Thelypteris

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 88-89

THELYPTERIS

Thelypteris Schmidel, Icon. Pl. , ed. Keller, 3, 45, t. 11 B, 13. 1763, nom. cons.

— TYPE: Thelypteris palustris Schott [based on Acrostichum thelypteris L., Sp. Pl.2:1071.1753]

Lastrea Bory nom. illeg.superfl.

Hemestheum Newman nom. illeg.superfl.

Etymology.— Gr. thelys, female + pteris, fern. An old Greek name for a fern more delicate than the male fern, Dryopteris filix-mas ( Stewart et al. 1983) .

Plants terrestrial, small to medium-sized, in wet ground (often marshes or swamps), dying back in winter (in temperate areas); rhizomes short- to often long-creeping, usually blackish, with relatively few roots between nodes, mostly 1.5– 3 mm diam.; fronds moderately sized (typically 30–100 cm), monomorphic or weakly dimorphic, with fertile fronds narrower and having longer stipes and more constricted pinnae and segments, arching to erect, deeply pinnate-pinnatifid or often pinnatisect with pinnae incised to within 1 mm of costae; stipes dull stramineous, blackened at bases; stipe scales tan, ovate, glabrous or nearly so; blades chartaceous, drying green, proximal pinnae not reduced, or with 1–several pinna-pairs somewhat reduced, but never abruptly reduced to a series of hastate auricles or glanduliform pinnae; blade apex gradually reduced; proliferous buds absent; pinnae nearly symmetrical with segments spreading or only slightly oblique; margins entire, pinna bases sessile to short-petiolulate, truncate, acroscopic segment often slightly elongate but not auriculate; veins free, simple or often forked, ending at margins of lobes just above sinuses ( Fig. 6D ); aerophores absent; indument abaxially of hyaline acicular hairs restricted to axes (rachis, costae, and sometime costules), also with thin, flat, ovate tan scales along costae, tissue between veins glabrous or nearly so; indument adaxially of hyaline acicular or tortuous hairs restricted mostly to costae, veins and laminar tissue glabrous; pustules absent; sori typically round and discrete, or often confluent at maturity, medial or inframedial, indusia relatively large and persistent, glabrous or with a few short-stipitate glands; sporangia glabrous or often bearing short, stipitate glands <0.1 mm; spores tan, bilateral, monolete, perispore variable, echinate in T. confluens , and granulate, papillate, irregularly tuberculate, or reticulate and perforate in T. palustris ( Tryon 1971, Tryon et al. 1980, Tryon & Lugardon 1991); x = 35, two species, only one counted, always diploid. Reports of n = 36 for T. palustris , by Mitui (1968) and Hirabayashi (1969), from populations in Japan, are likely erroneous (see Tryon & Tryon 1973, for comments and a review of cytological information).

Diagnosis.— Thelypteris can be readily distinguished from the superficially similar, and sometimes co-occurring amauropeltoid genera by a combination of characteristics. It has consistently long-creeping, relatively narrow rhizomes (1.5– 3 mm diam.); grows in persistently wet habitats in temperate areas; has largely scaleless rhizomes behind the apex; has persistent ovate scales on the costae abaxially ( Fig. 6D ); lacks greatly reduced proximal pinnae; has frequently forked, free veins on the ultimate segments ( Fig. 6D ); and is often slightly dimorphic, with fertile fronds taller, and with confluent sori resulting in an almost acrostichoid appearance. Thelypteris may be distinguished from both Amauropelta and Coryphopteris in temperate latitudes by the presence of scales on the abaxial costae, the lack of glands on abaxial laminae, some veins forking (vs. simple), and fidelity to wetland habitats.

Biogeography and ecology. —Throughout their range, the two species of Thelypteris s.s. occur in perennially wet, often open areas, especially marshes, peat bogs, forested swamps, and edges of lakes. Thelypteris palustris is widespread in temperate wetlands of the northern hemisphere, while Thelypteris confluens , is south-temperate in sub-Saharan Africa, southern India, northern Thailand, parts of Malesia, Australia, New Zealand, and southern South America. Outlying populations of both T. palustris and T. confluens occur sporadically in suitable habitats in the tropics and subtropics.

