Introduction
In November 2008, a team of Spanish lichenologists and Mexican and Spanish glaciologists began to study the Transmexican Volcanic Belt (TVB). It lies between 19°–21° N latitude, forming a nearly continuous belt from the Gulf of Mexico to the Pacific coast along fault systems oriented mainly along a WNW–ESE direction. It has been recognized as having distinct geological and biological features which make it a unique natural region.
This first lichenological expedition was centred in the Izta-Popocatepetl National Park, also known as Izta-Popo or PNIP. It was founded in 1935, but in 1948 the boundaries were expanded to include those regions above 3600 m, with a total area of 25·7 ha. PNIP is the southern part of the Mexican Sierra Nevada, and it is located just 60 km south of Mexico D.F. where the states Méjico, Puebla and Morelos meet. The geomorphological variety, climate and vegetation are responsible for the high plant diversity (more than 1000 species). Today the park is considered an important water resource and the old forests are making a good recovery.
Our goals included the study of the lichens and lichenicolous fungi of this region as well as lichenometric studies in the higher glaciers (Iztaccíhuatl, at 5240 m and Popocatepetl, at 5480 m). The present study is a contribution to the knowledge of this interesting, lichenologically unknown region.
Material and Methods
This study was based on herbarium material from the private herbaria of the second author (J. Etayo). The specimens were examined by standard techniques using stereoscopic and compound microscopes.
Only free ascospores lying outside the asci have been measured. Measurements were made in material mounted in water at ×1000 magnification. Mean value (M) and standard deviation (SD) were calculated and the results are given as (minimum value observed) M ± SD (maximum value observed). M, SD and n (the total number of ascospores measured) are given within parentheses. The terminology used for the proper excipulum- and ascospore-types follows Bungartz et al. (2007), for the asci Rambold et al. (Reference Rambold, Mayrhofer and Matzer1994) and for the ascospore ontogeny Giralt (Reference Giralt2001).
Chemical constituents were identified by high performance liquid chromatography (HPLC) (Elix et al. Reference Elix, Giralt and Wardlaw2003).
The Species
Buellia rhizocarpica Etayo, Giralt & Elix sp. nov
MycoBank No.: 516788
Buellia schaereri De Not similis sed in thallo acidum rhizocarpicum et pulvinicum continens; hymenium flavum quia crystalles K+ rosei et ascosporae maiores (9–)10–12(–14) × (3–)3–4·5(–6) µm.
Typus: Mexico, from Refugio de Pocatépetl to repetidor, on old Pinus hartwegii, 3950 m, 19°03′39″N, 98°37′57″W, 2 November 2008, J. Etayo (MEXU—holotypus; BCN, hb. Etayo 24882—isotypi).
(Fig. 1)
Fig. 1: Buellia rhizocarpica (holotype). A, habitus; B, ascospores; C & D, hymenium with asci, paraphyses and crystal clusters (arrows). Scales: A = 100 µm; B, C & D = 10 µm.
Thallus epiphloeodic, ±continuous, covering wide areas, indeterminate, yellowish green, yellowish orange or yellowish grey; composed of granules 0·1–0·5 mm diam. (Fig. 1A) covered by a gelatinous, hyaline cortex intermixed with dead algal cells. Alga chlorococcoid, 10–15(–18) µm diam. with oil droplets, intermixed with hyphae and many small yellow crystals soluble in K. Medulla I−.
Apothecia lecideine, adnate or rarely sessile, black, (0·2–)0·3–0·4(–0·5) mm diam., abundant, confluent. Proper margin thin, usually persistent. Disc plane to subconvex or rarely convex, epruinose (Fig. 1A). Proper excipulum aethalea-type, blackish green (micromera-green), N+ blackish, K+ yellowish green, KC+ dark blue-green to blackish. Hymenium hyaline, 60–80 µm high, with many small yellow crystals forming clusters (Fig. 1C & D) which dissolve in K to give a pinkish solution; epihymenium dark brown to olivaceous black (micromera-green). Hypothecium 150 µm deep, dark brown, upper part aeruginose (micromera-green). Paraphyses very thin, up to 1 µm wide; apical cells capitate, 2–4 µm wide, olivaceous. Asci 8-spored, Bacidia-type. Ascospores pale brown, Buellia-type, (9–)10–12(–14) × (3–)3·5–4·5(–6) µm [M =11·1; 4·1 µm; SD 1·1; 0·5 µm; n = 70], walls very thin, smooth at ×1000, ontogeny of type A (Fig. 1B & D).
