Taxonomic studies of lycophytes and ferns from the Pan-Himalaya (II): Crepidomanes , Didymoglossum and Vandenboschia (Hymenophyllaceae)

Summary . The ferns family Hymenophyllaceae is one of the most interesting basal clades of ferns, which is widely distributed in tropical and subtropical regions, less common in temperate latitudes of both hemispheres. This work deals with the taxonomic study of the representatives of the subfamily Trichomanoideae , which according to the classification of PPG 1 (2016) in the region are represented only by three genera. Following the style of the treatment of the genus Hymenophyllum, this paper is the second report of our studies of the filmy ferns from the Pan-Himalaya which is a part of the ongoing “Flora of Pan-Himalaya” project. In the present account, the taxonomy of three genera of Hymenophyllaceae: Crepidomanes , Didymoglossum , and Vandenboschia from the Pan-Himalaya are carefully revised based on morphological characters and recent works in the region. Herbarium materials kept in the National Herbarium (PE) have been fully studied and compared with collections from the Himalayas kept in European herbaria (K, BM, E). The generic and infrageneric classifications follow those of Ebihara et al. (2006) which recognized only nine genera. In the Himalayas, only four genera represented, i. e., Hymenophyllum (10 species), Crepidomanes (5 species), Didymoglossum (1 species), and Vandenboschia (2 species). The synopsis includes a key for species identification, standard taxonomic citations for the genus, sections, species. For each taxon as well as of each synonym are verified and indicated, necessary literature citation, morphology descriprion and citation of the reprehensive specimens from the Pan-Himalaya are recorded, overall distribution is mentioned and distribution in the Flora of Pan-Himalaya area is mapped. Although this is only a precursor of the ongoing “Flora of Pan-Himalaya” project, it is useful for identification of new collections from the area, and provides basic information for the conservation and ecological studies of the filmy ferns from the Himalayas, a very sensitive area to global changes. Crepidomanes parvifolium and Didymoglossum sublimbatum in this region are critical endangered concerning their small populations and limited distribution.

The filmy fern family Hymenophyllaceae is one of the largest families among the modern representatives of pteridophytes, comprising ca. 600 species (Iwatsuki, 1990) or 434 species (PPG I, 2016). The peculiarities in morphological characters make them distinct from other ferns. The plant body is transparent and thin sheet-like structure. Terminal sori occur at the end of veins. The number of spores in each sporangium ranges from 64 to 512. Often, the spores begin to germinate in the sporangium, and they have the ability to germinate rapidly. Filmy species occur in very humid conditions in the tropical, subtropical and temperate regions of both Old and New Worlds, with highest diversity in mountainous tropical rain forests.
In the present study, a comprehensive review of the relevant literatures and a thorough examination of herbarium specimens from the Pan-Himalaya deposited at the Chinese National Herbarium (PE) and other European herbaria (BM, E, K) are conducted. The Pan-Himalaya comprises the northeastern Afghanistan, northern Pakistan, northern India, Nepal, Bhutan, northern Myanmar, and southwest China (S Tibet, SE Qinghai, SE Gansu, W Sichuan, and NW Yunnan). Modern systematics of this group is often disputed. Traditionally, only two genera were recognized in the family Hymenophyllaceae: Hymenopyllum and Trichomanes. This scheme was expanded by Morton (1968), who hierarchically placed many subgenera, sections and subsections under these two genera. Conversely, Copeland (1947) split this family into 34 genera. Recently, a new classification of this family was proposed by Ebihara et al. (2006), based on the past as well as recent investigation involving molecular phylogenetic analyses. The classification of Ebihara et al. (2006) divided the family into nine genera, of which four genera, i. e., Crepidomanes, Didymoglossum, Vandenboschia, and Hymenophyllum are represented in the Pan-Himalaya.
One species was found in Pan-Himalaya, more than 20 species are distributed throughout the tropics, mainly in the New World. Plants 1-2.8 cm tall. Rhizome long creeping, ca. 0.2 mm in diam., densely hairy; hairs brown, unicellular, oblong-linear, twisted, less than 0.4 mm long, root like shoot present. Stipes 5-9 mm apart, 1-3 mm long, densely hairy like the rhizome, narrowly winged except the base. Lamina simple, oblong to linear-oblong, 1-2.5 cm × 3.5-7 mm, base subtruncate to cuneate, gradually narrowing downwards, margin repand to sinuated lobed, lobe a quarter ways to costae, apex round or obtuse. Main vein bearing only sori; sometimes lateral vein present; lateral veins 3-4 paris, simple or forked, marginal false veinlet absent; false vein present, obliquely parallel to the lateral veins, long, ending within the margin, several lines up to 15 between adjacent veins. Sori 1-5 on apical part of frond, usually terminal on lobes; involucres tubular, 1.5-2 × 0.7-1 mm, completely immersed in frond, lips flaring and dilated, mouth up to 2 mm in diam., receptacle exerted. See Fig. 1 & 9A.
Note: Formerly, this species was placed in the genus Microgonium (Copeland, 1938;1947). But in the new classification system of Ebihara et al. (2006), it was placed into the genus Didymoglossum because of the lack of submarginal false veinlets.
Habitat: On muddy rocks or rarely on basal tree-trunks in dense forests, at 850 m. Plants epiphytic or rock, rarely terrestrial. Rhizomes long-creeping, frequently branching, filiform, densely covered with dark hairs, root absent, root-like shoot present. Lamina simple to quadripinnatifid, elliptic to subdeltate some dwarf species digitately divided. Venation anadromous, false veinlets mostly present but some species absent, submarginally (continuous or interrupted) and/or parallel (but not connected) to true veins, cell wall thin and straight. Sori paratactic, tubular, campanulate or obconic, often broadly winged, lips usually bilabiate, sometimes entire or dilated, receptacle exserted.
Habitat: On moss-covered rocks in forests at lower mid altitudes.
Habitat: On moist rocks or tree-trunks in shade area in forests at mid altitude 2000-3600 m. Species Plant epiphytic or lithophytic. Rhizomes longcreeping, frequently branching, filiform, covered with dark brown hairs or glabrescent, roots absent, root-like shoots present. Lamina simple to quadripinnatifid, flabellate to narrowly ovate, stipe and rachis filamentous, much branched, dark, wiry, often proliferations often observed. Venation anadromous, false veinlets absent, internal cell walls thin and straight. Sori paratactic or pantotactic, campanulate, immersed in the apices of the segment, lips dilate, receptacles long-exserted.
Habitat: Tree trunks or on rocks in forests and valley or wet rocks near streams, on moos-covered at low mid altitude.
Note: This species is one of the complex species of the Hymenophyllaceae, so many authors gave name based on the phonetic features.  Vandenboschia Copel. 1938, Philipp. J. Sci. 67 (1)  pitted). Sori paratactic, tubular to campanulate, lips sometimes dilate, receptacles long-exserted.

VANDENBOSCHIA
One species was found in Pan-Himalaya and more than 15 species throughout the tropics, extending to northern temperate regions.