Pycnidial Structures and Genus Concept in the Thelotremataceae

Abstract

The pycnidial characters in eight species of the Thelotremataceae were studied by light microscopy and scanning electron microscopy in order to develop a better understanding of the genus within the family. Three types of conidia can be recognized in the Thelotremataceae: oblong, fusiform, and bacilliform. The species groups recognizable by conidial characters prove to have appropriate apothecial types, according to the concept of M. E. Hale, Jr. Myriotrema andamanicum is transferred to the genus Ocellularia based on apothecial and pycnidial characters and Myriotrema mastarion is a new synonym of Ocellularia andamanica. The family Thelotremataceae includes crustose lichens occurring mainly on bark of trees, and characterized by crater-like apothecia which are unknown in other lichen families. Since Acharius (1803) first described the genus Thelotrema, more than 500 species of the family have been reported. Several attempts at the recognition of and generic divisions of the Thelotremataceae have been attempted. Muiller Argoviensis (1887) recognized four in the Thelotremataceae on the basis of ascospore color and septation: Ocellularia (with colorless, transversely septate ascospores), Phaeotrema (with brown, transversely septate ascospores), Thelotrema (with colorless, muriform ascospores), and Leptotrema (with brown, muriform ascospores). These called spore genera, have been widely accepted by many lichenologists for about a century. Hale (1980) produced a revision of the family in which he recognized three which were based on apothecial features: Thelotrema (with colorless exciple and periphysoids), Myriotrema (with colorless exciple and without periphysoids), and Ocellularia (with carbonized exciple and without periphysoids). These recognized by the apothecial features, are discordant with the spore genera. Although most lichenologists currently accept Hale's others still use the earlier spore genera proposed by Mtiller and the subdivisional classification of the Thelotremataceae remains confused. Pycnidia, which are developed as globose to flask-shaped conidiomata, are the conidia-bearing structures in lichens. It has been found in the last 15 years that pycnidia merit more critical attention at all taxonomic levels. For the recognition of several pycnidial features can be of high taxonomic importance. For example, the presence of unciform or filiform conidia separate Punctelia from the Parmelia (Krog 1982), and minute ellipsoidal conidia distinguish the genus Phaeophyscia from Physcia and Physconia, both of which have longer, subcylindric conidia (Moberg 1977). In the Thelotremataceae, conidiomata have been reported only from three species. Immersed pycnidia producing oblong conidia were observed in Thelotrema concretum (= Myriotrema concretum) (Nylander 1867). The size of conidia in Thelotrema anamorphoides and T. subcaesium (synonym of Myriotrema clandestinum) was mentioned by Nylander (1869) to have value for species recognition. Redinger (1936) and Hale (1974, 1978, 1981), in their monographic studies, did not paid any special attention to pycnidia and conidia as taxonomic characters. The present investigations attempt to establish a more sound classification of the family by the incorporation of pycnidial structures as new taxonomic characters. MATERIALS AND METHODS About 1,200 specimens were examined for the present study, including specimens borrowed from CBM and TNs. Type specimens were also borrowed from H and us for the taxonomic studies. The specimens collected by T Matsumoto are deposited in the herbarium of Hiroshima University (HIRO). Scientific names of the follow Hale (1980). Air-dried materials were used to observe the general appearance of thalli. Photographs were taken by a Nikon FX-35DX with a Nikon dissecting microscope SMZ-U and a Nikon microscope OPTIPHOT-2. Vertical sections of the pycnidia were made by a razor blade under the dissecting microscope for anatomical studies. The measurements and micrographs were made on preparations mounted in lactophenol cotton-blue (LPCB). Scanning electron microscope (SEM) was employed to study the micromorphological structures. Mucilaginous matrix of the pycnidial cavity was removed by a modified method of Anglesea et al. (1982) and Honegger (1984). Thallus fragments were immersed in a 5% solution of the commercially available washing powder Ariel manufactured by P & G and incubated for 3 hr. at 25?C. Although Honegger (1983) incubated for 15 hr., with this long incubating time for the Thelotremataceae whole pycnidia were detached from the thallus. After this treatment, 0007-2745/99/86-91$0.75/0 This content downloaded from 157.55.39.248 on Thu, 28 Jul 2016 04:13:09 UTC All use subject to http://about.jstor.org/terms 1999] MATSUMOTO & DEGUCHI: THELOTREMATACEAE 87