Selaginella in Cretaceous amber from Myanmar

Abstract

Selaginella (Selaginellales, Selaginellaceae) is the most speciose genus of lycophytes and, with approximately 750 recognized present-day species, also one of the largest genera of vascular plants. However, the evolutionary history of this species richness remains largely unresolved. Recent research suggests that Selaginella was diverse already in the mid-Cretaceous and shows that S. subg. Stachygynandrum dates back at least to the incipient Angiosperm Terrestrial Revolution some 100 million years ago. Here, we describe 20 new fossil-species of Selaginella based on fertile shoots and spores preserved in mid-Cretaceous Kachin amber from Myanmar and emend the previously described S. cretacea. Ten of the species (S.

Filmy Ferns (Hymenophyllaceae) and Associated Spike-Mosses (Selaginellaceae) from the Mid-Cretaceous Kachin Amber, Myanmar

“…Selaginella is an ancient lineage with fossils dating back to the Carboniferous or even Devonian [ 53 , 85 ]. Schmidt et al [ 23 , 25 ] discovered the presence of hyperdiverse Selaginella in the mid-Cretaceous Kachin amber, Myanmar, including ten species of Selaginella subgenus Stachygynandrum with anisophyllous (bilateral) strobili and eleven species with isophyllous strobili. All these fossil species are erected based on the combination of a series of key characters [ 23 , 25 ].…”

“…Schmidt et al [ 23 , 25 ] discovered the presence of hyperdiverse Selaginella in the mid-Cretaceous Kachin amber, Myanmar, including ten species of Selaginella subgenus Stachygynandrum with anisophyllous (bilateral) strobili and eleven species with isophyllous strobili. All these fossil species are erected based on the combination of a series of key characters [ 23 , 25 ]. Furthermore, Li et al [ 24 ] described a new species of Selaginella subgenus Stachygynandrum with anisophyllous strobili from Kachin amber.…”

“…Schmidt et L. Regalado with monomorphic and decussately arranged vegetative leaves in having dimorphic vegetative leaves arranged in four rows [ 25 ]. Our fossils resemble the rest nine species in the aspects of dimorphic vegetative leaves and isophyllous strobili, but none of the nine species has alary keel on the abaxial side of the midrib of sporophyll [ 25 ]. Alary keel is also not documented in the extant species of Selaginella [ 81 , 84 ].…”

“…Due to the thin filmy laminas, the extant Hymenophyllaceae predominantly live in moist mossy forest [ 45 , 90 ], and the evolution of the filmy ferns shows a tendency towards progressive reduction in size, which may be considered as adaptive to the extremely moist mossy zone [ 45 ]. Additionally, the Kachin Selaginella fossils also possess several characters suggestive of humid conditions, such as the relatively thin leaves often with fungal colonization [ 25 ]. Therefore, the discovery of the filmy ferns and associated spike-mosses from Kachin amber provides additional evidence for the presence of a tropical humid forest located close to the seashore [ 70 , 76 , 91 ] and with a diverse fern flora in the mid-Cretaceous of Kachin area.…”

“…Recent palaeobotanical findings indicate that the mid-Cretaceous Kachin amber deposit of Myanmar is an important source of Mesozoic cryptogams and angiosperms [ 5 , 6 , 7 ], which could provide direct evidence for the above hypothesis. Indeed, a large number of cryptogamic plant inclusions has already been described from Kachin amber, including liverworts [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], mosses [ 20 , 21 , 22 ], lycophytes [ 23 , 24 , 25 ] and ferns [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. As far as ferns are concerned, nine genera and ten species have been reported, most of which could be assigned to the extant families, including Cystodiaceae, Pteridaceae, Dennstaedtiaceae, Marsileaceae, Lindsaeaceae and Thyrsopteridaceae.…”