Fissidens closteri

Fedosov, V. E., Wei, Y., Ho, BC., Atwood, J., Kuznetsova, O. I. & Ignatov, M. S., 2024, The genus Fissidens in Russia, III: Fissidens kiusiuensis (Bryophyta), new species for the Russian Far East, Arctoa 33 (2), pp. 107-116 : 114

Comparison of Fissidens closteri and F. kiusiuensis

In addition to the main morphological distinction in the mostly smooth calyptra (mammillose only near the tip) in American plants vs. a scabrous calyptra in the Asian ones, comparisons of traits of these two species, accepted as subspecies, were published by Crum & Anderson (1981) and Iwatsuki & Suzuki (1982). The former authors noted that the costa is stronger in the Asian plants, and that the leaf margin is distinctly serrate. The latter publication summarized differences of North American vs. Asian taxa by smaller leaves (0.4–0.75 vs. 0.3–0.9 mm long), leaf margin subentire vs. serrate, shorter seta (1.2 vs. 1.3–4.0 mm), and smaller spores 7–10 vs. 10– 15 µm. Iwatsuki & Suzuki (1982) did not confirm excurrent costa in Japanese plants, mentioning that by these traits the taxa are subidentical. However, the costa transverse section was found to possess many stereids, which is not the case in North American plants, nor in Asian ones observed by us.

Selected North American collections studied:

U.S.A. Missouri, Saint Genevieve County, Hickory Canyon Natural area, Benne Tract, cobble bed along small drainage leading into the south branch of Hickory Creek, 37°52’18’’N 090°18’30’’W, 807 ft. On top of a 6 inch piece of shaded, dry cobble, with Hypnum cupressiforme and Fissidens bryoides , 12 Oct 2019 Atwood 3768 (MO, dupl. MHA).

Iwatsuki & Suzuki (1982) mentioned that the North American plants have scabrous calyptrae, which disagrees with the descriptions in Crum & Anderson (1981) and Pursell (2007), as well as lectotype and several syntype specimens of the species (FH, NY, BM001094038!), and high-quality photomicrographs depicting Alabama, Mississippi and North Carolina specimens of F. closteri taken by Paul Davison at the University of North Alabama:

https://www.southernappalachianbryophytes.org/ fissidensclosteri.html

Fissidens kiusiuensis is indeed a variable species. The shorter leaves are roughly crenulate ( Figs. 4K , 5E), whereas some longer ones are attenuate ( Figs. 4J , 5F), and then in the distal half have the margin subentire. A similarly subentire upper leaf margin has been mentioned for this species recently by Kwon (2021) for Korean plants.

Figures

Fig. 4. Fissidens kiusiuensis from Russia, Fedosov et al., MHA9131858 (A–B, D–M), and F. closteri from USA, Atwood, MO 3768 (C). A–C: peristomes; D: Capsule, still operculate; E–G, I, K: habit of plants with young sporophytes, still covered by calyptrae; H: calyptra with scabrous surface, close up of G; J: leaf from plant in ‘I’, distally attenuate; L–M: leaves, showing variation, cf. also ‘J’ and ‘K’ for the leaf margin serration.