 μm thick. Cortex well-developed, prosoplectenchymatous, compact and strongly conglutinated, partially with internal splitting, 5–20 μm thick. Dactyls (‘pustules’) present in one species.

Apothecia myriotremoid, immersed to erumpent, round, up to 0·6 mm diam. with a pore up to 0·2 mm wide; disc immersed, hardly visible, brown-black with a thin white pruina; thallus margin concolorous with the thallus. Excipulum fused (to rarely partially free), paraplectenchymatous, laterally pale brown but apically darker, up to 50 μm broad; periderm layer usually distinct, up to 30 μm broad. Lateral paraphyses absent. Hypothecium pale, up to 10 μm high. Epithecium grey-brown, granular, K−. Hymenium 80–170 μm high, clear; columella and columelloid structures absent; paraphyses simple, straight, 1·5–2 μm thick, with slightly thickened apices. Asci of the Thelotrema type, clavate, 90–160 × 10–25 μm. Ascospores 8 per ascus, ellipsoid, muriform with 5–9 transverse and 1–3 longitudinal septa per segment, 20–50 ×9–15 μm, distoseptate, hyaline or brown, I−.

Pycnidia immersed to erumpent, 0·4–0·8 mm diam. with 1–4, white to brownish pores, 0·1–0·4 mm wide. Wall prosoplectenchymatous, hyaline to pale brown, apically dark brown, laterally 10–20 μm wide but up to 120 μm apically. Conidiophores of Vobis type II(–IV). Conidiogeneous cells bottle-shaped, 7–11 × 1·5–2 μm. Conidia formed acrogenously, oblong to fusiform, 2·5–3·5 × 1–1·2 μm.

Secondary chemistry. Stictic acid and satellite substances (acetylconstictic acid, constictic acid, consalazinic acid and others).

Etymology. We dedicate this new genus to Prof. Dr Volkmar Wirth for his numerous outstanding contributions to lichenology.

Distribution and ecology. Pantropical; in lowland to lower montane rainforests, on bark of tree trunks in shady to semi-exposed conditions.

Remarks. The genus Wirthiotrema is characterized by its myriotremoid thallus with a prosoplectenchymatous, partially split cortex, its immersed to erumpent, myriotremoid apothecia with a more or less fused, paraplectenchymatous, brownish excipulum, its muriform, hyaline or brown, non-amyloid ascospores, and stictic acid as a major secondary substance. The genus is externally most similar to Myriotrema but differs in the paraplectenchymatous excipulum and the non-amyloid ascospores. These characters are reminiscent of Thelotrema, but that genus has a thallus with a weakly developed to absent cortex and lepadinoid apothecia with double margin and lateral paraphyses. Apothecial structure, thallus chemistry, and the cell arrangement of the ascospores are reminiscent of Leucodecton, but Wirthiotrema differs from that genus in the prosoplectenchymatous thallus cortex with internal splitting and the hyaline, non-amyloid ascospores lacking ornamentation. Furthermore, molecular analyses (Frisch et al. Reference Frisch, Kalb and Grube2006; Mangold et al. Reference Mangold, Martìn, Kalb, Lücking and Lumbsch2008a) placed Wirthiotrema distant from Leucodecton.

Wirthiotrema thus far contains three species:

Wirthiotrema glaucopallens (Nyl.) Rivas Plata & Kalb comb. nov

Mycobank no. MB 512787

Thelotrema glaucopallens Nyl., Ann. Sci. Nat., Bot., Sér. 4, 19: 327 (1863).

Wirthiotrema santessonii (Hale) Rivas Plata & Frisch comb. nov

Mycobank no. MB 512788

Thelotrema santessonii Hale, Phytologia 26: 417 (Reference Poelt1973).—Myriotrema santessonii (Hale) Hale, Mycotaxon 11: 135 (1980).

Wirthiotrema trypaneoides (Nyl.) Rivas Plata & Lücking comb. nov

Mycobank no. MB 512789

Thelotrema trypaneoides Nyl., Ann. Sci. Nat. Bot. sér. 4, 19: 335 (1863).—Leptotrema trypaneoides (Nyl.) Riddle, Bull. Torrey Bot. Cl. 43: 151 (1916).—Myriotrema trypaneoides (Nyl.) Hale, Mycotaxon 11: 135 (Reference Hale1980); type: Cuba, Wright 156 (FH-Tuck.—lectotype selected by Hale [1978: 54]; US!—isolectotype).

Thelotrema subterebrans Nyl., Flora 59: 561 (1876) [fide Hale Reference Hale1978].—Leptotrema subterebrans (Nyl.) Zahlbr., Cat. Lich. Univ. 2: 640 (1923); type: Cuba, Wright 520 (H, hb. Nylander 22514—lectotype)

Thelotrema laevius Vain., Journ. of Bot. 34: 207 (1896).—Leptotrema laevius (Vain.) Zahlbr., Cat. Lich. Univ. 2: 635 (1923); type: St. Vincent, Elliott s. n. (TUR-Vain. 26774!—lectotype).

(Fig. 2)

Key to Wirthiotrema species

  1. 1 Hymenium inspersed; ascospores brown ... W. trypaneoides

    Hymenium clear ... 2

  2. 2(1) Dactyls present ... W. santessonii

    Dactyls absent ... W. glaucopallens

Wirthiotrema glaucopallens and W. santessoniiare closely related and agree in thallus and apothecial features and chemistry but differ in the presence of conspicuous dactyls in Wirthiotrema santessonii. They form a species pair as defined by Poelt (Reference Poelt1970, Reference Poelt1972). Wirthiotrema glaucopallens somewhat resembles Ocellularia clandestina (Frisch et al. Reference Frisch, Kalb and Grube2006), but the latter has a whitish thallus owing to a strong incrustation with calcium oxalate crystals, apothecia with an apically carbonized excipulum and columella, and ascospores with trypethelioid walls and septa. The dactyls (‘pustules’) of W. santessonii are unique among Graphidaceae and show a great variability with respect to coarseness and size. Their apex often breaks open and exposes the central cavity. Soredia are not formed, but small thallus fragments removed from the apex might function as diaspores, a phenomenon also known from species in Pyxine (Kalb Reference Kalb1987), and similar to the schizidia of Stegobolus (Frisch et al. Reference Frisch, Kalb and Grube2006). According to Frisch et al. (Reference Frisch, Kalb and Grube2006), open dactyls may also play a role in gas exchange and their enlarged surface could be advantageous for photosynthesis in the rather shady habitat in which this species is usually found.

This study was made possible by two grants provided by the United States National Science Foundation (NSF): “TICOLICHEN” (DEB 0206125; PI Lücking); and “Phylogeny and Taxonomy of Ostropalean Fungi” (DEB 0516116; PI Lumbsch, Co-PI Lücking).

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Figure 0

Fig. 1. Wirthiotrema glaucopallens. A–E, thallus with apothecia; F, ascospore. [A, holotype; B, isotype; C, Costa Rica, Lücking 17064(F); D, Costa Rica, Lücking 15620 (F); E, Costa Rica Sipman 37294 (B); F; holotype]. Scales: A–E = 1 mm, F = 10 μm.

Figure 1

Fig. 2. Wirthiotrema species. A–C, W. trypaneoides; A & B, thallus with apothecia; C, ascospore [A, Costa Rica, Sipman 37286 (B); B, Costa Rica, Lücking 1563 (F); C, lectotype].; D–F, W. santessonii (holotype); D, thallus with apothecia; E & F, dactyls. Scales: A, B, D–F = 1 mm; C = 10 μm.