Lejeuneaceae (Marchantiophyta) from a species-rich taphocoenosis in Miocene Mexican amber, with a review of liverworts fossilised in amber

We describe a diverse taphocoenosis in a piece of Mexican amber that includes two morphotypes assignable to the leafy liverwort family Lejeuneaceae, an angiosperm seed, a putative bud scale, dematiaceous hyphomycetes as well as dipteran and hymenopteran insects belonging to Phoridae (genera Megaselia, Puliciphora, and Apocephalus), Cecidomyiidae, Psychodidae and Mymaridae (genus Alaptus). Liverworts are known from eight amber deposits but have only rarely been observed in Mexican amber. A perianth-bearing liverwort gametophyte in the piece of amber is classified as Mastigolejeunea extincta sp. nov., and several sterile gametophytes are described as Ceratolejeunea sublaetefusca sp. nov. With these new species, approximately 60 liverworts have been described from amber to date. Remarkable syninclusions include a hyphomycete which is the first darkly-pigmented filamentous microfungus with clear reproductive structures reported from Mexican amber. Fourier Transform Infrared Spectroscopy of a fragment of the investigated amber piece revealed a “Type I” Mexican amber. A whole solubility test suggested a mature resin, although the resin was not much oxidized during the process of amberization. Available evidence suggests that the amber was produced by a Hymenaea tree and that the resin was exposed on its bark, behaving as a sticky trap for insects and vascular plant fragments, and also embedding some epiphytic liverworts and fungi.