Rusty Beard-moss

Didymodon ferrugineus (Schimp. ex Besch.) M.O. Hill

Didymodon ferrugineus
Michael Luth

State Protection
Not Listed
Not listed or protected by New York State.
Federal Protection
Not Listed
State Conservation Status Rank
Critically Imperiled or Imperiled in New York - Especially or very vulnerable to disappearing from New York due to rarity or other factors; typically 20 or fewer populations or locations in New York, very few individuals, very restricted range, few remaining acres (or miles of stream), and/or steep declines. More information is needed to assign either S1 or S2.
Global Conservation Status Rank
Secure globally - Common in the world; widespread and abundant (but may be rare in some parts of its range).


Did you know?

Dr. Richard Zander, former curator of the Clinton Herbarium in Buffalo, used this moss to experiment with the change in color of moss leaves exposed to acids and bases. The acid-base color reaction is one of the only ways to distinguish this moss from the very similar moss Triquetriella californica (Zander 1980).

State Ranking Justification

The rank is designated based on Cleavitt et al.'s (2006) report. Four specimens were verified. The last collection was made in 2005.

Short-term Trends

The short term trend is unknown. Four verified sites were documented in 2005 but counts were not available from these surveys. No subsequent visits have been made to confirm the stability of these populations

Long-term Trends

The long term trend appears positive there are four extant sites and no sites have been documented as lost or historical in New York.

Conservation and Management


Over collection and human disturbance to plants growing on accessible cliff faces and talus slopes could be threats.

Conservation Strategies and Management Practices

Montior the impact of visitation and human disturbance to populations on accessible cliff faces and talus slopes.

Research Needs

The collection and analysis of specific microhabitat data for the immediate areas where these mosses are growing would aid in developing a better understanding of its habitat. Surveys documenting the nonvascular and vascular plant species growing in immediate association with this species in New York are needed.



In New York this species has been collected from ledges, cliffs, and talus slopes associated with limestone (NYNHP 2012). Wet, calcareous soil, rock outcrops, ledges (including concrete walls) (FNA 2007b).

Associated Ecological Communities

  • Alvar woodland* (guide)
    A subset of the limestone woodland community restricted to the alvar region in Jefferson County, New York.
  • Calcareous cliff community (guide)
    A community that occurs on vertical exposures of resistant, calcareous bedrock (such as limestone or dolomite) or consolidated material; these cliffs often include ledges and small areas of talus.
  • Calcareous shoreline outcrop* (guide)
    A community that occurs along the shores of lakes and streams on outcrops of calcareous rocks such as limestone and dolomite. The vegetation is sparse; most plants are rooted in rock crevices.
  • Calcareous talus slope woodland (guide)
    An open or closed canopy community that occurs on talus slopes composed of calcareous bedrock such as limestone or dolomite. The soils are usually moist and loamy; there may be numerous rock outcrops.
  • Limestone woodland* (guide)
    A woodland that occurs on shallow soils over limestone bedrock in non-alvar settings, and usually includes numerous rock outcrops. There are usually several codominant trees, although one species may become dominant in any one stand.

* probable association but not confirmed.


New York State Distribution

In New York, this moss has been found at disjunct upstate locations in Erie, Madison, and Tompkins counties.

Global Distribution

Rusty beard-moss has a global distribution in the northern hemisphere ranging from Central America, Mexico and the West Indies to Africa, Europe, Asia and north Africa to Greenland and Canada aside from Prince Edward Island, Quebec, Saskatchewan and Nova Scotia. In the United States it is primarily a northern species occuring in Alaska, Vermont, New York, Michigan, Montana, Colorado Illinois, New Mexico, North Carolina, Virginia, West Virginia and Arkansas.

