Pseudocyclosorus, Ching, Ching

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 73-74

PSEUDOCYCLOSORUS

Pseudocyclosorus Ching, Acta Phytotax. Sin. 8:322–324. 1963.— TYPE: Pseudocyclosorus tylodes (Kunze) Ching [= Aspidium tylodes Kunze ]— Cyclosorus subg. Pseudocyclosorus (Ching) Panigrahi — Thelypteris sect. Pseudocyclosorus (Ching) Fraser-Jenk. — Thelypteris subg. Pseudocyclosorus (Ching) Fraser-Jenk.

For synonymy, see Holttum (1974d),Holttum and Grimes (1980), Li et al.(2019).

Etymology.— Pseudocyclosorus Latin pseudo, false + Cyclosorus (Gr.) ; a distinct genus segregated from a broadly circumscribed Cyclosorus .

Plants terrestrial, often along streamsides, or shady forest understories, medium sized, 40–150 cm tall; rhizomes short-creeping or forming erect caudices (e.g., P.tylodes ); scales light brown, glabrous; fronds monomorphic, arching to erect; stipes stramineous, castaneous, or dull brown; stipe scales often sparse or caducous, when present, brown, glabrous or with marginal hairs, ovate to lanceolate; blades chartaceous, drying green, brown, or olivaceous, gradually reduced towards apex, proximal pinnae abruptly reduced to a series of opposite auriculate pinnae, these often caudate and/or hastate (see fig. 2 in Li et al. 2019), or reduced to a series of peg-like aerophores ( P. tylodes ); proliferous buds absent; pinnae sessile, or short-petiolulate, bases truncate, margins deeply lobed, lobes nearly perpendicular (e.g., P. esquirolii ) to strongly oblique (<45 degrees from costae in P. falcilobus ); veins free, reaching sinus, translucent sinus membrane often with tuft of hairs; aerophores swollen and conspicuous, protruding from mucilage in developing fronds; indument abaxially of spreading hairs restricted to axes, of various lengths, minute (<0.1 mm) to medium-sized (0.5 mm), stipes often with long tangled hairs; small spherical, sessile or stipitate golden (but never sulfurcolored) glands sometimes present on axes; indument adaxially of hyaline acicular hairs, restricted to axes, and sometimes also abundant on laminae between veins ( P. canus ); pustules lacking; sori round, discrete, rarely confluent, medial, along costules, or inframarginal, sometimes restricted to distal portion of pinnae, always indusiate, indusium typically large, especially evident on young fronds, persistent, glabrous or with short hairs or glands; sporangia with capsules lacking glands or hairs, capitate hairs sometimes present on sporangial stalks; spores monolete with cristae or echinae ( Grimes 1980; Li et al. 2019); x = 36 or 35, six species counted, diploids, triploids, and tetraploids known. A base number of 35 has been published for three species, based on several counts from multiple authors, and if correct this represents a dysploid change from the ancestral base number 36, which is synapomorphic for the cyclosoroid clade. Loyal (1961) reported a triploid P. canus with irregular meiosis from Darjeeling, representing a possible infrageneric hybrid. Shieh and Tsai (1987) reported a putative hybrid between Glaphyropteridopsis erubescens and Pseudocylosorus esquirolii , a finding that warrants further investigation.

Diagnosis.—The combination of deeply dissected pinnae, swollen aerophores (most easily observed in fiddleheads and fresh material), large indusia, and proximal pinnae abruptly reduced to auricles (or aerophores in P.tylodes ) is diagnostic for Pseudocyclosorus . Trigonospora may be distinguished by its trilete spores and erect (vs. usually creeping) rhizomes. Christella rarely has deeply divided pinnae with free veins, and often bears orangish pear-shaped glands. Plesioneuron has similar deeply incised pinnae with free veins, and large persistent indusia, but does not overlap in geographic distribution, and often has more thickly chartaceous (and sometimes pustulate) laminae, pinna bases often short-petiolulate and rounded or cuneate (vs. sessile and truncate), and stipe scales usually thick and persistent (vs. thin and caducous). Sphaerostephanos and Strophocaulon both may have abruptly reduced auriculate pinnae, but often bear yellowish glands, and are largely non-overlapping with Pseudocylosorus geographically.

Biogeography and ecology.— Pseudocyclosorus , here circumscribed to include 14 species, is most diverse at middle elevations of the Pan-Himalayan region. Pseudocyclosorus tylode s occupies the most extensive range, occurring from Sri Lanka to the Philippines. Two species, P. esquirolii and P.falcilobus , reach as far north as Japan. Three species occur in Afro-Madagascar. Members of the genus are typically plants of streamsides and forest understories.

