A new foliicolous fossil-species of Asterina Lév. (Asterinaceae; Asterinales) associated with Calophyllum L. from the Siwalik of Eastern Himalaya and its implications

Abstract

The present study reports and describes a new foliicolous fossil-species of Asterina Lév. (Asterinaceae: Asterinales: Dothideomycetes) namely, A. siwalika sp. nov., on a compressed leaf assigned to modern Calophyllum L. (Calophyllaceae) recovered from the Siwalik sediments (early Miocene to Pliocene: Chunabati Formation) of Darjeeling, Eastern Himalaya. This epifoliar Siwalik fungal species is characterized by a dark brown, sub-dense mycelial mat; septate, branched, superficial, oppositely arranged hyphae with one to two-celled, alternate to oppositely arranged appressoria; flattened, circular, non-ostiolate thyriothecia, scutellum with radially arranged isodiametric to cylindrical cells; and bi-celled, one-septate, conglobate to ellipsoidal, striated ascospores. Here, we reconstruct for the first time a possible sexual life cycle of A. siwalika. The in-situ occurrence of Asterina on Calophyllum leaf cuticles suggests a warm and humid tropical climate and a possible host-parasitic relationship that might have existed in the ancient forest of the Darjeeling sub-Himalaya region during the time of deposition. The conclusion is supported by published qualitative and quantitative climatic data using plant megafossils recovered from the same fossil locality.