Introduction
The lichen genus Leiorreuma Eschw. (Graphidaceae) is represented by 19 species world-wide of which Leiorreuma exaltatum (Mont. & Bosch) Staiger and L. melanostalazans (Leight.) A. W. Archer, are found in India (Archer Reference Archer2006). The genus is characterized by an off-white to pale olive-green thallus with a smooth to dull surface; lirellate, conspicuous, sessile apothecia with epruinose to weakly pruinose discs, a poorly to well-developed exciple, an inspersed hymenium; pale brown, elongate, ellipsoid and I+ red-brown ascospores, with or without secondary metabolites. During the course of lichenological studies in the Upper Siang district of Arunachal Pradesh, eastern India, a number of graphidaceous lichens were collected and among them a new species of Leiorreuma was found which is described here.
Materials and Methods
Morphological characters were examined on dry material under a stereo-zoom microscope and anatomical details were examined with a compound microscope. The hand-cut sections of lirellae and thallus were mounted in water, 10% KOH (K), Lugol's solution (I) and cotton blue. All the measurements were made on material mounted in water. Secondary metabolites were sought by TLC (Orange et al. Reference Orange, James and White2001)
The New Species
Leiorreuma subpatellulum Dubey, Upreti & Nayaka sp. nov
MycoBank No.: 518121
Thallus crustaceus, corticola, ascomata lirellata (0·5–3·0 × 0·3–0·5 mm) vel rotundata (0·25–1·0 × 0·3–0·5 mm), primum immerse deinde adnata, discus pruinosus. Excipulum nigrum, hymenium inspersum, asci claviformes, 4–8 spori, 60–70 × 15–18 µm, ascosporae fusiformes, 40–46 × 8–10 µm, 6–12 septatae, brunneae.
Typus: India, Arunachal Pradesh, Upper Siang District, Jengging, near circuit house, 28º 54′ N 95º 06′ E, 900 m, on bark, 30 October 2007, U. Dubey 07-011897 (LWG—holotypus).
(Fig. 1 A–D)
Leiorreuma patellulum. A, habit (holotype); B, cross section of ascomata; C, ascus; D, ascospores. Scales: A = 5mm; B = 20 µm; C & D = 10 µm.
Thallus corticolous, crustose, olive-green to yellow-brown or pale brown, smooth, ecorticate.
Ascomata numerous, crowded, rounded (0·25–1·0 × 0·3–0·5 mm) to lirellate (0·5–3·0 × 0·3–0·5 mm), immersed to adnate, simple to branched. Disc broad, pruinose, plane. Margin persistent, covered densely with white pruina, up to 75 µm thick, with crystals, Pd−. Exciple well developed, completely carbonized, convergent, K−, 25–50 µm thick. Hymenium hyaline, 80–130 µm thick, inspersed with oil, I+ reddish brown. Subhymenium pale brown to dark brown, 20–30 µm thick. Paraphyses up to 2·0 µm thick, branched and anastomosing, not widened at the apices. Asci cyclindrico-clavate, 4–8 spored, 60–70 × 15–18 µm. Ascospores hyaline when young, pale brown at maturity, oblong, ellipsoid, 6–12 transversely septate, 40–46 × 8–10(–12) µm, one end tapering with locules in the centre larger, irregular in shape, I+ reddish brown.
Pycnidia not seen.
Chemistry. Thallus K+ red, KC+ yellow turning red, Pd−; no lichen substances detected by TLC in solvent system A.
Etymology. The epithet subpatellulum is a reference to the similarity of the new species with Leiorreuma patellulum (Fée) Staiger.
Ecology and distribution. The species is so far known only from its type locality in the Jengging area in the Upper Siang District of Arunachal Pradesh where it grows in moist, humid conditions in association with Sarcographa labyrinthica (Ach.) Müll. Arg., and other members of the Graphidaceae.
Remarks. The new taxon is characterized by rounded to lirellate ascomata, 6–12-septate, 40–46 × 8–10 µm ascospores with one end tapering. The well-developed exciple is similar to that in L. patellulum, but the latter species has larger ascospores measuring 60–80 × 7–8 µm, 12–18 locular ascospores and in addition contains norstictic acid. Leiorreuma patellulum is distributed in South America.
The two other Indian species L. exaltatum and L. melanostalazans differ in having poorly developed exciples, immersed lirellae and smaller 4–6 locular (20–30 × 7–9 µm) and 7–9-locular (25–37 × 8–10 µm) ascospores respectively. The other species of Leiorreuma, L. nornotaticum (A. W. Archer & Elix) A. W. Archer, L. dilatatum (Vain.) Staiger L. sericeum (Eschw.) Staiger L. ellipticum (Müll. Arg.) Staiger and L. lyellii (Sm.) Staiger all differ in having poorly developed exciples.
In its morphology and well-developed proper exciple the new taxon is close to the other graphidaceous lichen genera, Thecographa and Thecaria. However, Thecaria differs in having a proper exciple covered by a thalline layer up to the top whereas Thecographa has completely naked lirellae. In L. subpatellulum, the thalline layer covers only the lateral side of the exciple leaving the top portion completely naked. Such a condition is also observed in L. patellulum. Further, in Thecaria the disc is usually sunken and all the species reported so far have muriform ascospores.
The species of Phaeographis, another graphidaceous genus, can be confused with the new species in the shape and size of the lirellae. However, most species of Phaeographis can be distinguished by a poorly developed exciple. Phaeographis fusca Staiger, P. lepreiurii (Mont.) Staiger and P. patagonia Zahlbr. all have a well-developed exciple similar to that in the new taxon. Phaeographis fusca differs in having muriform spores whereas P. patagonica is characterized by 6-locular ascospores measuring 20–30 × 6–9 µm and a poorly developed exciple on lateral sides. Phaeographis lepreiurii can be distinguished by having a non-carbonized exciple at the base, 6-locular ascospores measuring 17–25 (–30) × 6–9 µm and a non-inspersed hymenium. Phaeographis lobata (Eschw.) Müll. Arg. resembles the new species in shape, size and colour of ascospores but differs in having exciples carbonized only at the apices and oval shaped lirellae.
Platygramme reticulata (Fée) Fée resembles the new taxon in having a carbonized excipular base, similar chemistry and a well-developed exciple, but it differs by the wedge-shaped apices and muriform spores.
