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COSEWIC Assessment and Status Report on the Columbian Carpet Moss in Canada

COSEWIC Status Report
on the
Columbian Carpet Moss
Bryoerythrophyllum columbianum
in Canada

Species Information

Name and Classification

Scientific Name:
Bryoerythrophyllum columbianum (Herm. & Lawt.) Zand.
Pertinent Synonyms:
Didymodon columbianus Herm. & Lawt.
Common Name:
Columbian Carpet Moss
Major Plant Group:
Mosses (Musci)

The Pottiaceae is a large and diverse family of mosses with many of its species restricted to dry environments. It is a taxonomically difficult family and has been undergoing extensive review in recent times (Zander 1993). New genera have been created or the constraints of older genera have been changed to exclude some species and/or include others from different genera. One result is that a number of taxa formerly members of either Barbula or Didymodon have been placed into Bryoerythrophyllum, including Bryoerythrophyllum columbianum (Zander 1978), following its initial description as a species of Didymodon (Hermann & Lawton 1968). Bryoerythrophyllum consists of a group of species characterized by turf-forming to loosely caespitose plants, sometimes with red to reddish-brown colouration on older parts, crowded upper laminal papillae (wart-like bumps over the leaf surface) that often obscure the cells, and strongly differentiated basal leaf cells (Chen 1941, Zander 1993, 2002).

According to Zander (2000), there are three additional species of Bryoerythrophyllum in North America: B. ferruginascens (Stirt.) Giac., B. inaequalifolium (Tayl.) Zand., and B. recurvirostrum (Hedw.) Chen. Anderson et al. (1990) also reported B. recurvum (Griff.) Saito from North America, but this has been transferred to Bellibarbula as B. recurva (Griff.) Zand. (Zander 1993). Zander (2000) lists B. columbianum and B. recurvirostrum from Canada, and noted that B. ferruginascens has been reported from Newfoundland (R. Zander pers. comm. 2002). He suspects that B. inaequalifolium is present in Canada as well. Ireland et al. (1987) reported that Bjamesonii (Tayl.) Crum and, possibly, B. alpigenum (Vent.) Chen are also present in Canada, but Zander considers these species to be large forms of B. recurvirostrum.

Bryoerythrophyllum columbianum is distinguished from other species in the genus principally by leaf characteristics:

  1. its leaves end in sharp mucros consisting of elongate cells,
  2. rows of smooth cells are sometimes present along the distal leaf margins, and
  3. the costa, or leaf mid-rib, of B. columbianum is much wider at midleaf, and its upper surface bulges as a unistratose pad of cells.


The following description has been derived from Zander (1993, 2000), Lawton (1971), McIntosh & Paige (2001), and from examination of herbarium specimens. Figure 1 is a composite illustration from Zander (2000) and shows many of the features discussed below.

Figure 1: Illustration of Plant, Leaves, and Cell Details of B. columbianum from the Bryophyte Flora of North America Project

Figure 1: Illustration of plant, leaves, and cell details of B. columbianum from the Bryophyte Flora of North America project.

Upper left is stem cross-section, center is leaf tip and cross-section near middle of leaf.

Bryoerythrophyllum columbianum is a perennial, acrocarpous (producing female structures and sporophytes at the tips of the main stems) moss species that grows in small clumps or compact turfs either as pure colonies or intermixed with other mosses and lichens. Stems branch at the base, and range from 2–6 mm in height, although smaller plants are common in provincial collections (1–3 mm stems are common in British Columbian collections). The leaves of B. columbianum are ovate-lanceolate to, less commonly, ovate, and usually sharply acute. They are stiffly erect to, rarely, twisted in some larger plants, imbricate (overlapping), and usually dark red-brown when dry, and erect-spreading, and sometimes green, when wet. Leaves range from 0.8–1.2 mm in length, although Zander (2000) notes that they can be somewhat longer. Leaf margins are entire and narrowly recurved from near the base almost to the apex.

The leaf midrib is up to 8 cells wide at midleaf, and the upper surface bulges forming a distinctive pad. The midrib is excurrent, forming a sharp mucro comprised of elongate cells, at least on the younger leaves. In older and eroded leaves, this apical cell is difficult to see or is absent, making species confirmation difficult in some specimens. The median and upper leaf cells of Bryoerythrophyllum columbianum are isodiametric to irregular-short-rectangular, are covered by small papillae, and range in size from 8–15 µm in diameter. The basal cells are smooth, thin-walled, and quadrate to short-rectangular.

Bryoerythrophyllum columbianum is dioicous, with male and female organs on separate stems. Leaves around the female sex organs are larger and more concave than the stem leaves, ranging from 1.6–1.8 mm in length, and often have plane margins. Sporophytes, which produce spores, mature in early spring, but are rarely found across its North American range. Its capsules (spore producing sacs) are long-exserted above the leaves on a dark seta (stem), and are cylindrical to ovate-cylindrical. They have conic-rostrate opercula (lids) and their peristomes, fringes of tooth-like appendages surrounding the mouth of the capsule, are rudimentary or absent. Its nearly smooth spores range in size from 8–13 µm.

In British Columbia, Bryoerythrophyllum columbianum can be confused with Didymodon vinealis (Brid.) Zand., a more common moss of similar habitats which also grows as red-brown patches over soil. This species can be distinguished from B. columbianum by its less recurved and, usually, more twisted upper leaves, at least when dry, its much narrower leaf mid-ribs, and the absence of a multi-cellular and sharply pointed leaf apex, although it does have a smaller and blunter conical cell at the leaf apex. Tortula atrovirens (Sm.) Lindb., formerly Desmatodon convolutus (Brid.) Grout, another red-brown and small taxon that is relatively common in silt-rich sites in the province, can also be confused with B. columbianum. It is distinguished from B. columbianum by its blunt leaf apices and generally tightly twisted habit when dry.

Taxonomic keys and additional illustrations are found in Lawton (1971, as Didymodon columbianus) and Zander (1978, 2000).