Identification Comments

Identifying Characteristics

Didymodon ferrugineous grows in patches or loose tufts with stems reaching up to 2.5 cm in length. It usually has red-brown shoots tipped with green. The stem leaves vary from appressed to spreading when dry, but are strongly recurved and keeled when moist. They show little or no variation in morphology (monomorphic), are egg-shaped -triangular to -lanceolate, grooved along the midrib (costa) on their upper surface (adaxially), and 0.8--2 mm long. The leaf bases are scarcely differentiated in shape to egg-shaped, margins nearly flat (plane) to recurved at midleaf, usually entire, with a broadly acute but not fragile tip. The costa extends to or slightly beyond the leaf tip (percurrent to short-excurrent), is weakly tapering and not much wider at the base, costal cells are elongate on the upper leaf surface, 2 to 4 cells wide at midleaf, guide cells in 1 layer; basal leaf (laminal) cells little differentiated, quadrate or very short-rectangular, walls thickened; laminal cells 11 to 15 µm wide, roughly square, papillae usually present, simple, often large and sharp with 1 to 3 centered over angular lumens, lumens that have irregularly thickened walls that are convex on both sides and 1 layered. The capsule is 0.7 to 1.5 mm long and borne on a 0.6 to 1.2 cm long stalk (seta). The inside the capsule mouth bears a fragile circle of 16 tiny (275 to 600 µm), linear teeth (peristome), that are cleft to near the base, and nearly straight to twisted counterclockwise once. These may often appear missing. The spores are 7 to 9 µm in diameter.

Best Life Stage for Proper Identification

This species may be identified from vegetative material (the gametophyte stage).

Similar Species

Didymodon ferrugineus can be distinguished from the other New York species, D rigidulus var. rigidulus, by its the strongly recurved and keeled moist leaves and absence of gemmae in its leaf axils. D. rigidulus typically has axillary gemmae and it leafs are only spreading when moist. Barbula spp can also be distinguished by the presence of axillary gemmae, and typically very papillose, blunt leaves. In contrast, D. ferrugineus' leaves are weakly papillose, broadly acute and lack axillary gemmae. Gymnostomum aeruginosum plants are light to dark green and lack a ring of teeth (peristome) inside the capsule mouth, while D. ferrugineus is usually red-brown with green tips and its capsule has a well developed peristome bearing 16 teeth.

Best Time to See

The gametophyte (vegetative) form of this moss may be seen throughout the year. The sporophyte (reproductive) form of this moss is rare, when present capsules mature winter-spring. For positive identification a small piece of the plant including the entire stem, with leaves and intact capsules (if present) is ideal. The species can generally be identified in vegetative condition using the stem and leaf characters.

  • Vegetative
  • Fruiting

The time of year you would expect to find Rusty Beard-moss vegetative and fruiting in New York.

Rusty Beard-moss Images


Rusty Beard-moss
Didymodon ferrugineus (Schimp. ex Besch.) M.O. Hill

  • Kingdom Plantae
    • Phylum Bryophyta
      • Class Bryopsida
        • Order Pottiales
          • Family Pottiaceae


  • Barbula reflexa (Brid.) Brid.
  • Didymodon fallax var. reflexus (Brid.) Zand.

Additional Resources


Anderson, L.E., H.A. Crum, and W.R. Buck. 1990. List of the mosses of North America north of Mexico. The Bryologist 93(4):448-499.

Cleavitt, N.L., S.A. Williams, and N. Slack. 2006. Updating the rare moss list for New York State: Ecological community and species-centered approaches. Final report for the Biodiversity Research Institute. New York State Museum. Albany, NY.

Flora of North America Editorial Committee. 2007b. Flora of North America North of Mexico. Vol. 27. Bryophytes: Mosses, Part 1. Oxford University Press, New York. xxi + 713 pp.

New York Natural Heritage Program. 2024. New York Natural Heritage Program Databases. Albany, NY.

Zander, Richard. 1980. Acid-Base Color Reactions: The Status of Triquetrella ferruginea, Barbula inaequalifolia and B. calcarea. The Bryologist 83(2): 228-233.


About This Guide

Information for this guide was last updated on: January 8, 2016

Please cite this page as:
New York Natural Heritage Program. 2024. Online Conservation Guide for Didymodon ferrugineus. Available from: Accessed April 17, 2024.