Ceratopteris chunii and Ceratopteris chingii (Pteridaceae), two new diploid species from China, based on morphological, cytological, and molecular data.

Understanding how natural hybridization and polyploidizations originate in plants requires identifying potential diploid ancestors. However, cryptic plant species are widespread, particularly in Ceratopteris (Pteridaceae). Identifying Ceratopteris cryptic species with different polyploidy levels is a challenge because Ceratopteris spp. exhibit high degrees of phenotypic plasticity. Here, two new cryptic species of Ceratopteris, Ceratopteris chunii and Ceratopteris chingii, are described and illustrated. Phylogenetic analyses reveal that each of the new species form a well-supported clade. C. chunii and C. chingii are similar to Ceratopteris gaudichaudii var. vulgaris and C. pteridoides, respectively, but distinct from their relatives in the stipe, basal pinna of the sterile leaf or subelliptic shape of the fertile leaf, as well as the spore surface. In addition, chromosome studies indicate that C. chunii and C. chingii are both diploid. These findings will help us further understand the origin of Ceratopteris polyploids in Asia.

Documenting the Sporangium Development of the Polypodiales Fern Pteris multifida.

Reconstructing the development of sporangia in seed-free vascular plants provides crucial information about key processes enabling the production of spores that are important in the life cycle of these plants. By applying fluorescence imaging in intact tissues using dyes and confocal microscopy, this study aimed to reconstruct the key steps during the development of sporangia. Special emphasis was taken on the cell wall structures of tapetum and spore mother cells that have been challenged by microscopical documentation in the past. After staining the cell wall and cytoplasm using calcofluor white and basic fuchsin, the sporangium development of Pteris multifida was observed using confocal microscopy. The clear cell lineages from the sporangial initial cell to stalk, epidermis, inner tapetum, outer tapetum, and sporogenous cells were revealed by confocal imaging. The sporangium development improved in this work will be useful for a general understanding of fern spore formation.

Ultrastructural and cytochemical studies on oogenesis of the fern Pteridium aquilinum.

Egg development in Pteridium aquilinum var. latiusculum was studied using ultrastructural and cytochemical methods to examine structural features influencing fertilization in leptosporangiate ferns. Ultrastructural observations indicate a separation cavity is first formed above the egg during oogenesis with a pore region persistently connecting the egg and the ventral canal cell. The egg envelope is formed by deposition of amorphous materials in the separation cavity on the outer surface of plasmalemma. The egg envelope was not formed across the pore region; instead, a fertilization pore was formed. During oogenesis, the egg nucleus produced extensive evaginations containing osmiophilic bodies. Cytochemical experiments revealed that the egg envelope displays strong periodic acid-Schiff reaction indicative of polysaccharides, with negligible Sudan black B staining for lipids, suggesting that the egg envelope is composed principally of polysaccharides, and not lipids. The present manuscript provides new insights into egg structure and development of Pteridium, including discovery and characterization of the fertilization pore and observations on the chemical nature of the egg envelope, thus contributing to the understanding of the cytological mechanism of the sexual reproduction of ferns.