New Coenogonium species (Ostropales: Coenogoniaceae) from Thailand, new reports and a revised key to the species occurring in the country

A revision of 159 Coenogonium collections from Thailand preserved in RAMK, herb. K. Kalb and herb. K. & J. Kalb is presented. 18 species (including 1 doubtful) could be delimited, three of which are described as new to science, namely C. convexum which differs from the similar C. nepalense by smaller and convex apothecia already at a very early stage of development, C. subborinquense which has larger apothecia (almost double the size) than the similar C. borinquense and C. verrucimarginatum which differs from C. coronatum by having denticulate-verrucose margins of the apothecia. Coenogonium barbatum, C. epiphyllum, C. frederici, C. leprieurii and C. queenslandicum are new additions to the Thai lichen biota. C. disciforme is synonymized with C. isidiiferum. The peculiar vegetative propagules in this species, hitherto named isidia, are described as thallodiscs. Photographs showing the habitus of the species as well as characteristic structures are given and a dichotomous key for the identification of all species is provided.