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Diverse temperate forest types and a high atmospheric humidity have recently been suggested for the Eocene source area of Baltic amber. However, ferns are astonishingly rare as inclusions in this amber, which is in contrast to other seed‐free land plants, fungi, and lichens. Moreover, the identities of some of the few described putative fern taxa are dubious, and some fossils were even assigned to the Paleozoic seed fern genera Alethopteris, Pecopteris and to the form genus Sphenopteris containing Paleozoic and Mesozoic fern‐like leaf fossils. Here, we review previously described fern inclusions from Baltic amber and identify further fern‐like leaf inclusions as belonging to the extant angiosperm genus Comptonia (sweet ferns, Myricaceae). We conclude that only one taxon, Matonia striata (Matoniaceae), can with confidence be identified as a Polypodiopsida representative. Although “Pecopteris” humboldtiana is so far only known as sterile foliage, its leaf morphology strongly suggests that also this taxon belongs to the Polypodiopsida rather than to any other tracheophyte lineage. We propose accommodating “Pecopteris” humboldtiana in the new genus Berendtiopteris. “Alethopteris” serrata and “Sphenopteris” phyllocladoides are not to be regarded as evidence of ferns from Baltic amber. Reinvestigation of the holotypes of these two taxa did not reveal to which tracheophyte lineages these fossils belong. We suggest that the scarcity of fern remains from Baltic amber may reflect both a relatively low fern diversity in the source area of the fossil resin, and an absence or rarity of epiphytic and climbing ferns as observed in modern temperate forest ecosystems.

Divergence time estimates suggest that most clades constituting the fern family Pteridaceae (Polypodiales) were in existence by the Early Cretaceous. However, fossil evidence to corroborate this remains exceedingly rare. Burmese amber is an important source of new information on the radiation of derived fern lineages during the Cretaceous Terrestrial Revolution. This study describes Heinrichsia cheilanthoides gen. et sp. nov., a fern with suggested affinities to Pteridaceae, based on fertile foliage portions preserved in Early Cretaceous (~100 Ma) amber from Myanmar. Heinrichsia cheilanthoides is characterized by a pinnate‐pinnatifid frond that bears apical, marginal sori protected by a pseudoindusium. Sporangia are of the polypod type and contain tetrahedral‐globose, trilete spores with a striate perine. This discovery provides a new calibration point to test and refine molecular clock‐based concepts of the evolutionary history of the Pteridaceae. Heinrichsia cheilanthoides further substantiates the suggestion that the Cretaceous forests of Myanmar were home to a rich fern flora.

Aim: The processes that shaped the West Indian fern flora remain poorly understood. We attempt to investigate earlier biogeographical patterns described for the region using the genus Adiantum as model. These patterns propose that the West Indian fern flora has (1) an essentially continental rather than insular character, having a rich representation of species occurring in tropical America;(2) the Greater Antilles have a higher fern diversity and higher endemism than the Lesser Antilles, and (3) adaptive speciation has been an important process in shaping the fern diversity of the Greater Antilles. Location: West Indies. Methods: Adiantum is a subcosmopolitan genus that comprises 200-225 species of which 33 occur in the West Indies. We compiled the most comprehensive molecular dataset of Adiantum available to date, including the chloroplast markers rbcL, atpA, atpB and trnL-F of 407 accessions belonging to 101 species, 24 of which occur in the West Indies. Maximum likelihood and Bayesian inference approaches were applied to generate phylogenetic hypotheses. Divergence times were estimated using published substitution rates. Ancestral areas were estimated using BioGeoBEARS. Results: The extant West Indian Adiantum species originate from at least 17 predominantly Miocene immigration events, 11 from South America and six from Central America, in combination with two cladogenetic events. The Cuban endemics Adiantum alomae and A. sericeum, as well as the Greater Antillean A. deltoideum, A. cristatum and A. pyramidale first appeared during the Pleistocene. The emergence of A. alomae and A. deltoideum coincides with the formation of the karstic relief of the Cuban coasts. Main conclusions: Immigration, rather than cladogenesis, governed the evolution of the West Indian Adiantum species. Our results concur with theoretical models proposed for island communities, suggesting that geologically younger and smaller island assemblages mainly derive from immigration, whereas cladogenesis plays an important role in older and larger islands.