Conidia short bacilliform to almost globose, 2–4·5 × 1·5–2 µm.
Chemistry. Thallus K+ purple; C+ rose, KC+ pale purple, Pd−, UV+ dark orange. Atranorin [minor], rhizocarpic acid [major], epanorin [minor], conrhizocarpic acid [minor], gyrophoric acid [minor], alectorialic acid [minor], unknown pulvinic acid derivative [major].
Ecology and distribution. At present B. rhizocarpica is known only from the type locality, at the base of the volcano Popocatepetl in Central Mexico where it grows on the bark of Pinus hartwegii Lindl. in a well-preserved P. hartwegii forest with a rich epiphytic lichen flora. Accompanying species included several large foliose thalli of Hypogymnia bitteri (Lynge) Ahti, Pseudevernia consocians (Vain.) Hale & W. Culb, P. intensa (Nyl.) Hale & W. Culb., Punctelia aff. subrudecta (Nyl.) Krog and Tuchermannopsis platiphylla (Tuck.) Hale. Other crustose lichens associated with B. rhizocarpica included Candelariella aff. efflorescens R. C. Harris & Buck, Cyphelium tigillare (Ach.) Ach., Ochrolechia cf. parella (L.) A. Massal., Pertusaria sp., Pycnora xanthococca (Sommerf.) Hafellner, Pyrrhospora sp. and Scoliciosporum chlorococcum (Graewe ex Stenh.) Vězda.
Observations. Buellia rhizocarpica is characterized by its granulose, yellowish thallus containing rhizocarpic acid and an unknown pulvinic acid derivative as major secondary metabolites, apothecia containing the pigment micromera-green in the proper excipulum, epihymenium and hypothecium, a hymenium interspersed with abundant, small yellow crystals which react K+ pinkish and by small Buellia-type ascospores, with pale, thin, smooth walls.
Among all the Buellia s. lat. species hitherto described only B. schaereri De Not. has such small ascospores. However, B. schaereri has a thin, greyish to inconspicuous thallus without secondary metabolites or containing only atranorin (Marbach Reference Marbach2000, sub. Amandinea endachroa (Malme) Reference Bungartz, Nordin, Grube, Nash, Ryan, Diederich, Gries and BungartzMarbach; Bungartz et al. Reference Bungartz, Nordin, Grube, Nash, Ryan, Diederich, Gries and Bungartz2007), smaller apothecia (up to 0·2–0·3 mm diam.), significantly smaller ascospores (M: 8·4 × 3·9 µm), a hymenium without crystals, and a brown to brown-olivaceous proper excipulum, epihymenium and hypothecium containing low concentrations of the micromera-green pigment.
According to Obermayer et al. (Reference Obermayer, Blaha and Mayrhofer2004), rhizocarpic acid is known in the Physciaceae only from Dermatiscum thunbergii (Ach.) Nyl. and Buellia centralis H. Magn. As rhizocarpic acid was only known from one species of Buellia s. lat., we considered the possibility that B. rhizocarpica could be parasitic on a yellow epiphytic lichen thallus. The thalline granules of B. rhizocarpica resemble those of some species of Candelariella Müll. Arg., a genus known to contain pulvinic acid and calycin, but which lacks rhizocarpic acid (Geyer Reference Geyer1985). Another chemically similar, yellow genus is Chrysothrix Mont. It normally contains pulvinic acid derivatives and some species produce rhizocarpic acid, including C. chrysophthalma (P. James) P. James & J. R. Laundon and C. flavovirens Tønsberg. However, the thalli of these two species are clearly different, with the former being entirely immersed (endophloeodic) and the second uniformly sorediate, with soredia up to 0·02–0·025 mm diam. (Tønsberg Reference Tønsberg1994; Fletcher & Purvis Reference Flechter, Purvis, Smith, Aptroot, Coppins, Fletcher, Gilbert, James and Wolseley2009).
A further important reason for considering that the yellowish thallus actually belongs to B. rhizocarpica rather than to a host thallus, is the fact that the crystals which form clusters within the thallus are also present in large quantities in the hymenium, intermixed with the paraphyses.
The first author thanks L. G. Sancho, friends of UAM led by J. J. Zambrano and the ANTEX project for the opportunity to collect in the Transmexican Volcanic Belt. The second author is grateful for funding of the project CGL2007-66734-C03-02/BOS from the Spanish Government. We thank Fernando Abascal (IES Zizur Mayor) for assistance with the Latin diagnosis.