Taxonomic and phylogenetic studies.— Ching (1936, 1940) recognized the species now treated in Pseudocyclosorus as a natural group in early publications, but did not name the genus until later ( Ching 1963). Based on similarities in venation, Ching (1963) believed Pelazoneuron patens and P. kunthii might also be allied, but this is not supported by molecular evidence ( Smith & Cranfill 2002; Fawcett et al. in press). Species-level taxonomy of Pseudocyclosorus is highly variable among authors. Pseudocyclosorus sensu Ching ( Ching 1963; Lin et al. 2013) included two Chinese species of Trigonospora , a genus that was segregated by Holttum (1971) based on having trilete spores and lacking abruptly reduced proximal pinnae. Holttum and Grimes (1980) recognized twelve species in their generic treatment of Pseudocyclosorus . Later, the genus was greatly expanded, and 20 new species were described by Lin (in Shing & Lin 1999); 38 species are recognized in the Flora of China, including the two Chinese species of Trigonospora ( Lin et al. 2013) . However, in a recent revision of the species of the Pan-Himalayan region, Li et al. (2019) recognized only eight species, reducing 21 names to synonymy. It is apparent that Pseudocyclosorus would benefit from a densely sampled molecular study. For example, the species boundary between P. subochthodes and P.esquirolii is unclear ( Li et al. 2019), and phylogenetic studies that have included multiple accessions of P.esquirolii ( He & Zhang 2012; Fawcett et al. in press) have resolved that species as paraphyletic; these results suggest that further study, especially of widespread and variable taxa, is warranted.

Herein, we adopt a conservative, morphology-based classification largely following Li et al. (2019), pending further study and a greatly expanded phylogenetic dataset, preferably including taxa recognized by Lin et al. (2013). An even more conservative taxonomic concept of this group is favored for species of India by Fraser-Jenkins (1997, 2008b), who considered several species and varieties to be synonymous, and treated Pseudocyclosorus as a subgenus of Thelypteris s.l.

Pseudocyclosorus is sister to Trigonospora plus a clade of two species from Madagascar, Pneumatopteris humbertii and Pronephrium fidelei. This clade is in turn sister to Abacopteris , treated herein as a small genus of Southeast Asia and eastern Malesia. Two species here tentatively maintained in Christella s.s., C. chaseana and C. gueintziana, resolve in Pseudocyclosorus in some individual gene trees (Fawcett et al. in press), suggesting possible hybrid origin. They are not closely related to other species of Pelazoneuron , where Holttum (1974a) treated them, despite striking superficial similarity ( Moran & Smith 2001).

Constituent species.— Pseudocyclosorus camerounensis Holttum ; * P. canus (Baker) Holttum & J.W. Grimes ; * P.esquirolii (Christ) Ching ; * P.falcilobus (Hook.) Ching ; P. gamblei Holttum & J.W. Grimes ; P. griseus Holttum & J.W. Grimes ; P.johannae Holttum ; P. ochthodes (Kunze) Holttum ; * P.ornatipes Holttum & J.W. Grimes ; P. pseudofalcilobus W.M. Chu ; * P. pulcher (Bory ex Willd.) Holttum ; P. stramineus Ching ex Y.X. Lin ; * P. subochthodes (Ching) Ching ; * P. tylodes (Kunze) Ching

Taxa treated in Plesioneuron .— Pseudocyclosorus caudatus Holttum ; P. excisus Holttum. These were both described in Pseudocyclosorus ( Holttum & Roy 1965) and later transferred to Pneumatopteris ( Holttum 1973a) .

Names of uncertain status.— Pseudocyclosorus duclouxii was treated as dubious by Li et al. (2019); P. furcovenulosus Y.X. Lin, P. guangxianensis Ching ex Y.X. Lin , P.pectinatus Ching , and P.submarginalis Ching ex Y.X. Lin were treated in Flora of China, but are known from few collections that are unavailable for study, and were not included in the revision by Li et al. (2019). Pseudocyclosorus tibeticus Ching & Y.X. Lin was excluded from the Flora of China ( Lin et al. 2013), pending further study.

Incertae sedis.— Pseudocyclosorus petrophila (Copel.) Holttum , from New Guinea ( Holttum & Roy 1965), treated as Pneumatopteris petrophila (Copel.) Holttum in later works, shares the opposite, hastate-auricled reduced proximal pinnae of mainland Pseudocyclosorus and free veins shared among all species, but is a major geographic outlier. It may have closer affinities to Plesioneuron or Sphaerostephanos , but we do not believe it is close to Pneumatopteris , where Holttum (1973a) later treated it. Pronephrium articulatum (Houlston & T. Moore) Holttum was recovered as nested within Pseudocyclosorus in recent Bayesian phylogenetic analyses, with 99% posterior probability ( Patel et al. 2019a). However, it differs in having up to four pairs of anastomosing veins below the sinus, proximal sori sometimes elongate, and unusual venation not seen elsewhere in the family: abaxially, veins are prominent until reaching sori, and obscure beyond them. The large, persistent indusia agree well with Pseudocyclosorus but, pending further data confirming its placement in Pseudocyclosorus , we refrain from making a new combination. A species of the Seychelles and São Tomé (see Holttum 1974a), Sphaerostephanos elatus (Bojer) Holttum is well supported as sister to Pseudocyclosorus in the nDNA analyses of Fawcett et al. (in press), but is well supported as sister to three species we now recognize as Abacopteris in studies relying primarily on cpDNA (e.g., Patel et al. 2019a). Sphaerostephanos elatus differs from all species in Pseudocyclosorus in having several pairs of veins anastomosing below the sinus, but it is alike in having the characteristic proximal pinnae abruptly reduced to triangular auricles, and large, persistent indusia. In our phylogenetic analysis (Fawcett et al. in press) the Afro-Madagascan P.pulcher is sister to all other Pseudocyclosorus , with the core clade of the genus all from the Pan-Himalayan region.