Aulacomnium androgynum (Hedw.) Schwaegr.
Bud-headed Thread Moss
Basis for Listing
Aulacomnium androgynum (bud-headed thread moss) has a disjunct global distribution in the temperate bioclimatic zone, including western North America, scattered portions of eastern North America, and eastern Asia, Europe, and Patagonia. It has been recorded regionally from Ontario, Wisconsin, and the Upper Peninsula of Michigan. In Minnesota, three populations have been found in Cook County on the Susie Islands (North Shore Highlands Subsection). With so few populations documented in Minnesota, there is too little information available to detect a statewide population trend at this time. Based on its apparent rarity, Aulacomnium androgynum was designated of special concern in 2013.
Aulacomnium androgynum is erect and small in stature (1-2 cm [0.4-0.8 in.]), usually growing as basal tufts or cushions. The species is dark-green to brownish-green in color, with red-brown rhizoids appearing between the leaves near the base of the plants. The lower leaves are typically small and widely spaced, becoming more crowded towards the apex. The oblong-lanceolate leaves are widest above the rounded base, are somewhat concave to keeled, and are narrowly revolute (curved or curled back) to approximately mid-leaf. Margins are weakly serrulate (minute sharp forward-pointing teeth) near the base of the leaf and irregularly so towards the apex. The costa is slightly bent or twisted, ending somewhat below the apex. The spherical gemmae-bearing structures are a distinguishing feature of this species and are often present at the end of a naked and elongated pseudopodia (extension of a stem-tip, bearing clusters of gemmae). This type of gemmae (small cylindrical bodies, serving in vegetative reproduction) placement is extremely rare among mosses. Male plants are somewhat smaller than female.
Across this species’ range, A. androgynum occurs on organic soil, rotting logs, or mineral soil over rock in a variety of plant communities. Generally, this moss occurs in sedge meadows, treed fens, and conifer forests as a colonist. In Europe, it is often found on charred stumps in disturbed conifer forests. In Minnesota, it has only been found in conifer swamps in the northeast, such as northern rich spruce swamps (basin). However, its range could certainly extend west into larger peatland systems that exist in north-central Minnesota, including communities such as northern rich spruce swamp (water track), northern cedar swamp or northern rich tamarack swamp (eastern basin).
Biology / Life History
According to Crum (1981), the specific epithet was misapplied by Linnaeus, as it suggests that this species is monoicous (a species that bears both sperm and eggs on the same gametophyte), when in fact it is dioicous. This species is most likely to be confused with its much more common relative A. palustre. It is also possible to confuse the gemmaphore of A. androgynum with the splash-cup placement of gemmae in Tetraphis pellucida (tetraphis moss). The latter species may appear to have a spherical terminal cluster of gemmae, but that cluster is more cup-like and is surrounded by modified broad leaves, and its stalk is not completely naked of leaves. Ants could play a role as a passive vector for dispersing asexual propagules (gemmae) of A. androgynum, as gemmae have been shown to easily adhere to ants as they move over the species’ tufts (Rudolphi 2009).
Conservation / Management
Although not much is known about this species’ preferred habitat in Minnesota, existing observations indicate that it prefers conifer swamps. As such, this would indicate it prefers moist climates and microsites, and any change in the moisture regime due to climate change, disturbance, or a change in groundwater availability could impact this species.
Best Time to Search
The best time to search for Aulacomnium androgynum is from May through September or essentially anytime the ground is not covered by snow.
Conservation Efforts in Minnesota
The lone site for A. androgynum in Minnesota is on Susie Island in Lake Superior, which is now owned by the Grand Portage Band of Lake Superior Chippewa. Under band control, "human influence on the island will be kept to a minimum in order to protect areas of cultural significance as well as the natural environment".
Erika R. Rowe (MNDNR), 2018
(Note: all content ©MNDNR)