Trichocolea tomentella (Ehrhart) Dumortier
A Species of Liverwort
Basis for Listing
Trichocolea tomentella (down liverwort) was first recorded for the state in 1875 by I.A. Lapham but without an exact location (Schuster 1953). The species is disjunct to oceanic and suboceanic regions in the northern hemisphere, within the temperate bioclimatic zone (Schuster 1966). Regionally, it has been recorded from Ontario, Wisconsin (Schuster 1953), and the Upper Peninsula of Michigan (Janssens 2010). In Minnesota, about a dozen populations of T. tomentella have been documented in Cass, Itasca, St. Louis, Lake, Carlton, and Pine counties (Laurentian Mixed Forest Province) between 1992 and 2013. The general senescence of old-growth cedar forests in Minnesota and their poor regeneration as a result of deer browsing are serious concerns that threaten the long-term viability of the species’ customary mesohabitat (Janssens and Greenlee 2009). A dedicated search of potential habitats across all districts of the Superior National Forest was conducted in 2008, but no new T. tomentella populations were discovered (Janssens 2008). On the basis of extreme rarity, documented habitat loss, and perceived threats, Trichocolea tomentella was listed as a threatened species in 2013.
At first glance, T. tomentella could be mistaken for a robust weft-forming moss. However, the species is a large (10-15 cm [4-6 in.] long individual plants) distinctive, leafy liverwort, with 2-3-pinnate branching, forming expansive wefts. Belonging to the Ptilidiinae, T. tomentella share with other suborder members the highly ciliate aspect of its leaves (Schuster 1969), which lend the plant a fuzzy macroscopic appearance. It has a very characteristic light- or whitish- to yellowish-green color, contrasting distinctly with the much darker weft-forming mosses among which it grows. Its leaves are highly lobed, the narrow lobes fringed by frequently branched cilia. The large underleaves are nearly completely reduced to cilia. It is differentiated from the other leafy ciliate liverworts in Minnesota (Ptilidium pulcherrimum and P. ciliare; Schuster 1953; and Blepharostoma trichophyllum; Janssens 2010) by its large size and pinnate branching. The leaf lobes in the Ptilidium species are less reduced and more obvious when viewed with a hand lens; those of the very tiny B. trichophyllum (5-10 mm [0.2-0.4 in.] long) are completely resolved as uniseriate cilia.
Trichocolea tomentella is found in highly minerotrophic (high pH) black ash/conifer and cedar swamps and also along the banks of mountain streams and seepage over wet rocks (Schuster 1969). It is absent from acid peatland sites. In swamps, it grows as large wefts on the moist, forest floor and in the large depressions among the trees. Small patches and scattered plants are also found mixed within the wefts of feather mosses. In Minnesota, it occurs in Northern Wet Ash Swamp, Northern Cedar Swamp, Northern Rich Tamarack Swamp, and Northern Wet Cedar Forest. Common associated bryophytes within the Minnesota mesohabitat are the Thuidium species T. delicatulum and T. recognitum, Callicladium haldanianum, Sphagnum warnstorfii, Marchantia polymorpha/aquatica, Plagiomnium ellipticum, Rhizomnium magnifolium, and Rhytidiadelphus triquetrus (Janssens 2010).
Biology / Life History
As a perennial stayer, dweller type (During 1979; 1992), we can assume the species has the potential to form long-lived populations. However, it appears to be quite unable to cope with inundation and tolerates only limited amounts of sediment accumulation (Schuster 1969).
Conservation / Management
Minnesota’s climate may transition to one that is too continental (hot and dry summers during drought periods) for the species to persevere here, as it occurs at the western periphery of its present range. The Cass County Chippewa National Forest specimen is the farthest westward record of the species on the continent (Schuster 1969; Janssens 2010). Climate change might eliminate any remaining populations. Additionally, populations recorded in Minnesota are all associated with wetlands or groundwater seepage areas, which may also be severely impacted by climate change.
Best Time to Search
The best time to search for T. tomentella is from May through September or essentially anytime the ground is not covered by snow.