Selwyn's Ear-leaf Liverwort
Basis for Listing
Frullania selwyniana (Selwyn’s ear-leaf liverwort) is a rare endemic of eastern North America, within the boreal bioclimatic zone. It has been recorded regionally from Ontario, Wisconsin, and the Upper Peninsula of Michigan. In Minnesota, the species has been recorded in Cook, Lake, and St. Louis counties (Northern Superior Uplands). Frullania selwyniana is restricted to humid paludified swamps dominated by cedar and occasionally from swamps that have cedar and black ash as co-dominants; however, this species appears to prefer to grow only on the bark of older large-diameter Thuja occidentalis (white cedar). Although a targeted survey of the Superior National Forest in 2008 turned up many new locations, they only occurred within this particular microhabitat. Given the species’ narrow geographic range in the state, its specialized and restrictive habitat requirements, and the limited amount of available habitat, Frulliania selwyniana was designated of special concern in 2013.
Frullania selwyniana is a very small species that grows appressed to its matrix. It has an overall copper-red to reddish-brown color, with irregularly branched stems that are light green, becoming brownish with age. Leaves are bi-lobed, with lobes crowded and overlapping, ovate, with entire margins. These dorsal lobes arch across, though scarcely beyond, the main stem. Lobes are convex, with apices decurved. Smaller lobules (hidden underneath the larger main dorsal lobe) are close to the stem and subparallel with it. These lobules are transformed into a small water sac. The lobules have a distinct segment, or stylus, on their inner edge that is very small. An additional flat under-leaf is smaller still, remote to contiguous, obovate to wedge-shaped, and narrowed toward its base along the stem. Frullania selwyniana may be confused with the more common F. eboracensis; however, the latter species does not have the short row of dark brown cells (ocelli) medially in the proximal part of the dorsal lobe that F. selwyniana exhibits (Janssens 2014).
Frullania selwyniana apparently occurs only on the bark of T. occidentalis in dense cedar swamps, where it may be locally frequent (Schuster 1992). Most of the sites in Minnesota are within highly paludified white cedar swamps (i.e. with significant Sphagnum spp. cover; Janssens and Greenlee 2009) such as northern cedar swamp. However, several records are from cedar trees in ecotones between upland and lowland cedar mesohabitat or in mixed hardwood-conifer or shrub-conifer swamps such as northern wet cedar forest or northern wet ash swamp. It appears that patches of the species tend to be found on the upward-facing bark of leaning trees, usually directed towards a canopy opening.
Biology / Life History
Frullania selwyniana is an autoicous (male and female reproductive organs in separate inflorescences on the same plant) species.
Conservation / Management
Climate change may alter the cedar and black ash swamp habitat in which F. selwyniana is found, such that these areas may experience drought stress, increases in insect or disease diebacks, or increased moisture stress (where sites become too wet). Roads may also have an effect on the hydrology of these swamps, impacting the sites in similar ways (i.e., through drought stress or flooding). Additionally, the Emerald Ash Borer (Agrilus planipennis) is a very destructive insect pest of ash trees (Fraxinus spp.), which are the only known host of this borer in North America, and has already killed tens of millions of trees. As such, this destructive beetle could have significant impacts on swamps where black ash is present and thus on F. selwyniana. Furthermore, because many of the old-growth cedar forests in Minnesota are senescing (deteriorating with age), and cedar swamps in general are threatened by poor regeneration, habitat availability will likely be a limiting factor for this species (Janssens 2005).
Best Time to Search
The best time to search for Frullania selwyniana is from May through September or essentially anytime the ground is not covered by snow.
Erika R. Rowe (MNDNR), 2018
(Note: all content ©MNDNR)