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Patterns of resource allocation reflect the plastic strategies that result from different selective pressures imposed by the environment. However, biomass allocation can be limited by architectural restrictions that change with the plant size. Our knowledge about sex allocation in heterosporous aquatic ferns remains scarce and studies on the reproductive strategies of these plants may yield valuable information regarding the evolutionary history of heterospory. Here, we investigate resources allocation, both in number and in biomass, to produce megasporangia and microsporangia among three species of Salvinia with different body sizes. Salvinia oblongifolia, S. auriculata and S. minima were collected in temporary ponds on the floodplain of the Pandeiros River in Brazil. We counted megasporangia and microsporangia, and measured their dry mass in each ramet. We also measured the total vegetative biomass and total reproductive biomass of each ramet in each species. Resource allocation to megasporangia production is associated with the specific body size of each species. However, the allocation for microsporangia production was higher in the species with intermediate size, which probably may be related to the drought event. The total reproductive biomass of each species was not dependent on the total vegetative biomass, but despite a similar reproductive effort, species differ on which sex is prioritized in the allocation process. Our results provide the first data about the processes underlying the sex allocation of Salvinia in the floodplains. The production of sori is size dependent in each Salvinia species and is shaped by drought, an intense selective pressure in temporary wet habitats. [ABSTRACT FROM AUTHOR]

Herein, we report new fossil remains with marsileaceous affinity associated with dispersed microspores corresponding to Crybelosporites, different types of massulae of Salvianiaceae ( Paleoazolla patagonica and Azolla circinata), and a single megaspore assigned to the fossil genus Grapnelispora. These fossils were recovered from the Late Cretaceous Loncoche Formation, at the Calmu-Co section, Malargüe Group, Northern Neuquén Basin, Mendoza, Argentina. The macrofossils include scattered leaflets, rhizomes, roots, and a sporocarp-like structure. They share characters with members of the aquatic fern family Marsileaceae; however, based on the characters preserved, they could not be placed within any extant or fossil species; therefore, the fossils are better included within a new fossil-taxon, Mendozaphyllum loncochense. Dispersed spores of Crybelosporites pannuceus, also belonging to Marsileaceae, were recovered from the entire section. Additionally, abundant isolated massulae with affinity to the aquatic fern family Salviniaceae, and a single megaspore assigned to Grapnelispora loncochensis, were identified from the plant bearing layer. The presence of Marsileaceae fossils in the Campanian-Maastrichtian Loncoche Formation, Mendoza, extends towards the north the paleogeographical distribution of the family Marsileaceae in Argentina, since previous records are from Patagonia. A fluvial to deltaic environment with lacustrine episodes is suggested by the sedimentology of the lower and middle parts of the Calmu-Co section and supported by the abundant fresh water algae recovered from the palynological association. This was probably the optimum habitat for the growth of aquatic ferns related to Marsileaceae and Salviniaceae and explains its abundance in the studied sediments. [ABSTRACT FROM AUTHOR]

Previous studies have shown that core leptosporangiates, the most species-rich group of extant ferns (monilophytes), have a distinct plastid genome (plastome) organization pattern from basal fern lineages. However, the details of genome structure transformation from ancestral ferns to core leptosporangiates remain unclear because of limited plastome data available. Here, we have determined the complete chloroplast genome sequences of Lygodium japonicum (Lygodiaceae), a member of schizaeoid ferns (Schizaeales), and Marsilea crenata (Marsileaceae), a representative of heterosporous ferns (Salviniales). The two species represent the sister and the basal lineages of core leptosporangiates, respectively, for which the plastome sequences are currently unavailable. Comparative genomic analysis of all sequenced fern plastomes reveals that the gene order of L. japonicum plastome occupies an intermediate position between that of basal ferns and core leptosporangiates. The two exons of the fern ndhB gene have a unique pattern of intragenic copy number variances. Specifically, the substitution rate heterogeneity between the two exons is congruent with their copy number changes, confirming the constraint role that inverted repeats may play on the substitution rate of chloroplast gene sequences. [ABSTRACT FROM PUBLISHER]

Three new taxa from Albian, Early Cretaceous assemblages in Gondwana (Australia and Antarctica) and two previously described fossils from the Late Cretaceous and Eocene of North America are attributable to the heterosporous semi-aquatic fern family Marsileaceae. They are assigned to Marsileaceaephyllum, a morphotaxon erected here for sterile remains (whole plants, and isolated leaves and leaflets) of Marsileaceae. The Gondwanan taxa, Marsileaceaephyllum lobatum and Marsileaceaephyllum spp. B-C, have either a cruciform leaflet arrangement or dichotomous and anastomosing venation characteristic of modern Marsileaceae. Two previously established taxa, Marsilea johnhallii and Marsilea sp., which represent sterile Marsileaceae, are also transferred to the new genus (now Marsileaceaephyllum johnhallii and Marsileaceaephyllum sp. A, respectively). Examination of all fossil venation patterns reveals four new venation types not present in extant taxa, suggesting that most fossil Marsileaceae (leaves) are distinct from extant genera, and are likely members of extinct lineages. This is further supported by the absence of modern megaspore types in the Early Cretaceous. [ABSTRACT FROM AUTHOR]

The taxonomic history of Azolla (Azollaceae) is long and complex. Previous studies have employed morphological, cytological, and molecular data in an attempt to circumscribe the seven extant species, but none has been completely successful. In this study, we employ DNA sequence data from three noncoding regions, two derived from the plastid genome (the atpB-rbcL and trnL-trnF regions) and a third from the internal transcribed spacers of the nuclear rRNA genes. Cladistic analyses of these data confirm the division of Azolla into two major clades, corresponding to the traditional classification of the genus into sections Azolla and Rhizosperma. Moreover, the monophyly of A. pinnata plus A. nilotica (sect. Rhizosperma) contradicts newer classifications of the family, in which these species were placed in different subgenera. In section Azolla, DNA sequence data support several past reports in suggesting that A. rubra and A. filiculoides are distinct species and that A. caroliniana is distinct from both A. microphylla and A. mexicana. However, distinct lineages representing A. microphylla and A. mexicana were not found, and these plants appear to represent a single evolutionary lineage. [ABSTRACT FROM AUTHOR]