Metathelypteris

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 58-59

METATHELYPTERIS

Metathelypteris (H. Ito) Ching, Acta Phytotax. Sin. 8:304. 1963.— Thelypteris sect. Metathelypteris H. Ito , in Nakai & Honda

— Type: Metathelypteris gracilescens (Blume) Ching [= Aspidium gracilescens Blume ]

For additional synonymy see Lin et al.(2013).

Etymology. —Gr. meta, near, close to + Thelypteris . This genus is a distinct from, but close to, Thelypteris .

Plants terrestrial, small to medium-sized, usually 35–100 cm tall; rhizomes short-creeping to suberect or erect, often with tufted fronds; fronds monomorphic, arching to erect, pinnate-pinnatifid to barely bipinnate and with adnate pinnules (e.g., M. flaccida ); stipes green when living, stramineous or reddish-flushed with age, scaly only at bases, scales tan to brown, mostly 2–7 mm long, lanceolate, bearing short acicular hairs on margins and on surfaces; blades membranaceous to chartaceous, ovate-deltate to lanceolate, proximal pinnae not or only slightly reduced, apices confluent, gradually tapering; pinnae opposite or subopposite, often becoming alternate distally, sessile, usually deeply lobed to ca. 1 mm from costae; rachises hairy to sometimes glabrescent, lacking vegetative buds, with acicular hairs; veins free, simple ( M. gracilescens ) or often forked in ultimate segments, with thickened ends (seen adaxially) ending short of segment margins; costae adaxially prominent, not grooved; aerophores absent; indument abaxially on axes (rachises, costae, costules, and veins) and sometimes on laminar tissue of acicular, unicellular hairs and/or stipitate glands, lacking spherical or hemispherical glands and scales; indument adaxially generally lacking, except along rachis and costae, but if present hairlike (uniseriate); sori round, often near tips of veins, and on acroscopic branch of forked veins, indusiate, indusia round-reniform, thin, glabrous or with short setulae and/or stipitate glands on margins and sometimes on surfaces; sporangia short-stalked, glabrous or sometimes bearing hairs of several cells on stalks, lacking glands and hairs on sporangial capsules; spores dark brown, with irregular, variously anastomosing ridges; x = 31 ( M.uraiensis ), 34 ( M. gracilescens ), 35 ( M. dayi , M. flaccida , M. singalanensis ), and 36 ( M. laxa ) (6 spp. counted), both diploids and tetraploids known. A base number of x = 35 is the predominant report (three species), and other base numbers need verification, as there are several cases of conflicting reports within a species.

Diagnosis.— Metathelypteris differs from Amauropelta (which see for additional discussion) and Coryphopteris in the costae and rachis lacking adaxial grooves, veins not reaching the segment margins (viewed adaxially), laminae truncate with proximal pinnae not greatly reduced (a characteristic shared with most members of Coryphopteris ), and x = usually 35 (vs. x = 27, 29, 31, 32, 33, rarely 35). There are also similarities with some species in the phegopteroid clade ( Phegopteris , Macrothelypteris , Pseudophegopteris , which mostly lack or have relatively small indusia (as sometimes in Macrothelypteris ), generally have larger, more broadly deltate, and more divided blades, and have different chromosome base numbers (x = 30, or 31, vs. x = usually 34 or 35 in Metathelypteris . Metathelypteris shares with the phegopteroid genera the characteristics of often-forked veins that end before reaching the margin, the costae and main rachis adaxially lacking grooves, and generally the lack of reduced proximal pinnae.

Biogeography and ecology.— Metathelypteris comprises ca. 17 species, distributed from Bioko and São Tomé (both having endemic species), tropical Africa and South Africa ( Holttum 1982; Pichi Sermolli 1983) and Madagascar, to India, Sri Lanka, China, continental southeast Asia, southern Japan, and Malesia, east to the Solomon Islands. It is most diverse in continental Asia, while seemingly absent from most of Melanesia, Australia, New Zealand, and all of Polynesia. Species occur in middle elevation forests, from ca. 1000–2000 m, often on steep earthy slopes or among rocks, occasionally in somewhat open places ( M. flaccida ), especially along trails.

Taxonomic and phylogenetic studies. — Ching (1963) first recognized Metathelypteris as a genus, and Holttum (1971) adopted a similar circumscription. Holttum (1976a, 1982) later expressed belief that Metathelypteris was most closely related to Macrothelypteris and especially Pseudophegopteris , agreeing with these genera in having free, often forking veins that end before reaching the segment margins and costae lacking adaxial grooves. Despite these morphological similarities, molecular evidence suggests that Metathelypteris is sister to Amauropelta s.l. (including Parathelypteris s.s.), with Coryphopteris sister to Metathelypteris + Amauropelta ( He & Zhang 2012; Almeida et al. 2016; Fawcett et al. in press), and not ancestral to the phegopteroid clade, as Holttum (1976a) thought.

Notes.—Fraser-Jenkins et al. (2017) recently synonymized M. deltoideofrons Ching ex W.M. Chu & S.G. Lu under M.decipiens , M.krameri Sarn.Singh & Panigrahi under M.flaccida , and M. tibetica Ching & S.K. Wu under M.uraiensis . We have seen scant material of these heterotypic synonyms, but tentatively accept their conclusions, pending a muchneeded modern monograph of Metathelypteris .