Fissidens dubius
Fissidens arcticus
fissidens moss
arctic fissidens moss
usually branched;
axillary hyaline nodules absent;
central strand present.
usually unbranched;
axillary hyaline nodules absent;
central strand weak.
as many as 25 pairs, often undulate, oblong to lanceolate, obtuse to acute, often apiculate, to 3.5 × 0.7 mm;
dorsal lamina truncate-rounded proximally, ending at insertion, not decurrent;
vaginant laminae 2/3 the leaf length, ± unequal, minor lamina ending near margin;
margin crenulate to crenulate-serrulate but unevenly serrate at leaf apex, elimbate;
costa ending a few cells before apex to percurrent, taxifolius-type;
laminal cells irregularly 2-stratose in dorsal and ventral laminae, ± obscure, smooth, bulging, firm-walled, rounded-hexagonal, 7–10 µm, 3–4 rows of marginal cells thinner, walls slightly thicker, forming a pale marginal band.
as many as 40 pairs, lanceolate to oblong-lanceolate, generally broadly acute, 0.4–1.5 × 0.2–0.3 mm;
dorsal laminae narrowed proximally, often ending well before insertion;
vaginant laminae 1/2–3/4 leaf length, ± equal, minor lamina ending on or near margin;
margin entire but often ± serrate distally, limbate on the vaginant laminae, infrequently limbate on dorsal and ventral laminae of perichaetial leaves, limbidial cells 1-stratose;
costa usually ending 2–3 cells before apex, bryoides-type;
laminal cells 1-stratose, distinct, smooth, slightly bulging, firm-walled, irregularly quadrate to hexagonal, 8–11 µm. Sexual condition polyoicous, most frequently gonioautoicous;
naked antheridia often in axils of distal leaves.
to 11 mm.
1.75–6 mm.
dioicous;
perigonia on short axillary branches and elongate stems;
perichaetia on short axillary branches, mostly near proximal ends of stems.
theca slightly inclined, slightly arcuate, bilaterally symmetric, to 1.8 mm;
peristome taxifolius-type;
operculum 1–1.4 mm.
theca exserted, usually erect, radially symmetric, 0.4–0.8 mm;
peristome bryoides-type;
operculum 0.6 mm.
cucullate, smooth, 1.8 mm.
not seen.
13–20 µm.
14–20 µm.
1 per perchaetium.
1 per perichaetium.
Fissidens dubius
Fissidens arcticus
In contrast to Fissidens adianthoides, F. dubius has smaller, irregularly 2-stratose, obscure laminal cells. Subterranean, irregularly globose, multicellular rhizoidal gemmae have been reported for F. dubius as well as F. osmundioides and F. taxifolius in Europe and Japan. Z. Iwatsuki and T. Suzuki (1982) cited the occurrence of dwarf male plants (small perigonial stems located on the leaves of perichaetial plants) in Japanese specimens.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Differing opinions have been expressed on the taxonomic standing of Fissidens arcticus. According to W. C. Steere (1978), it might be only an environmentally induced expression of F. bryoides, but A. A. Frisvoll (1981), who reported the species from Svalbard, suggested that it be treated as a subspecies or variety of F. bryoides. They and other previous workers (Steere and G. R. Brassard 1974; M. A. Bruggeman-Nannenga and E. Nyholm 1986), however, did not mention the dimorphic stems, of which the fertile (perichaetial) ones are shorter and have fewer pairs of leaves than the infertile ones. That character and the tendency of the limbidium to be expressed on all laminae of the leaves of perichaetial stems but otherwise restricted to the vaginant lamina of infertile stems distinguish F. arcticus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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