Conservation of rare ferns requires identification and management of drivers of species declines. Here we focus on potential threats of invasive earthworms introduced from Europe and Asia on the threatened American hart's-tongue fern (Asplenium scolopendrium var. americanum). Earthworms are ecosystem engineers that alter physical and chemical soil properties and can trigger cascading effects on plant and soil communities. Using a paired field sampling and mesocosm study approach, we sought to assess the potential impact of earthworms to A. scolopendrium. We sampled earthworms at eight A. scolopendrium populations in New York State and documented widespread occurrence of a diversity of invasive earthworms in seven fern populations. Fern populations exist mid-slope and earthworm biomass was higher upslope than within or downslope of fern populations. In a two-year mesocosm experiment we evaluated impacts of two epi-endogeic earthworms (Lumbricus rubellus and Metaphire hilgendorfi) on A. scolopendrium gametophytes and young sporophytes by adding earthworm treatments to potted plants and following growth and survival of fern transplants. While L. rubellus reduced gametophyte survival and number of leaves produced by transplanted ferns, we found no effect of M. hilgendorfi on survival, number of leaves or leaf size. Our findings indicate negative, but limited, impacts of one invasive earthworm species on fern early life stages. Our results suggest that impacts on existing fern populations could be low, as few earthworms were detected within fern populations. Continued assessment of earthworm invasions and other associated stressors is necessary to inform future management and conservation efforts to facilitate A. scolopendrium recovery.

Two closely related bracken (Pteridium) species, P. caudatum and P. aquilinum ssp. pseudocaudatum, have mostly separate ranges that overlap in Peninsular Florida. Congeneric species that occupy similar niches in distinct geographic ranges but whose native ranges narrowly overlap present an eco-evolutionary conundrum: How can species evolved to occupy similar niches in distinct ranges coexist? Research suggests that for a stable coexistence the species should differ at least subtly in their ecological niches, otherwise their coexistence would be unstable. We investigated whether these bracken species share a habitat and co-occur locally, and whether their coexistence is predicted to be stable. We surveyed bracken populations from seven sites at Archbold Biological Station (Venus, Florida, USA) and characterized their biotic and abiotic microhabitat. Both bracken species co-occur at three sites. The two species showed significantly different trends in canopy cover and in response to fire frequency, and they grew at different densities and biomass. These results suggest these two bracken species coexist stably by occupying distinct ecological niches.

This paper resurrects Adiantum weatherbyanum, an overlooked species that occurs in northern Chile, and describes and illustrates a new species, A. rodriguezii, from central Chile. Both taxa belong to the Adiantum poiretii group and were overlooked by the previous authors who worked on the Flora of Chile. Adiantum weatherbyanum is easily recognized by the combination of having of simple and branched, whitish, eglandular hairs on the laminar tissue and veins of the pinnules abaxially, and short ciliate rhizome scales. Adiantum rodriguezii is distinct by its pubescent pinnules on both surfaces; the hairs are simple, articulate, 0.5–1.2 mm long, light brown, with eglandular apices, and restricted to the pinnule veins. Relevant taxa are provided with descriptions, comments, and illustrations of the diagnostic characters.