The response to the canopy openness of species in tropical forests is a source of niche differentiation. The tree ferns Alsophila firma, Cyathea divergens and Lophosoria quadripinnata coexist in a cloud forest in Mexico; the first is abundant in creeks, the second occupies slightly open places, and the third prefers more open sites. We hypothesized that the distribution of these species would be correlated with their germination patterns. To test the hypothesis we evaluated the effect of light, water potential and canopy openness on spore germination. Spores were incubated under different light filters modifying red∶far-red ratio or light intensity, water potential was modified with polyethylene glycol solutions and distinct canopy openness were selected in the field. No germination occurred in darkness, and it was low under red light and far-red light; however, all species germinated at a very low photon flux density (PFD, 0.04 µmol m⁻² s⁻¹). The decrease of water potential from 0 MPa to −0.7 MPa reduced germination in all species, from 98.6% to 72.2% in L. quadripinnata, 66.4% to 18.9% in A. firma and 74.2% to 4.1% in C. divergens. The increase of the canopy openness reduced the germination capacity of the three species, but L. quadripinnata was the least affected. The germination requirements of the three tree fern species were partially related to the distribution of the sporophytes in the cloud forest.

The patterns of geographic differentiation in fern species have been linked to climatic differences across regions and the distribution of available habitat. In this paper, the association between some climatic features and patterns of geographic differentiation in American tree ferns was evaluated. For this, the occurrence ranges of 190 species were plotted and then analysed using track analysis. Here we identify six generalised tracks that span the main highland regions of tropical America: the Andes, the Guyana Highlands, the Brazilian Atlantic coast, lower Central America, the Greater Antilles, and upper Central America-Mexico. We did not find an association between cloud forest habitat and the differentiation pattern revealed by generalised tracks in Central America. Instead, these patterns are congruent with well-documented geological boundaries in the region. Climatic variables associated with cloud forest habitat were extracted from each generalised track and subjected to ANOVA, showing that most tracks have equivalent climates. The Andean track showed significant climatic differences with the Brazilian and Guyanan tracks, which were associated with main habitat discontinuities. From these results, we propose that historical isolation has been important in promoting geographical differentiation in tree ferns and that differentiation by dispersal cannot fully explain the large-scale geographical patterns observed in tree ferns.

An illustrated key based on morphological, ecological and geographical characteristics is presented for the Isoëtes taxa of the Coastal Plain, Piedmont and the eastern side of the Appalachian Mountains of Alabama, District of Columbia, Delaware, southern Maryland, North Carolina, South Carolina, Florida, Georgia, Mississippi, eastern Louisiana, southeastern Tennessee and eastern Virginia. The key includes 22 species, three additional subspecies/ varieties and nine sterile hybrids. It is primarily intended to serve as an investigative tool to assist field botanists engaged in conservation, floristic and ecological studies in the Southeast.

Two species of Isoëtes (Isoëtaceae) occur in the Kamchatka Peninsula, northern Russian Far East — I. asiatica (Makino) Makino and I. maritima Underw. The distribution and ecology of these species are discussed. A hybrid of these species was found alongside its parental species in south Kamchatka in the shallows of a lake impacted by humans, and it is formally described here as I.×paratunica D. F. Brunton, Mochalova & A. A. Bobrov. It is the first Isoёtes hybrid discovered in Russia.