Racomitrium microcarpon (Hedw.) Brid.


Synonym: Bucklandiella microcarpa (Hedw.) Bednarek-Ochyra & Ochyra

Special status: NONE

Recognition: One of the pilose racomitriums confidently identified by microscope examination only. The basal marginal cells are elongate and esinuose, the pellucid cells extending up the border for about 15 cells. In regional material I've examinded these cells tend to be thicker walled than Racomitrium varium, the nearest look-alike that shares the basal marginal pellucid border. Other close species of Racomitrium either lack a pellucid border or the lowermost cells of this border are not elongated (as sometimes in Racomitrium macounii or Racomitrium sudeticum, both of which have bistratose margins distally). The differentiation from Racomitrium varium is readily seen in the leaf sections: this species has a thinner costa, only 2-3 cells thick near leaf base vs. average 3-4 cells thick in Racomitrium varium, and the leaf cells are strongly pseudopapillose, with high, rounded bumps over the vertical walls vs. the low, flat bumps in Racomitrium varium. The basal cells between margin and costa have very thick longitudinal walls in Racomitrium microcarpon, almost as thick as the lumens are wide, while in Racomitrium varium the same cells have walls that are only about half as thick as the cell lumens.

Distribution: Circumboreal at high latitudes, more common northwards; not yet in Oregon but reported from California in Norris & Shevock (2004a).

Comments: In the Flora North America (Ochyra & Bedkarek-Ochyra 2007) the distribution map does not show Racomitrium microcarpon located south of Washington or Montana. No Idaho record is noted in the FNA map, either, but there is a specimen from Kootenai County in the University of Washington Herbarium (Leiberg, June 1890; det. verif. Frisvoll). I have never seen this in the field; I know it only from herbarium specimens. Bedkarek-Ochyra (1995) writes, "..unlikely to be mistaken for any other. Its markedly flexuose hyaline hairpoints and strong branching with numerous tuft-like horizontal lateral branches enable it to be recognized even with the naked-eye in the field." This description fits Racomitrium varium equally well, especially the shoots that creep across a rock face. Only the presence or absence of alternating stem sectors of muticous and pilose leaves is likely to be a useful character to distinguish these in the field.

The Leiberg specimen photographed here is the same one described and figured by Lawton (1972) from the University of Washington Herbarium.

Kootenai Co., Idaho. J.B. Leiberg, June 1890 (WTU).

Racomitrium microcarpon; Kootenai Co., Idaho. J.B. Leiberg, June 1890 (WTU). Note: thumbnail is only a portion of the entire image.

Racomitrium microcarpon; Kootenai Co., Idaho. J.B. Leiberg, June 1890 (WTU).

Racomitrium microcarpon; Kootenai Co., Idaho. J.B. Leiberg, June 1890 (WTU).


Guide to Racomitrium of Oregon
Created 2007 Northwest Botanical Institute