Metzgeria epiphylla A. Evans

Materials

Type status: Other material. Occurrence: catalogNumber: PE 02162938; recordNumber: 4664; recordedBy: W. Han; occurrenceID: 7F65BDC7-D662-5D03-B467-A8B609B1FC94; Taxon: class: Jungermanniopsida; order: Metzgeriales; family: Metzgeriaceae; Location: continent: Asia; country: China; countryCode: China / CN; stateProvince: Hubei; county: Shennongjia Forestry District; municipality: Muyu Town; locality: Shennong Valley; verbatimLocality: Next to the boardwalk; verbatimElevation: 2820 m; verbatimLatitude: 31°26'19.47″N; verbatimLongitude: 110°16'52.0″E; Identification: identifiedBy: Y. Jia and Q. He; Event: year: 2023; month: 9; day: 18; habitat: On the trunks of Abies fargesii Franch. in the forest

Type status: Other material. Occurrence: catalogNumber: PE 02154417; recordNumber: 948; recordedBy: Z. Q. Yi and J. Wu; occurrenceID: 636DFB31-73E3-5D9A-9ADC-1AC5AEF439C2; Taxon: class: Jungermanniopsida; order: Metzgeriales; family: Metzgeriaceae; Location: continent: Asia; country: China; countryCode: China / CN; stateProvince: Hubei; county: Shennongjia Forestry District; municipality: Muyu Town; locality: Banbi Rock; verbatimLocality: In the gully; verbatimElevation: 2590 m; verbatimLatitude: 31°27'26.35″N; verbatimLongitude: 110°13'41.44″E; Identification: identifiedBy: Y. Jia and Q. He; Event: year: 2023; month: 5; day: 14; habitat: On the branches

Description

The plant is yellow-green to pale green, lacking blue spots when dry, forming loosely interwoven mats attached to the substrate (Fig. 1 a). The thallus is prostrate, irregularly forked, flat or slightly convex, with adventitious branches arising from the midrib on the ventral side. Mature thalli are 0.6-1.2 mm wide, occasionally up to 1.5 mm and 1-1.2 cm long (Fig. 1 f). Branches are spaced 1-2.5 mm apart and exhibit two apex forms: one rounded and blunt (Fig. 1 b-d), the other tapering into a short, sharp point (Fig. 1 e). The midrib in cross-section has two layers of elliptical epidermal cells on both dorsal and ventral surfaces, measuring 25 × 15 μm, with three layers of 10 medullary cells, which are round to elliptical, thin- or thick-walled and 15-20 μm in diameter (Fig. 1 h). The thallus is 16-22 cells wide from the midrib to the margin, with central cells approximately 40 μm in diameter and marginal cells slightly smaller at 25 μm (Fig. 1 f).

Sparse spiny hairs occur along the leaf margins, usually solitary, measuring 0.1-0.2 mm long and 8-10 μm wide (Fig. 1 g). Numerous gemmae are found along the edges or near the margins of narrow, specialised branches. These gemmae are variable in shape, ranging from round, elliptical, to elongated rod-like forms, flat or slightly convex, with short spiny hairs along the edges or ventral surface (Fig. 1 i-n).

The species is dioecious. Male branches are nearly spherical, smooth, measuring 0.3-0.4 mm long and 0.25-0.35 mm wide. The female perichaetial leaves are broadly obovate, 0.3-0.35 mm in length and width, with spiny hairs on the edges and ventral surface. The capsule is brown, oval-shaped, typically ranging from 0.5-0.6 mm in length and 0.35-0.4 mm in width and the valves, when spread out, measure 0.6-0.75 × 0.2-0.25 mm. The calyptra measures approximately 1 mm in length and 0.45 mm in width, with abundant hairs above the middle and sparse, scattered hairs below. The spores are pale yellowish-brown and finely punctulate, with a diameter of 16-18 μm. Elaters are 0.3-0.4 mm long, 6 μm wide at the middle and bear a single broad spiral band extending the entire length. Gemmae are sometimes abundant, arising from more or less narrowed and specialised branches with limited growth, positioned either marginally or submarginally and dorsally and are orbicular to oval in shape, either flat or slightly convex, with a few short marginal hairs that are slightly displaced to the concave surface (Evans 1923).

Distribution

China (present study), Chile (Evans 1923), Tristan da Cunha, Papua New Guinea and New Zealand (Kuwahara 1978 b, Piippo 1991).

Ecology

This discovery represents a significant extension of the known distribution of M. epiphylla, confirming its presence in China, specifically in the evergreen broadleaf forests of Shennongjia National Park, where it inhabits tree trunks, branches and leaves at altitudes ranging from 1400 to 2900 m (Fig. 2 a-c). Evans (1923) documented that plants of M. epiphylla preferred living leaves as a habitat, although they occasionally grew on bark. However, Piippo (1991) further described that the species occurred in montane rainforests of the Huon Peninsula and was specifically found on tree trunks. This habitat description closely aligned with the location where we discovered M. epiphylla in the present study.

Taxon discussion

During the bryophyte survey in Shennongjia National Park, two specimens of M. epiphylla were collected. Both specimens were identified, based on their morphological characteristics and matched the diagnostic features of M. epiphylla, as described in the original species description from South America (Evans 1923). The thallus was pale green, loosely interwoven and epiphytic, with irregularly forked branching patterns. Thalli measured 0.6-1.2 mm in width, occasionally reaching up to 1.5 mm, which differs from Evans (1923) ' s original description, where mature thalli rarely exceeded 1 mm. Kuwahara (1978 b) observed various forms of the thallus in M. epiphylla, although he did not provide specific measurements. This suggests that the thallus of the species exhibits a certain degree of variability, likely due to environmental factors or other sources of plasticity.

Further microscopic examination revealed detailed structural features consistent with M. epiphylla. The midrib consisted of two layers of epidermal cells, with three layers of medullary cells. The midrib cells were elliptical and measured 25 × 15 μm, while the medullary cells were 15-20 μm in diameter. Leaf edges had sparse spiny hairs measuring 0.1-0.2 mm in length. Spores were light brown, with a finely warty surface and measured 16-18 μm in diameter. The elaters exhibited single spiral thickenings, measuring 0.3-0.4 mm in length and approximately 6 μm in width. These characteristics confirm the identity of M. epiphylla and distinguish it from closely-related species within the genus.