Introduction
The lichen family Graphidaceae has recently been rearranged, with new genera described, some older genera resurrected, and existing genera redefined (Staiger & Kalb Reference Staiger and Kalb1999; Staiger Reference Staiger2002; Kalb et al. Reference Kalb, Staiger and Elix2004; Lücking Reference Lücking2007; Lücking et al Reference Lücking, Chaves, Sipman, Umaña and Aptroot2008). As a result the family is now represented by 24 genera (Lücking Reference Lücking2009). Staiger (Reference Staiger2002) reintroduced the genus Hemithecium Trevis., which is distinguished by its well-developed, convergent labia, non-carbonized and often distinctly crenate exciple with internal striae, concealed disc and a puffy swollen lateral exciple that reacts reddish brown or brown in iodine.
The lichen genus Hemithecium is represented by 44 species worldwide, of which 24 species occur in India (Singh & Sinha Reference Singh and Sinha2010). Several new species and combinations of Hemithecium have been established based on material from India (Adawadkar & Makhija Reference Adawadkar and Makhija2005; Makhija & Adawadkar Reference Makhija and Adawadkar2005; Makhija et al. Reference Makhija, Dube, Adawadkar and Chitale2005; Tewari & Upreti Reference Tewari and Upreti2007; Chitale et al. Reference Chitale, Makhija and Sharma2009; Singh & Swarnalatha Reference Singh and Swarnalatha2009). While studying the lichens of West Siang district, Arunachal Pradesh in north-east India, an isidiate species of Hemithecium was found growing in association with Graphis scripta (L.) Ach., Sarcographa labyrinthica (Ach.) Müll. Arg., Phaeographis dentritica (Ach.) Müll. Arg. and pyrenocarpous lichens. It is described here as a new species. So far, the only other graphidacean species reported from India having isidiate thalli are Graphis patwardhanii Kulkarni and Graphis isidiza Adawadkar & Makhija (Kulkarni Reference Kulkarni1977; Adawadkar & Makhija Reference Adawadkar and Makhija2004).
Materials and Methods
Hand-cut sections of ascomata were mounted in water, 10% KOH solution, Lugol's iodine and lactophenol Cotton Blue (LB) and examined with a binocular Digizoom Stereo microscope and NIKON ECLIPSE E400. All the measurements were made on material mounted in water. The lichen substances were identified by thin-layer chromatography following Orange et al. (Reference Orange, James and White2001).
The New Species
Hemithecium isidiatum Upreti & U. Dubey sp. nov
MycoBank No.: 561209
Similis Hemithecium salacilabiatum praesentia acidum salazinicum sed differet isidiato thallo et ascosporis majoribus.
Typus: India, Arunachal Pradesh, West Siang district, Kago-kashi forest, near kabu village, Along, on bark, 20 March 2006, Urvashi Dubey 06-006525 (LWG—holotypus).
Hemithecium isidiatum. A, habit; B, coralloid isidia; C, vertical section of lirellae; D, ascospores. Scales: A = 1 mm, B = 0·5 mm, C = 20 µm, D = 5 µm.
(Fig. 1)
Thallus corticolous, crustose, epiperidermal, greenish grey to grey, sometimes greyish brown to pale brown, smooth and thick, isidia simple to coralloid branched, 0·2–0·4 mm diam. and 0·3–1·0 mm high, spread over the thallus, concolorous, easily detachable.
Apothecia lirellate, lirellae greyish white to grey, prominent, emergent, mostly simple, rarely branched, curved to flexuous, 1–4 mm long and 0·25–0·5 mm broad, ends obtuse, margin thick and covered by a thalline layer. Disc ± closed, slit-like, epruinose. Exciple non-carbonized, colourless to pale yellowish brown, basal region narrow and upper region wide with several striae; labia convergent entire, irregular on outer side, covered with thalline veil up to the top, crystals present above the exciple. Epihymenium dark brown, 6–9 µm high. Hymenium hyaline, not inspersed, 80–120 µm high. Hypothecium pale yellow to yellow, 14–18 µm high. Asci 4–8 spored, 45–77 long and 13–20 µm broad. Ascospores oblong-ellipsoid, hyaline, muriform, with 6–17 transverse septa and 1–5 longitudinal septa, 14–27(–35) × 6–8 µm, I+ blue.
Chemistry. Salazinic acid present in the thallus.
Etymology. The epithet is a reference to the presence of isidia, which are not known from other species of Hemithecium.
Ecology and distribution. The species is known from semi-evergreen forests, between altitudes of 250–500 m, West Siang District in Arunachal Pradesh, Eastern Himalayas. The new taxon grows mostly on smooth-barked trees in moist and humid places. Other species of lichens associated with the new species are Sarcographa labyrinthica (Ach.) Müll. Arg., Phaeographis dendritica (Ach.) Müll. Arg. and other members of the graphideon and pyrenocarpous lichens.
Remarks. In morphology of the lirellae and presence of isidia the new taxon may be confused with Platythecium dimorphodes (Nyl.) Staiger. However P. dimorphodes has 4-septate to submuriform small ascospores measuring 9–16 × 5–8 µm and the presence of norstictic and connorstictic acid in the thallus. The new taxon is distinguished from other species of the genus by having an isidiate thallus. In ascospore size and shape it is close to H. microspermum Chitale, Makhija & B. O. Sharma, but H. microspermum differs in having non-striate or weakly striate exciple and a different chemistry, having constictic, hyposalazinic, norstictic and stictic acids. Similar to the new taxon is H. salacilabiatum (Patw. & Kulk.) Chitale & Makhija, which also has salazinic acid but differs in having larger spores, measuring 130–200 × 35–60 µm, and in lacking isidia.
Additional specimens examined. India: Arunachal Pradesh: West Siang district, Kago-kashi forest, near kabu village, Along, on bark, 2006, Urvashi Dubey 06-006508, 06-006538, 06-006534 (LWG); Doji, 16 km from Along towards Basar, on bark, 2006, Urvashi Dubey 06-006391, 006361, 006376 (LWG).
The authors thank the Director of the National Botanical Research Institute, Lucknow for providing laboratory facilities and to the Ministry of Environment and Forest, New Delhi for financial support.
