Bull. Natl. Mus. Nat. Sci., Ser. B, 42(1), pp. 19–23, February 22, 2016

A New Locality of Fossombronia mylioides(Fossombroniaceae, Marchantiophyta)
Masanobu Higuchi
Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan
E-mail: higuchi@kahaku.go.jp(Received 30 November 2015; accepted 22 December 2015)

Abstract A new locality of Fossombronia mylioides is reported from Iriomote Island, southwestof Ryukyu Islands, Japan. Fossombronia mylioides has been only known from the type locality.
Morphological characteristics of the plants from the new locality are compared with those of theformer collections. Details of the spore dispersal of the species are described for the ﬁrst time.
Key words : bryophytes, Fossombronia mylioides, Japan, new locality, spore dispersal.

Fossombronia mylioides (Fossombroniaceae,Marchantiophyta) was described by Inoue (1973)
based on the specimen collected from Iriomote
Island, southwest of Ryukyu Islands, Japan. Thisspecies has been known from the type locality
along Urauchi River situated in the west of Iriomote Island. The other specimen of this species
is a 1998 collection by T. Yamaguchi from thetype locality distributed as no. 142 in Fasc. 6 ofthe exciccatae series “Bryophytes of Asia” editedby H. Deguchi and T. Yamaguchi (HIRO). A newlocality of Fossombronia mylioides at Nakama
River situated in the east of the island was foundduring performing research of the island in 2011.
The plants with mature sporophytes enabled toobserve the process of the spore dispersal which
has never been known on the species.
Fossombronia mylioides Inoue, Journal of Hattori Botanical Laboratory 37: 296. 1973. (Figs.
1–21)
The following description is based on theplants from Nakama River in 2011.
Plants light green, medium to large for thegenus, 4–10 mm long, 2–3 mm wide. Stems dorsally compressed to slightly concave, usually

unbranched, rarely dichotomously branched.
Leaves imbricate, horizontal to patent-divergent,obliquely inserted, succubous, broadly oblong
rectangular to quadrate, 1.4–1.8 mm long ×1.6–
2.5 mm wide, plane, but somewhat undulate at
the apices, slightly lobed; margins entire or occasionally irregularly angulate. Median leaf cells
isodiametric to elongate, thin-walled, without
trigones, 60–90 μm long, 30–70 μm wide; marginal cells smaller than the median cells. Rhizoids dense, deep purple, along the ventral surface of the stem. Monoicous, antheridia andarchegonia scattered along the dorsal surface ofthe stem. Archegonia surrounded small scale-likeleaves on dorsal surface of the stem at apex. Caulocalices (＝pseudoperianths) campanulate, often
somewhat ﬂaring at mouth, usually split almost
to base on both sides.
Sporophytes matured in spring (March). Setae
2–3 mm long. Capsules spherical, deep brown,
dehisce irregularly when matured. Spores spherical, 30–46 μm in diameter; distal surface subcristate to irregularly lamellate; proximal surface
irregularly lamellate. Elaters 90–160 μm long,rarely branched, with 2 spiral thickening bands.

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Masanobu Higuchi

Figs. 1–4. Habitats of Fossombronia mylioides Inoue. 1, 2. Plants are growing on boulder covered with sandy
soil on the riverside. 3, 4. Plants are associated with Riccardia sp. Photo by M. Higuchi on March 11, 2011.

Specimens examined. Japan. Ryukyu Islands,
Iriomote Island, Okinawa Pref., Yaeyama-gun,Taketomi-cho, upper stream of Nakama River,southeast of Island, south of Mt. Gozadake,
24°17′47N, 123°49′43E, 30 m alt., March 11,
2011, coll. M. Higuchi 53855, 53856 (TNS);
Urauchi River, January 14, 1973, coll. H. Inoue
21055 (type in TNS); March 18, 1998, coll. T.
Yamaguchi, no. 142 in Fasc. 6 of the exciccatae
series “Bryophytes of Asia” (TNS).
Distribution. Endemic to Japan (IriomoteIsland).
As the epithet “mylioides” indicates, Fossombronia mylioides is much like the species ofMylia or Jungermannia in appearance (Fig. 4).
Four species of Fossombronia, F. alaskana, F.
japonica, F. mylioides and F. pusilla, are distributed in Japan (Krayesky et al., 2005; Katagiriand Furuki, 2012). F. mylioides is distinguishedfrom other species of Fossombronia by having
leaves horizontal to patent-divergent and usually
undulate with entire margins (Fig. 17), sporeswith distal surface subcristate to irregularly
lamellate (Fig. 19), elaters with 2 spiral thickenings (Fig. 20) and monoicous sexuality.
Inoue (1973) described the habitat of F. mylioides, “F. mylioides always occurs on moist
rocks or stones in river-beds; occasionally it may
be submerged during high water.” The habitat of
the new locality is similar to that of the typelocality. It grows on open boulder covered withsandy soil on the riverside, mixed with Riccardia
sp., where ﬂooding may occur (Figs. 1, 2). Inaddition, the plants are tightly attached to substrate by rhizoids.
Krayesky et al. (2005) pointed out that thesporophytes mature in March based on Yama-A New Locality of Fossombronia mylioides

