During recent lichen surveys in Chu Yang Sin, Phong Nha Ke Bang and Bach Ma National Parks, Vietnam, one of the authors (TTN.) had the opportunity to study foliicolous lichens and documented c. 50 foliicolous lichen species (T. T. Nguyen, unpublished data), of which 14 are new to the Vietnamese lichen flora. These collections included several species of Coenogonium [C. dilucidum (Kremp.) Kalb & Lücking, C. minimum (Müll. Arg.) Lücking and C. subluteum (Rehm) Kalb & Lücking], of which the most common are C. dilucidum and C. minimum. Most interesting was the discovery of an isidiate species, Coenogonium disciforme Papong, Boonpragob & Lücking, both with and without fruiting bodies. The sterile specimens of this taxon were reported from all the localities, while fertile specimens are known only from Chu Yang Sin National Park (100484). Previously the species has been reported from Thailand and Australia (Queensland) and until now no account of fertile C. disciforme was available. The fertile specimens cited here represent the first confirmed presence of fruiting bodies in this taxon. The taxon was found growing on the leaves of understorey shrubs and trees and is described here in detail.
Coenogonium disciforme Papong, Boonpragob & Lücking
Lichenologist 39: 47 (2007).
(Fig. 1)
Fig. 1. Coenogonium disciforme. A, distribution in Vietnam; B & C, a fertile specimen (T. T. Nguyen 100484); D, vertical longitudinal section through apothecium; E, mature spores. Scales: B = 0·5 mm; C = 0·1 mm; D = 20 µm; E = 5 µm.
Thallus epiphyllous, crustose, smooth, laciniate, greyish green, 17–19 µm thick. Isidia disc shaped, plane to ±convex, few to numerous, shortly stalked, 0·1–0·2 mm diam., leaving regular rounded holes in the thallus after their detachment. Photobiont Trentepohlia, cells angular, arranged in irregular plates.
Apothecia few, epiphyllous, sessile, scattered, rounded, biatorine, 0·1–0·13 mm diam. and 100–110 µm high; disc slightly concave to plane, pale yellow to yellow. Margin thin, distinct, smooth, ±raised above the level of disc, concolorous or paler than disc. Excipulum well-developed, paraplectenchymatous, 15–30 µm broad, colourless, I−. Hypothecium 12–15 µm high, colourless, I−, KI−. Hymenium 25–30 µm high, colourless, I−, KI−. Paraphyses unbranched, 1–1·4 µm thick, with thickened apices (2·5 µm). Asci cylindrical, 22–27 × 3–4 µm, thin walled, without tholus. Ascospores 8 per ascus, irregulary biseriate, narrowly ellipsoid, 1-septate, 7–8 × 2–2·5 µm, 3–4 times as long as broad.
Pycnidia not observed.
Ecology and distribution. Eastern Palaeotropics (Rivas Plata et al. Reference Rivas Plata, Lücking, Aptroot, Sipman, Chaves, Umaña and Lizano2006; Papong et al. Reference Papong, Boonpragob and Lücking2007). It is new to the Vietnam lichen flora and is found growing on the leaves of understorey trees in montane forests at elevations of 132–685 m along with Asterothyrium rotuliforme (Müll. Arg.) Sérus., Echinoplaca sp., Porina sp. and Tricharia sp.
Remarks. The species is closely related to Coenogonium isidiiferum (Lücking) Lücking, which differs in having irregular isidia that do not leave rounded holes on the thallus surface after their detachment. In contrast, isidia in Coenogonium disciforme are regular and leave rounded holes on the thallus surface. In addition, C. isidiiferum is a neotropical species while C. disciforme is strictly a palaeotropical species.
Isidiate species of Chroodiscus mirificus (Kremp.) R. Sant., Porina alba (R. Sant.) Lücking, P. fusca Lücking and P. pseudoapplanata Lücking & Cáceres should not be confused with this taxon. Chroodiscus mirificus differs in having K+ yellow thallus and bigger (0·2–0·4 mm) squamiform isidia, while all the Porina species mentioned above have concave to ±plane isidia that are formed by thallus outgrowths and are composed of radiate fungal hyphae associated with short, algal threads. For further description readers are referred to Lücking (Reference Lücking2008) and Santesson (Reference Santesson1952).
Specimens examined. Vietnam: Quang Binh Prov.: Phong Nha Ke Bang National Park, N17°28′51·6″, E106°18′39·1″, alt. 136 m, on leaves, 2010, T. T. Nguyen 100007, 100027a (KoLRI); N17°33′04·2″, E106°18′03·6″, alt. 132 m, on leaves, 2010, T. T. Nguyen 100168f (KoLRI). Thua Thien Hue Prov.: Bach Ma National Park, N16°12′55·50″, E107°51′40·20″, alt. 685 m, on leaves of Ochna spp., 2010, T. T. Nguyen 100448, 100449 (KoLRI). Daklak Prov.: Chu Yang Sin National Park, N12°27′07·10″, E108°20′20·30″, alt. 430 m, on leaves, 2010, T. T. Nguyen 100483, 100484 (KoLRI).
We are grateful to Drs R. Lücking and L. Lőkös for critically reviewing the manuscript; and to Sunchon National University for providing the laboratory facilities. This work was supported by grants from Higher Education Project 2, Vietnam (HEP 2) and the Basic Research Promotion Fund (MOEHRD, KRF-2008-313-C0081) through National Research Foundation of Korea (NRF). The first author also thanks Mr Xin Yu Wang, for his help and kindness.