Taxonomic and phylogenetic studies. —Historically, the genus Thelypteris has had many different circumscriptions. Beginning with Ching (1936), and continuing with Morton (1963), the genus was accepted in a broad sense, comprising all or most of the ca. 1000 species in the family Thelypteridaceae . Before that time, members of the family had usually been subsumed in an unwieldy genus Dryopteris (e.g., Christensen 1913, 1920). Ching (1963) recognized 18 genera within Thelypteridaceae for mainland Asia, and restricted Thelypteris to just three species. Shortly thereafter, Holttum (1969, 1971, 1982, 1983) adopted many of Ching’s generic concepts and also segregated several new genera; a series of revisions and monographs culminated in recognition of 23 genera in Asia ( Holttum 1982), and Thelypteris s.s. with either two or three species. An attempt at some middle ground was offered by Smith (1990) and later by Christenhusz et al. (2011). Smith recognized five genera in the family, with the largest genera being expanded concepts of both Thelypteris (ca. 280 spp,. in five subgenera, including subg. Thelypteris with two spp.) and Cyclosorus (ca. 525 spp. in 20 subgenera).

Holttum (1983) proposed a slightly different narrow classification of the genus, recognizing three species. In this, he distinguished European T. palustris s.s., with glabrous indusia, from the North American taxon, having hairy indusia; he called the latter T. thelypteroides (Michx.) Holub. However , as shown earlier by Tryon et al. (1980), that name is based on a mistypification by Morton (1967) and applies to Amauropelta noveboracensis (see discussion under Amauropelta ; see also comments regarding typification by Tryon et al. 1980). Regardless of the typification issue, we regard the European and North American variants as conspecific.

The two species of Thelypteris recognized by us and many others (e.g., Tryon et al. 1980) are only subtly different. Thelypteris palustris is largely restricted to north-temperate North America, Europe, and Asia. Fernald (1929) was the first to distinguish infraspecific variants within Thelypteris palustris s.l. —one in Eurasia ( var. palustris ), the other in North America and eastern Asia ( var. pubescens (G. Lawson) Fernald ). A third variant, var. haleana Fernald , in the southeastern U.S.A., Cuba, and Bermuda, was also distinguished by Fernald and others; however, it is only dubiously distinct, according to Tryon et al. (1980), and we concur. The southern hemisphere taxon, T.confluens , has been recognized as a distinct species by most recent authors, including Morton (1967), Tryon et al. (1980), and Holttum (1983), but was treated as T. palustris var. squamigera (Schlecht.) Weatherby by Tryon (1971) and Fernald (1929).

Thelypteris tremula Christ , type from Michoacán, Mexico, is probably only an outlier of the widespread Northern Hemisphere T. palustris var. pubescens ( Mickel & Smith 2004), to which it is sister in the phylogenetic analysis of Fawcett et al. (in press). Most Mexican collections are more than 100 years old, and it seems likely that T.tremula is largely extirpated, with draining of its habitat; however, one recent collection is Rzedowski 39234 ( IEB, XAL). Thelypteris fairbankii (Bedd.) Y.X. Lin et al. was recognized by Lin et al. (2013) but seems likely to be a heterotypic synonym of T.confluens .

All phylogenetic studies with broad sampling ( He & Zhang 2012; Almeida et al. 2016; Fawcett et al. in press) show Thelypteris s.s., as treated here, sister to the rest of Thelypteridoideae ( Fig. 1 ). This subfamily includes 900+ species, and is sister to the smaller subfam. Phegopteridoideae ( Macrothelypteris , Pseudophegopteris , Phegopteris ). Thelypteris s.s. represents an ancient lineage, diverged from its closest extant relatives by perhaps 86 Ma ( Testo & Sundue 2016).

Constituent species.—* Thelypteris confluens (Thunb.) C.V. Morton ; * T. palustris (Salisb.) Schott ( Fig. 6D ).

Figures

FIG. 6. A. Plesioneuron hopeanum, Fawcett 613 (VT),pinna lobes,adaxial view.Amauropelta (subg.Nibaa) noveboracensis, Fawcett 567 (MICH,VT),B. pinna-lobes, adaxial view.C.habit.D. Thelypterispalustris,Fawcett 569 (VT),pinna lobes abaxial view.

FIG. 1. A synoptical treeillustrating relationships among genera of Thelypteridaceae based on Fawcett et al.(in press).