Ferns and lycophytes are unique among land plants in having two independent life stages, the haploid gametophyte generation and the diploid sporophyte generation. While in most species the sporophyte is the dominant, long-lived portion of the life cycle, in some ferns the gametophyte is capable of sustained vegetative growth, and a number of species produce sporophytes only in parts of their geographic range (a pattern known as the separation of generations). One such species is the Hawaiian filmy fern Callistopteris baldwinii, whose growth form varies across elevational gradients. This species occurs as independent gametophytes near sea level, produces dwarfed sporophytes at mid elevations, and at the highest elevations—where precipitation is greatest due to the orographic uplift of trade winds—it grows as large, mature sporophytes. We measured temperature, relative humidity, and precipitation for several populations of this fern on the island of O‘ahu in Hawai‘i to determine whether these environmental factors may influence the spatial separation of generations exhibited by C. baldwinii on the island. Our results indicate that temperature and precipitation vary across life stages of C. baldwinii, underscoring the key role environmental conditions play in the completion of the fern life cycle.

Increased nutrient supply can have drastic effects on natural ecosystems, especially in naturally nutrient-poor ones such as most tropical rainforests. Many studies have focused on the reaction of trees to fertilization, but little is known about herbaceous plants. Ferns are a particularly common group in tropical forests, spanning all vegetation types and zones. Here, we assess how seven years of moderate addition of nitrogen (N), phosphorus (P), and N+P along an elevational gradient (1000–3000 m) have impacted richness and composition of fern and lycophyte assemblages in tropical montane rain forests growing on naturally nutrient deficient soils in the Ecuadorian Andes. We found that fertilization does not affect overall species richness, but that there were strong differences in species abundances (∼60% of species), both negative and positive, that were apparently related to the systematic affiliations and ecological properties of the affected species. These diverse responses of ferns to fertilization provide insight into the sensitivity and complexity of the relationships of nutrient availability and community composition in tropical forests.

Relative to other vascular plants, ferns have been overlooked with respect to the potential for nonnatives to spread into natural areas and potentially displace native species. An unusual site in the Piedmont of northeast Georgia was found to harbor two species of nonnative ferns that have clearly become naturalized. A third species at the site represents the appearance in a natural setting of another nonnative fern species whose cultivars and hybrids are being more widely planted as ornamentals. Examination of herbarium specimens from Georgia and the Southeastern United States clarified the status of some earlier records and some overlooked records, based on misidentifications or questionable status as naturalized. The species involved (Arachniodes simplicior, Polystichum polyblepharum, and Anisocampium niponicum (=Athyrium niponicum)) are all introductions from temperate regions in East Asia and probably represent escapes from cultivation via spores. The appearance of these species in natural communities raises questions about their potential to spread farther and to become pests by crowding out native flora. The invasive potential of these three species and five other species discussed in a previous paper is evaluated based on field observations as well as information about their status as an epiphyte or ground dweller, reproductive plasticity, ecological requirements, and popularity as horticultural ornamentals.

Most species in the genus Selaginella (Selaginellaceae) are susceptible to desiccation, while a few species are able to withstand the extreme desiccation, recover metabolic functioning, and grow rapidly after rehydration. However, there is limited information about the anatomical features of the resurrection species in Selaginella. In the present study, we compared the microphyll micromorphology and ultrastructure of two resurrection species (S. pulvinata and S. sanguinolenta), and two non-resurrection species (S. kraussiana and S. chrysocaulos). Compared with the two non-resurrection species, the two resurrection species had most of their stomata distributed on the adaxial surface of microphylls that were tightly attached to stems, and possessed smaller and thicker microphylls, smaller stomatal size, higher stomatal density, thicker epidermal cell walls, more chloroplasts, and denser cytoplasm. These micromorphological and ultrastructural features of the two resurrection species were beneficial in reducing the transpiration and dehydration damage and could be considered as ecological adaptations to xeric environments.