Bull. Natl. Mus. Nat. Sci., Ser. B, 47(1), pp. 37–39, Frbruary 22, 2021

Plagiothecium argentatum (Plagiotheciaceae, Bryophyta)
New to Myanmar
Masanobu Higuchi1,* and Mu Mu Aung2
1

Department of Botany, National Museum of Nature and Science, 4–1–1 Amakubo, Tsukuba, Ibaraki
305–0005, Japan
2
Forest Research Institute, Forest Department,
Ministry of Natural Resources and Environmental
Conservation, Yezin, Nay Pyi Taw, Myanmar*E-mail: higuchi@kahaku.go.jp(Received 30 November 2020; accepted 23 December 2020)

Abstract Plagiothecium argentatum (Mitt.) Q.Zuo, known from India, Nepal, Bhutan and China,
is reported as new to Myanmar. The description and illustration based on Myanmar plants aregiven. This species is characterized by the absence of caducous leaves and naked shoots, serrate
leaves and elongate laminal cells. The diﬀerentiation of epidermal cells of stem is noted.
Key words : bryophytes, epidermal cells of stem, Himalayan element, Myanmar, Plagiothecium.

Plagiothecium argentatum (Mitt.) Q.Zuo has
been treated as Struckia argentata (Mitt.) Müll.
Hal. for a long time. Struckia is small Asian
genus including at most two species, S. enervis(Broth.) Ignatov, T.J.Kop & D.G.Long and S.
zerovii (Lazarenko) Hedenäs except S. argentata.
The taxonomic position of Struckia has been discussed by several authors (Tan et al., 1990;
Hedenäs, 1996; Ignatov et al., 2007). Zuo et al.
(2011) proposed that Struckia was reduced to asynonym of Plagiothecium based on a phylogenetic analysis using multiple nuclear and chloroplast regions.
In November 2017, the ﬁrst author collected asmall moss growing on tree-trunk in Chin Hills,Myanmar. Through a close examination we conﬁrmed that the plants are Plagiothecium argentatum (Mitt.) Q.Zuo which is the ﬁfth species ofthe genus in Myanmar, where four species ofPlagiothecium, P. neckeroideum, P. nemorale, P.
paleaceum and P. svihlae, have been reported(Tanaka et al., 2003).

© 2021 National Museum of Nature and Science

Plagiothecium argentatum (Mitt.) Q.Zuo, J.
Bryol. 33: 27. 2011.
[Fig. 1].
The following description is based on theMyanmar plants.
Plants small for the genus, in sparse, palegreen to yellowish green, usually glossy mats.
Stems creeping, sympodial, radiculose on primary stems, irregularly branching; secondary
stems ascending; cross-sections of creeping
stems round, 130–150 μm in diameter; central
strand slightly diﬀerentiated; epidermal cells
hyaline, with thin outer walls. Pseudoparaphyllia
lacking. Rhizoids originating in a cluster fromthe abaxial leaf costa insertion or from basal rowof abaxial stem leaf cells. Branches erect, julaceous, up to 10 mm long, 1.6–3.0 mm wide,
including leaves when moist. Leaves of creeping
primary stems erect to erect-patent, sparsely foliated or imbricate, triangular, gradually narrowed
to a piliferous acumen, 0.4–0.7 mm long, 0.15–0.2 mm wide. Leaves of ascending secondary
stems crowded, imbricate when dry, spreadingwhen moist, almost symmetrical, ovate oroblong-ovate, abruptly acute, 1.7–2.0 mm long,38

Masanobu Higuchi and Mu Mu Aung

Fig. 1. Plagiothecium argentatum (Mitt.) Q.Zuo A. Plants showing creeping primary stems and ascending secondary stems and erect branches. B. Rhizoids originating in a cluster from the abaxial leaf costa insertion. C.
Transverse section of primary stem. D. Transverse section of secondary stem. E. Stem leaf of primary stem. FStem leaf of secondary stem. G. Apical part of stem leaf of secondary stem. H. Median cells of stem leaf ofsecondary stem. I. Alar cells of stem leaf of secondary stem. Scales: A & F = 1 mm, B–D & G–I = 100 μm, E =0.25 mm, F = 1 mm. All from Higuchi 56477 (TNS).

0.6–0.8 mm wide, concave, not plicate; margins
plane, entire throughout or with some weak serrations at apex; base not decurrent; alar cells
quadrate or rectangular; costa thin, forked andshort; median laminal cells narrow, linear-ﬂex-

uose,
smooth,90–120(–140) μmlong,10–12(–14) μm wide, thin-walled. Branch leaves
similar to the leaves of ascending secondary
stems, sometimes smaller than them. Sexualorgans and sporophytes not seen.

Plagiothecium argentatum new to Myanmar

Specimens examined. Myanmar. Chin State,Chin Hills, Mindat Township, northwest of town,
2520 m alt., on tree-trunk in Quercus forest atridge, November 28, 2017, coll. M. Higuchi
56473, 56477 (RAF, TNS).
Distribution. India, Nepal, Bhutan and China(cf. Tan et al., 1990). New to Myanmar.
Plagiothecium argentatum is characterized by
the absence of caducous leaves and naked shoots,
serrate leaves (Fig. 1G) and elongate laminal
cells (Fig. 1H). This species has been known
from the Himalayan region of India, Nepal, Bhutan and China (cf. Tan et al., 1990). In Myanmar,
this species grows on tree-trunk in Quercus forest at ridge of higher elevation, being mixed withBrachymenium nepalense. Plagiothecium argentatum is one of the Himalayan element in themoss ﬂora of Myanmar.
Hedenäs (1996) examined the detail morphological features of the genus Struckia based on
the specimens which are kept in the herbaria of
the New York Botanical Garden (NY) and theNatural History Museum of Stockholm (S). He
described the stem structure of the genus, “Stemwith central strand, and cortex (including epidermis) of 1–2 layers of small and slightly incrassate cells.” In Myanmar plants of Plagiotheciumargentatum, the secondary stems with larger
leaves do not show any diﬀerentiation of epidermal cells (Fig. 1D). The primary stems, however,show distinct diﬀerentiation of epidermal cells,
that is, they are hyaline, with thin outer walls(Fig. 1C). This is one of the common characteristics of the family Plagiotheciaceae.

39

Acknowledgments
We wish to express our sincere thanks to Forest Research Institute, Myanmar, and the members of the ﬁeld research in November, 2017, fortheir kind help in the ﬁeld research. This study
was carried out by the international cooperative
project “Biological Inventory with special attention to Myanmar” as the integrated research initiated by the National Museum of Nature and Science, Japan based on a memorandum ofunderstanding (MoU) with the Forest Department, Ministry of Natural Resources and Environmental Conservation, Myanmar.
References
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