This study used existing databases to test the hypothesis that fern species harbor fewer pathogen species than angiosperm species. Analysis was limited to fungal pathogens because of their visibility and to herbaceous perennial dicots (forbs) because they have a similar growth form to ferns. From complete listings in the United States Department of Agriculture plant-fungal database, the number of pathogen species recorded on 200 randomly chosen ferns and herbaceous perennial dicot species were assessed. To control for differences in study effort, the number of citations to these species in the Web of Science was determined. The results showed that the major predictor of the number of fungal pathogen species known to occur on a plant species was study effort, but after controlling for this, the likelihood of a fern species being recorded as having a fungal pathogen species was much less than that for a forb. When pathogens were present, there were approximately 50% fewer pathogen species recorded on fern species than on forb species. This pattern is present even though fern species were cited on average more often than forb species, and it is consistent with impressions in the literature from studies in other parts of the world. Testable hypotheses to explain this difference are evaluated in the context of evolutionary processes leading to variation for pathogen incidence in different phylogenetic lineages, but the physiological or molecular processes that determine the higher resistance of ferns to fungal pathogens remain unknown.

Compared to most other groups of vascular plants, ferns have been neglected with respect to the potential for nonnative species to invade native plant communities and displace native species. Targeted collecting in the Piedmont of northeast Georgia uncovered five nonnative ferns that represent range extensions or provide clear confirmation of naturalization. Examination of herbarium specimens from Georgia revealed that some earlier records, as well as some overlooked records, were based on misidentifications. The species involved (Cyrtomium fortunei, Deparia petersenii, Dryopteris erythrosora, Macrothelypteris torresiana, and Pteris multifida) are all introductions from temperate regions in East Asia and represent escapes from cultivation. Study of Georgia collections held in herbaria from throughout the Southeast allowed determination of the first appearance and subsequent range expansion of the five species over time. These data and information about mating systems, ploidy level, and ecological requirements of each species allowed inferences to be made about their probable spread in the future, including effects of climate change.

Hawaii is home to four species in the fern genus Diplazium: Diplazium arnottii, D. esculentum, D. molokaiense, and D. sandwichianum. Three are endemic to the Hawaiian Islands, and one is introduced and naturalized (D. esculentum). They vary in frequency, from very abundant (D. sandwichianum) to rare and critically endangered (D. molokaiense). Prior to this work, the phylogenetic relationships of only D. esculentum had been estimated due to lack of information available about these species. In this study, we inferred phylogenetic relationships of the Hawaiian Diplazium based on six chloroplast regions – atpA, atpB, matK, rbcL, rps4+rps4–trnS IGS, and trnL intron+trnL–trnF IGS. We downloaded these plastid markers from GenBank for an additional 83 Diplazium species and two Athyrium species, and used the latter as outgroups. The resulting phylogeny inferred from combined data indicated that D. arnottii and D. sandwichianum are sister taxa, likely with origins in the Paleotropics. Morphologically, the two species can be distinguished by leaf dissection and lengths of sori. Diplazium molokaiense is sister to the Asian D. heterocarpum (among our sampled taxa). Diplazium molokaiense is distinguished from other species in the clade by its large sori and longer fronds. Our results reveal the phylogenetic placements of three Diplazium species and corroborate the placement of a fourth species.

The vascular architecture of the stem–the stele–is one of the most well studied topics in pteridology, and has fascinated botanists for more than 200 years. Stelar architecture has attracted much attention, in part, due to its diversity in the fern lineage as well as its use as a stable taxonomic character for circumscribing species, genera, families, or larger informal clades. One aspect of stelar morphology that has garnered specific attention is polystely: the development of multiple concentric cylinders of vasculature. This feature has evolved in lineages throughout the fern phylogeny, including in the genus Pteris L. (Pteridaceae). Here, I describe a polycyclic solenostele as a new synapomorphy for Pteris sect. Litobrochia. The identification of this character as a synapomorphy furthers our understanding of the morphological evolution and circumscription of Pteris as well as aides in species identification within this speciose genus.