Phegopteris

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 64-65

PHEGOPTERIS

Phegopteris (C. Presl) Fée, Mém. Foug. 5:242–243. 1852.

— LECTOTYPE (designated by Ching, Acta Phytotax. Sin. 8(4):312. 1963): Phegopteris polypodioides Fée (based on Polypodium phegopteris L.) [= Phegopteris connectilis (Michx.) Watt ]

Lastrella (H. Ito in Nakai & Honda) Nakai

For additional synonymy, see Holttum (1969).

Etymology. —Gr. phegos, beech + pteris, fern, a fern of beech forests.

Plants terrestrial, small to medium-sized (20–60 cm); rhizomes long-creeping, branching, subterranean, or short, ascending, or erect, with pale to brown, ovate scales with marginal hairs; fronds monomorphic, erect to arching; stipes dull-stramineous, terete to shallowly grooved adaxially; stipe scales stramineous to brown, ovate to lanceolate with marginal setulae; blades chartaceous to membranaceous, deciduous, with no clear articulations, broadly ovate-deltate, broadest at or near base of lamina (e.g., P. hexagonoptera ) or lanceolate, tapering towards apex and base ( P. decursivepinnata ), pinnate-pinnatifid to nearly bipinnate (e.g., P.koreana ), with alate rachises (sometimes proximal pinna-pairs free), these often with small, vascularized extensions of laminar tissue connecting adjacent pinnae; pinnae deeply lobed, segments entire, or with crenate to lobed margins, pinna-bases adnate, with decurrent wings to next pinna-pair, sometimes bases of proximal one or two pinna-pairs narrowed and sessile (e.g., P. connectilis ); veins free, often forking, reaching margin of lamina, or terminating near margin; aerophores absent; indument abaxially and adaxially of hyaline acicular hairs and narrow, hyaline, lanceolate scales with setulose margins, borne on rachises, costae, veins, and laminar tissue, or restricted to axes; pustules absent; sori medial, discrete, exindusiate, rarely with small indusium; sporangia sometimes with acicular or capitate hairs; spores smooth with essentially no ornamentation (e.g., P. decursive-pinnata), a low reticulum, or tubercules ( Patel et al. 2019a; Kim et al. 2004), also with an adnate perine (a feature apparently unique within the family ( Tryon & Lugardon 1991)); x = 30, with diploids, triploids, and tetraploids known, based on counts of five of the six species. For Phegopteris decursive-pinnata, all three cytotypes have been reported, suggesting further study is needed. Phegopteris connectilis is predominantly triploid throughout its circumboreal distribution, though diploid cytotypes are known from Japan ( Matsumoto 1982). The North American allotetraploid, previously treated within P. connectilis , has been segregated as Phegopteris excelsior ( Patel et al. 2019b) . Apomixis is known to occur in P. excelsior , and both apomictic and sexual populations of P. connectilis and P. decursive-pinnata are reported. Although no hybrids are known, there is compelling evidence for hybrid speciation ( Driscoll et al. 2003; Patel et al. unpubl. data). See Chandra (1963, 1974) for illustrations of anatomy and microscopic features.

Diagnosis. —The primarily north-temperate and montane Phegopteris may be distinguished from its mostly tropical sister genus, Pseudophegopteris , and closely related tropical genus Macrothelypteris by the adnate pinna-bases, and winged rachises with vascularized projections between pinnae (vs. pinnae mostly free, with only the distal pinnae adnate). Additionally, the stipe-scales of Phegopteris bear setulae restricted to the margins, while stipe-scales of Pseudophegopteris and Macrothelypteris also bear setulae on the scale surfaces ( Lin et al. 2013; Holttum 1969).

Biogeography and ecology. —The six species of Phegopteris are primarily north-temperate, with a few subtropical montane occurrences as far south as Taiwan, occurring from near sea-level to 3600 m. They may be terrestrial or epipetric, in shady forest understories, or along streams, or in open, disturbed sites. The apomictic triploid, Phegopteris connectilis , has among the broadest geographic ranges of any vascular plant species, extending throughout the northern temperate and boreal forests of Europe, Asia, and North America. Two species, P. hexagonoptera , and P. excelsior , are endemic to eastern North America, and two are endemic to East Asia, P. koreana to Korea, and another, P. tibetica , known from the type, collected from montane conifer forests in Tibet and in neighboring Nepal (Fraser-Jenkins et al. 2015). Phegopteris decursive-pinnata is widespread in continental temperate and subtropical Asia, also extending to Taiwan and Japan.It has recently been reported as naturalized in the southeastern United States, where it likely escaped from cultivation (Florez-Parra & Keener 2016).

Taxonomic and phylogenetic studies. —When Fée (1852) elevated Phegopteris to generic status, his concept included over 50 species with morphologically similar sori and venation, and subsequently hundreds of combinations spanning a diversity of currently accepted fern families were published in that genus. More than a century later, Ching (1963) was the first to recognize the genus in its current, narrow circumscription, also recognizing the close affinity, but distinctness, of two segregate genera, Pseudophegopteris and Macrothelypteris . These three genera together constitute one of the two subfamilies, Phegopteridoideae . The remaining genera of Thelypteridaceae are within the Thelypteridoideae ( PPG I 2016).

All molecular phylogenetic studies to date ( Smith & Cranfill 2002; He & Zhang 2012; Schneider et al. 2013; Almeida et al. 2016; Patel et al. 2019a; Fawcett et al. in press) have corroborated the monophyly of Phegopteridoideae , and the monophyly of its three constituent genera. Phegopteris is sister to Pseudophegopteris , and that combined clade is sister to Macrothelypteris .

Notes.— Phegopteris decursive-pinnata has been the subject of several important studies on fern reproductive biology. Its study has contributed to our understanding of the functional differences in breeding systems in diploids vs. tetraploids ( Masuyama 1979) and the mechanisms underlying gametophytic self-incompatibility ( Masuyama 1986). It has also yielded insight into the pathways to autopolyploid speciation, which has been rarely studied in ferns ( Nakato et al. 2012; Kawakami et al. 2019). Because of the ease of propagation, the diversity of ploidy and breeding systems, and strong foundational work, Phegopteris remains an excellent candidate for future experimental study.

Constituent species.—* Phegopteris connectilis (Michx.) Watt ; * P. decursive-pinnata (H. C. Hall) Fée; * P. excelsior N.R. Patel & A.V. Gilman ; * P. hexagonoptera (Michx.) Fée ; P.koreana B.Y. Sun & C.H. Kim ; P. tibetica Ching.