Divergence time estimates based on DNA sequence variation of extant species suggest that eupolypod ferns were diverse already in the Cretaceous; however, fossil evidence to support this assumption remains exceedingly rare. Holttumopteris burmensis gen. et sp. nov., a fertile fern foliage fragment preserved in a piece of Albian–Cenomanian Burmese amber from Myanmar, is characterized by divided fertile leaves with catadromous, free lateral veins. Sporangia possess a vertical annulus interrupted by the sporangium stalk and contain monolete spores with a lophate perine. The sporangia occur clustered in discrete sori overarched by a laterally attached, reniform indusium. Reconstruction of ancestral character states suggests affinities of Holttumopteris to the Thelypteridaceae; however, several taxonomically relevant characters are not preserved. This discovery is nevertheless important because H. burmensis represents the first unequivocal fossil of a representative of the eupolypods from the middle Cretaceous.

Polyploidy is widely considered as a major process in the evolution of plants but the accumulation of polyploid species diversity is still controversial. Some recent studies proposed increased extinction risk in neopolyploids compared with their diploid ancestors. The high proportion of polyploid ferns is expected to be formed mainly by neopolyploids, whereas paleopolyploid species are predicted to be clustered in clades founded by whole genome duplications. Here, we test this prediction by exploring the evolution of polyploidy in the derived fern family Aspleniaceae. The family has a global distribution and shows the highest frequency of polyploid taxa among all ferns. To test the hypothesis, we obtained a comprehensive phylogeny using chloroplast DNA sequences of 883 specimens representing 292 species. All published chromosome counts were mapped onto this phylogenetic framework in order to explore the evolution of polyploids. We recovered evidence for several whole genome duplications in the history of Aspleniaceae. Phylogenetic relationships of polyploids exceeding the tetraploid level suggest that tetraploid Asplenium species may have replaced their diploid ancestors as the main evolutionary players in some clades of this family.

Burmese amber is currently the most important source of Cretaceous amber-preserved plants. Recent findings indicate a rich cryptogamic diversity in the source forests of this amber. Besides of liverworts and mosses, several fossils of polypod ferns have been discovered, so far. Here, we report a new fern inclusion from Burmese amber which represents the first leaf fossil of the polypod family Lindsaeaceae. The fossil shows all characteristics of extant Lindsaeaceae, however, it remains unclear if it belongs to an extant or an extinct genus. Along with the sole other Cretaceous Lindsaeaceae fossil, a root fossil from the Albian of North America, the new fossil indicates a wide distribution of this fern family in the Northern Hemisphere during the late Early Cretaceous.

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The monospecific fern genus Cystodium (Cystodiaceae; Polypodiales) occurs exclusively in the tropical forests of the Malay Archipelago, the Admiralty Islands, the Louisiade Archipelago, and the Solomon Islands. Divergence time estimates suggest that the genus originated in the Mesozoic; however, fossil evidence to validate this suggestion has been lacking. Amber from Myanmar (Burmese amber) is an important source of new information on the diversity of vascular cryptogams in the Cretaceous. This paper describes the fossil taxon Cystodium sorbifolioides nov. sp. based on a fragment of a fertile leaf preserved in Burmese amber that represents the first fossil evidence of the family Cystodiaceae. Cystodium sorbifolioides is used to obtain a minimum age estimate for the Cystodiaceae and the closely related, monogeneric Lonchitidaceae and Lindsaeaceae. The fossil strengthens the hypothesis that the forest ecosystems of Malesia and Melanesia represent refugia for many tropical plant lineages that originated in the Cretaceous.

Although a worldwide phylogeny of the bolbitidoid fern genus Elaphoglossum is now available, little is known about the phylogenetic position of the 34 Cuban species. We performed a phylogenetic analysis of a chloroplast DNA dataset for atps-rbcL (including a fragment of the gene atps), rps4-trnS, and trnL-trnF. The dataset included 79 new sequences of Elaphoglossum (67 from Cuba) and 299 GenBank sequences of Elaphoglossum and its most closely related outgroups, the bolbitidoid genera Arthrobotrya, Bolbitis, Lomagramma, Mickelia, and Teratophyllum. We obtained a well-resolved phylogeny including the seven main lineages recovered in previous phylogenetic studies of Elaphoglossum. The Cuban endemic E. wrightii was found to be an early diverging lineage of Elaphoglossum, not a member of E. sect. Squamipedia where it was previously classified. We propose a new section for this species: E. sect. Wrightiana. The early diverging position of E. wrightii is of particular interest because the species is a root climber (i.e., climbing from the soil on the lower portions of tree trunks and not losing its connection with the soil), a growth habit it shares with its closest bolbitidoid outgroup genera. This suggests that holoepiphytism evolved later in Elaphoglossum, and the primary hemiepiphytism of E. amygdalifolium, which is sister to the rest of the genus, was derived independently from ancestors that were root climbers. Based on our phylogenetic analysis and morphological investigations, the species of Cuban Elaphoglossum were found to occur in E. sects. Elaphoglossum, Lepidoglossa, Polytrichia, Setosa, and Squamipedia.