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The present investigation examines the oogenesis of the gleichenioid fern, Diplopterygium glaucum (Thunb. ex Houtt.) Nakai using transmission electron microscopy. The results demonstrate that the oogenesis of D. glaucum is similar to the core leptosporangiate ferns. The egg cell of D. glaucum was progressively isolated from the adjacent cells by forming a separation cavity and an egg envelope during maturation. However, during this process, a pore region consistently connected the egg and the ventral canal cell. Ultimately, a fertilization pore formed at the pore region when the egg matured. The nucleus produced conspicuous evaginations during later stages of egg development. The cytological features during oogenesis in D. glaucum more closely resembled the core leptosporangiate ferns rather than the basal leptosporangiate ferns (Lygodium and Osmunda), which possess no egg envelope or fertilization pore. The results provide new characteristics for interpreting the evolutionary history of the gleichenioid ferns.
Alpine vegetation is one of the most restricted ecosystems in Mexico. Its greatest extent occurs on the high peaks of the Trans-Mexican Volcanic Belt (TMVB). In this study we document fern diversity of the alpine vegetation of central Mexico, generate a floristic list, provide a key for determination, and report the elevational limits of the species present. The latter information will serve as a baseline for future comparisons to determine potential upward migration of fern species, as is predicted with global warming. In comparison to the páramo vegetation of Central and South America, fern diversity in the alpine vegetation of central Mexico is surprisingly low, and only five families, 11 genera, and 12 species are documented. This represents 1.5% of the ferns species known from the country. Polypodiaceae is the most diverse family, with four genera and four species, followed by Pteridaceae (three genera and three species) and Dryopteridaceae (two genera and two species). Aspleniaceae and Woodsiaceae each have a single genus, the former with two species and the latter with one species. All of the alpine ferns growing in the TMVB are leptosporangiate, and there are no arborescent, epiphytic, aquatic, or heliophilous ferns. Asplenium castaneum, Cystopteris fragilis, and Polystichum speciosissimum are widespread in the alpine vegetation, whereas the remaining species are restricted to one or few sites. With regard to upper elevational limit, the highest occurring species were Asplenium castaneum (4,569 m), Polystichum speciosissimum (4,490 m), and Cystopteris fragilis (4,377 m).
The present study describes the anatomy of Anemia villosa, Anemia organensis, and a hybrid of the two species (Anemia villosa x Anemia organensis). The aim of the present study was to answer the following question: can the Anemia villosa x Anemia organensis hybrid be distinguished from the parent plants based on its anatomical traits? The results showed that the two species and hybrid can be easily differentiated by their anatomical characteristics and that the hybrid anatomy shares features with both parents. In addition, the hybrid differed from the parents in two variables: leaf thickness and number of trichome cells.
The American tree fern Dicksonia sellowiana reaches its northern distribution limit in Mexico. This species grows only in the highly fragmented remnants of the montane cloud forest (MCF). Given the lack of data on ecological aspects of this endangered tree fern species, considered under special protection by Mexican legislation, the objectives of the present research were to investigate the structure of D. sellowiana populations and to characterize its habitats. The study was carried out in seven populations located at different elevations and latitudes in the MCF of the Sierra Madre Oriental in Mexico. In each locality, three sampling plots were established to characterize the habitat and to record density, height, stem diameter, number of leaves, and individual fertility. The resulting values were analyzed with univariate and multivariate statistics. In four of the D. sellowiana populations, individuals of low height predominated; these were classified as dynamic populations. However, the density of individuals by unit area was low compared with some South American populations, probably because of the high degree of fragmentation of the MCF. The variation in population density was mainly explained by the vegetation cover. Environmental factors such as elevation and slope orientation, however, explained better the variation of the basal area of tree fern populations. These results constitute the first reference on the current state of Mexican D. sellowiana populations, which is important for the management and conservation of this endangered species, and for monitoring changes in the environmental conditions of its natural habitat, the MCF of Mexico.