21Figs. 5–16. Spore dispersal of Fossombronia mylioides Inoue. 5. Capsule with moist capsule wall. 6. Capsulewith dry capsule wall. 7–9. Capsule dehisces irregularly. 10–16. Spores and elaters are released. A fallen
spores and elaters is seen in Figs. 13–16.

guchi collection collected on March 18, 1998,
although Inoue (1973) stated that in February.
The plants at Nakama River have not only immature sporophytes but also matured ones, which
supports that the sporophytes of F. mylioides
mature in March. The spore size of 23–32 μm in
diameter by Inoue (1973) is rather smaller than
30–46 μm in the present study. Krayesky et al.
(2005) reported the spore size of 36–42 μm in
diameter based on Yamaguchi collection, andsuggested that the capsules of the type collection

were still not totally mature. Although Krayesky
et al. (2005) noted “Inoue (1973: 296) described
spores as having “very distinct reticulations,”
which is what he perceived viewing the still
immature spores with an optical microscope,”
Inoue (1973) did not describe spores as havingvery distinct reticulations. In the original description, Inoue (1973) described “spores 23–32 μm in
diam., often with narrow wing, with rather indistinct reticulation.” Probably Krayesky et al.
(2005) misunderstood with the description of F.

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Masanobu Higuchi

Figs. 17–21. Fossombronia mylioides Inoue (Higuchi 53855). 17. Leaf. Scale bar＝1 mm. 18. Scale-like leaf surrounding archegonia on dorsal stem at apex. Scale bar＝0.5 mm. 19. Spore. Scale bar＝50 μm. 20, 21. Elaters.
Scale bar＝50 μm.

foveolata Lindb. in Inoue (1973) such as “However, in F. foveolata Lindb. the spores are large(35–50 μm in diam.), with very distinct reticulations.” The leaf size and cell size of the plantsfrom Nakama River are a little larger than thoseof the type collection and Yamaguchi collection
and the shape of the caulocalyx is somewhat different among them, which may be included inthe variation. Inoue (1973) and Krayesky et al.
(2005) described that this species has small andtriangular perigonial leaves, which were notobserved on the plants from Nakama River, thatis, antheridia are naked and scattered along thedorsal surface of the stem.
One of the diagnostic characters of Fossombronia is the way of the spore dispersal, that is,the capsules dehisce irregularly when theyrelease spores. The details of the spore dispersal,
however, have never known in F. mylioides. I
observed the process of the spore dispersal in thelaboratory in April 4, 2011 (Figs. 5–16). After thematured capsules dry, they dehisce irregularly
from apex downwards (Figs. 5–7). The capsuleslack vertical lines of dehiscence. The capsulewalls break into irregular fragments by irregularsplitting (Figs. 8–12). Spores and elaters are
released with a tendency to fall as a group (Figs.
13–16). In this case, it took about 22 minutes
until the spore dispersal ends (Fig. 16) after thecapsule begins to dehisce (Fig. 7).

A New Locality of Fossombronia mylioides

Acknowledgments
I wish to express my sincere thanks to Dr. T.
Yamaguchi of Hiroshima University for his kind
help in the ﬁeld research in 2011.

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References
Inoue, H. 1973. The genus Fossombronia Raddi in Japan.
Journal of Hattori Botanical Laboratory 37: 293–297.
Katagiri, T. and Furuki, T. 2012. Checklist of Japaneseliverworts and hornworts, 2012. Bryological Research
10: 193–210 (in Japanese).
Krayesky, D. M., Crandall-Stotler, B. and Stotler, R. E.
2005. A revision of the genus Fossombronia Raddi in
East Asia and Oceania. Journal of Hattori BotanicalLaboratory 98: 1–45.