Thelia hirtella (Hedw.) Sull. in Sull. & Lesq.
Basis for Listing
Thelia hirtella (nipple moss) is endemic to eastern North America, within the temperate bioclimatic zone. It has been recorded regionally from Ontario, Nebraska, Iowa, and Wisconsin. In Minnesota, only two populations have been discovered in St. Louis County in 1976 (Northern Superior Uplands). With so few populations documented in Minnesota, there is too little information available at this time to detect a statewide population trend (Janssens 2005). Further inventory work is needed to clarify the species’ distribution in the state as well as potential threats to its survival. Based on its apparent rarity, Thelia hirtella was designated a species of special concern in 2013.
Thelia hirtella is a small plant that creeps up the base of trees, sometimes to a height of 60 cm (2 ft.), forming mats that are pale green to grayish green. The long trailing brown-felted stems are sparsely and irregularly pinnate; branches are spreading or erect and abundantly covered in paraphyllia (brown or green thread-like hairs or fuzz) that attach the plants to bark. Stem leaves are distinctly larger than branch leaves, 1.0-1.3 mm (0.04-0.05 in.) long, and strongly ciliate along the margins (Crum and Anderson 1981). Branch leaves are only 1.0 mm (0.04 in.) long, cupped and scale-like, deltoid-ovate and narrowed to a short to fairly long apiculus (abruptly short-pointed), and appearing julaceous (smoothly cylindrical). Teeth along the margins are irregularly dentate and are difficult to see (McKnight et al. 2013). The costa (midrib) is single, 1/2-3/4 the length of the leaf and is often indiscernible, even with a hand lens (Crum and Anderson 1981; McKnight et al. 2013). Setae (stalks) are 5-12 mm (0.2-0.7 in.) long, supporting a capsule that is upright, cylindrical, and about 2 mm (0.08 in.) long. Thelia asprella (thelia moss) is a similar species that also grows on trees, except its stem and branch leaves are not as differentiated, and it has less paraphyllia than T. hirtella.
Thelia hirtella frequently grows on bark at the base or on the trunks of hardwoods, sometimes on decayed logs and stumps, rarely on soil or rock.
Biology / Life History
Separate male and female plants, with dwarf male plants resting on the leaves of the larger female plants; however, male plants are few and hard to find (Crum and Anderson 1981). The specific epithet, meaning hairy, refers to the ciliate leaf margins.
Conservation / Management
Very little is known about this moss species other than its preferred habitat on the bark of hardwoods. The most obvious threat to this species is any activity where a significant amount of trees that serve as substrate for T. hirtella would be removed.
Best Time to Search
The best time to search for Thelia hirtella is from May through September or essentially anytime the ground is not covered by snow, since this species typically occurs at, or near, the base of trees.
Erika R. Rowe (MNDNR), 2018
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