Bryoxiphium norvegicum (Brid.) Mitt.
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Basis for Listing
Bryoxiphium norvegicum (sword moss) has a scattered northern hemisphere distribution, without zonal affinity (Pursell 2007). In continental North America it is considered a glacial relict that survived in the Driftless Area (Paleozoic Plateau) during the last glaciation (Steere 1937). It has been recorded regionally from Iowa and Wisconsin, and a single Minnesota population was observed in The Blufflands of Winona County by J. M. Holzinger sometime between the years of 1893-1905. Unfortunately, despite extensive searches, the Minnesota population is believed to have been destroyed, and no additional populations have been discovered during routine ecological surveys in suitable habitat.
Additionally, most of the known B. norvegicum populations in the United States are experiencing limited to no spore production, which severely limits the species’ dispersal ability and exacerbates the problems of already small isolated populations (Hague and Welch 1951; Hill 2002; Löve and Löve 1953). Other threats to this species include physical damage from walking or climbing on exposed habitats, impoundments, erosion, heat, and drying. Given its relatively recent discovery in Iowa, there is hope that a remnant population will be found in Minnesota. A targeted survey of potential habitat is warranted during non-drought years. Bryoxiphium norvegicum was originally listed as special concern in 1984, but given this species’ extreme rarity, its restrictive habitat requirements, documented habitat loss, and perceived global threats due to climate change, its status was elevated to endangered in 2013.
Bryoxiphium norvegicum is a perennial moss, usually bright-green and shiny, though occasionally light green to brownish-green (Hill 2002). Plants are slender, 8-25 mm (0.3-1.0 in.) in length, linear, and erect. The leaves (1-2 mm [0.04-0.08 in.] long), are crowded and overlapping. It is one of the few mosses where the leaves are arranged on a single plane (distichous), with two straight rows of leaves on opposite sides of the stem, resembling species of the genus Fissidens. However, B. norvegicum leaves are simple and much more elongate in well-developed plants, looking much like blades of grass. Stems are unbranched and grow attached to vertical sandstone. Sporophytes are rare, but sex organs are frequently seen (Hague and Welch 1951; Pursell 2007).
A porous substratum, capable of holding water, could be a significant ecological requirement for B. norvegicum (Löve and Löve 1953). Crum and Anderson (1981) and Pursell (2007) describe the species' habitat as "…moist, shaded sandstone, sometimes calcareous in nature (or rarely gneiss)”. Throughout its range in the United States, B. norvegicum has typically been documented on moist, shaded sandstone ledges or cliffs, particularly on the undersurfaces of ledges, sometimes overhanging water and, less frequently, on bluffs and boulders of conglomerate, gneiss, and quartzite, soil, and overturned tree bases (Crum and Anderson 1981), typically where the air is normally still and very humid. The plants are rarely, if ever, exposed to direct sunlight, at least at mid-day. Holzinger described the original Minnesota collection in The Blufflands as occurring on a "…shaded, moist sand ledge" at the entrance of a cave. This habitat would likely be classified as either southern mesic cliff or southern wet cliff. Other bryophyte species (all rare) that might potentially be associated with B. norvegicum include Schistostega pennata (luminous moss) and Seligeria species.
Biology / Life History
Unfortunately, there is very little information found in the literature on the population dynamics and life history of this moss. Recent molecular dating analyses combined with ancestral area estimations suggest that the extant range of Bryoxiphium results from both the fragmentation of a formerly wider range encompassing North America and Southeast Asia about 10 million years ago, and more recent long-distance dispersal events on oceanic islands (Patiño et al. 2016).
Populations of B. norvegicum in Iceland, Greenland, and Japan appear to reproduce regularly and successfully by means of spores, with colonies appearing as large mats (Noguchi 1987; Hill 2002). However, nearly all populations known in the United States appear to be infertile, albeit one population from Wisconsin that was documented with mature spores (Hill 2002). One of the reasons for this apparent infertility is the fact that populations are typically composed of a single sex, usually female archegonia, and thus fruiting specimens are exceedingly rare (Hague and Welch 1951). This limited data suggests that, in its current distribution in the United States, nearly all B. norvegicum reproduction, if any, is vegetative (Hill 2002).
Conservation / Management
Most of the known B. norvegicum populations in the United States are experiencing limited to no spore production, which severely limits the species' dispersal ability and exacerbates the problems of already small isolated populations (Hill 2002). As such, B. norvegicum is a prime candidate for extinction throughout its entire range due to climate change. Loss of moist, shaded microsite conditions would decimate this species, as it appears unable to stand much heat or drying. This is to be expected, considering the species generally prefers northern aspects or high elevation (Hill 2002).
Bryoxiphium norvegicum appears to be extirpated in Minnesota at the original site, either by over-collection at the turn of the previous century or by habitat destruction (Janssens 2007). There is hope that a remnant population will eventually be discovered elsewhere in Minnesota, and surveys of potential habitat are warranted during non-drought years. In other states, threats to this species have included physical damage from walking or climbing on exposed habitats, impoundments, erosion, heat, and drying.
Best Time to Search
The best time to search for B. norvegicum is from May through September or essentially anytime the ground is not covered by snow and where suitable habitats are known to occur, such as areas that are shaded and comprised of wet sandstone cliffs.
Conservation Efforts in Minnesota
Because B. norvegicum has not yet been relocated in Minnesota; no conservation efforts to protect this species have been undertaken.