Oreopteris (Holub, 1969)

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 59-61

OREOPTERIS

Oreopteris Holub, Folia Geobot. Phytotax. 4:46. 1969.

— TYPE: Oreopteris limbosperma (All.) Holub [= Polypodium limbospermum All.]

Thelypteris subg. Lastrea (Hook.) Alston, J. Wash.Acad.Sci. 48:232.1958.

Etymology. —Gr. oreos, mountain + pteris, fern. A fern of the mountains.

Plants terrestrial, mostly (15–) 25–100 cm tall; rhizomes brown, suberect or erect, 5–10 mm diam. (excluding old stipe bases); fronds seasonal, dying back in winter, crowded and tufted, pinnate-pinnatifid, monomorphic, arching; stipes stramineous to tan above the base; stipe scales persistent, light brown to stramineous, thin, ovate to lanceolate, these lacking acicular hairs but marginally papillose; blades chartaceous, drying yellowish green, elliptic or oblanceolate, middle pinnae the longest, with 5–10 pairs of proximal pinnae gradually reduced, basal pair(s) sometimes auriculiform or glanduliform and ca. 2–10 mm long, blade apex gradually tapered, with distal pinnae not decurrent, proliferous buds absent; rachises stramineous to pale castaneous ( O. elwesii ), usually with persistent ovate to lanceolate, glabrous scales abaxially, sometimes with hyaline acicular, unicellular hairs 0.2–0.4 mm long; pinnae sessile or nearly so, grooved adaxially, lobed about halfway to costae ( O. elwesii ) to deeply pinnatifid to ca. 1 mm or less from costa, sometimes with basal acroscopic crenulate-margined auricles, on basal segments on both sides somewhat elongate; veins (3–)5–12 pairs per segment, simple or 1-forked, usually prominent abaxially and adaxially, lowermost pair from adjacent segments running to margin just above sinus between adjacent lobes, veins ending at pinna margins or nearly so; aerophores absent or distinctly swollen ( O. elwesii ); indument abaxially along costae of tan, linear, lanceolate or ovate scales, also sometimes with acicular hairs along costae, veins and tissue between veins usually lacking hairs (except near costae) or nearly so, sometimes (in O. limbosperma ) with numerous yellowish to occasionally orangish spherical glands ca. 0.1 mm diam., indument adaxially lacking or of hyaline acicular hairs on rachises and costae, sometimes also with short hairs or stipitate glands on and between veins, hairs on stipes and rachises 0.1–0.3 mm long, sparse to moderately dense, hairs if present single-celled; pustules absent on laminar tissue; sori inframarginal or medial, round, indusiate, indusia round-reniform, tan, persistent, glabrous or sometimes bearing minute capitate hairs, marginally toothed; sporangia glabrous or sometimes bearing glands; spores pale brown, echinate or with prominent irregular ridges that form a coarsely reticulate network ( Tryon & Lugardon 1991); x = 34 (unique within the family), all three species counted, only diploids known; intrageneric and intergeneric hybrids unknown.

Diagnosis.— Oreopteris is distinguished from Thelypteris s.s. by having suberect to erect rhizomes (vs. long-creeping); presence of persistent scales on the stipes, rachises, and sometimes on the costae abaxially; thin, glabrous stipe base scales; proximal pinnae gradually reduced (vs. proximal pinnae not reduced); sessile (vs. short-stalked), broader pinnae; and base chromosome number of x = 34 (vs. x = 35). The two genera also occur in different habitats. Holub (1969) discussed at length the characteristics distinguishing Oreopteris from Thelypteris s.s., but was unaware of a third species of Oreopteris , O.elwesii . From most Coryphopteris , which also usually has erect caudices, Oreopteris differs by the gradually reduced proximal pinnae, glabrous scales, and veins sometimes forked; Amauropelta subgenera Parathelypteris and Venus, both predominantly Asian, differ in the very narrow, almost filamentous long-creeping rhizomes. Oreopteris has reduced proximal pinnae similar to many Amauropelta spp. , but very different spore ornamentation (echinate or broadly ridged vs. reticulate and perforate in Amauropelta ; Wood 1973; Tryon & Lugardon 1991: fig.149.24–149.26). All necessary combinations have been made in Oreopteris by Holub (1969) and by Holttum (1981).

Biogeography and ecology.— Oreopteris comprises three species, O. limbosperma of Eurasia, O.quelpartensis (Christ) Holub (often spelled quepaertensis) of eastern Asia and North America, and O. elwesii (Baker) Holttum ( Holub 1969; Holttum 1971), confined to Sikkim (northeastern India) and Yunnan, China ( Lin & Iwatsuki 2013). In North America, O. quelpartensis is noticeably disjunct, with western populations in Alaska, British Columbia, and Washington, and eastern populations in Newfoundland ( Bouchard & Hay 1976; Smith 1993a). Species occur from near sea level to ca. 1800 m (– 3100 m for O. elwesii ). Species of Oreopteris are generally found in open, rocky woods and subalpine meadows, along streams, and in ditches in acidic soils.

Taxonomic and phylogenetic studies. — Ching (1963) was the first to recognize the two boreal species now recognized in Oreopteris as close relatives, treating them together within the genus Lastrea Bory. The name Lastrea historically has been variously applied to a great diversity of ferns with free veins, but Holub (1969) pointed out that the name was illegitimate because it was published with a list of type species that included the type of the earlier name Thelypteris . Accordingly, he proposed the name Oreopteris as a replacement for Lastrea sensu Ching. Holttum (1974e) later expanded the circumscription of the genus to include Oreopteris elwesii .

Most recent floras and fern classifications have followed Holub (1969) and Holttum (1981) in recognizing Oreopteris as distinct, e.g., Lin & Iwatsuki (2013), PPG I (2016). Older floras, e.g., Flora Europaea (1964) and Flora of North America North of Mexico (1993a), and classifications (e.g., Smith et al. 2006) often subsume Oreopteris in a broadly defined genus Thelypteris .

Oreopteris elwesii is rare in collections, poorly known, and divergent from the other two species on the basis of the following characteristics: short-creeping rhizomes (vs. erect or suberect); pale-castaneous stipe and rachis (vs. stramineous); distal portion of stipe and rachis lacking scales; swollen aerophores (vs. aerophores absent); narrower, less deeply incised pinnae (ca. ½ vs. ca. 4 ⁄5 their width or more); and its occurrence at higher elevation. The main characteristic keeping it in Oreopteris is its base chromosome number, x = 34. In the sum of its features, it resembles more some species of Amauropelta , which is an unlikely affinity on the basis of both geography and cytology (x = 29 in all Amauropelta subg. Amauropelta ). Further study is needed to confirm placement of this unique taxon in the genus. Oreopteris quelpartensis in Asia and North America appears to lack the large, yellow, spherical glands that characterize most specimens of O. limbosperma from Europe, which is sometimes described as lemon-scented ( Jermy 1964); most specimens of O. quelpartensis from North America are devoid, or nearly so, of acicular hairs of the sort found in most specimens of O. limbosperma . Holttum (1981) provided a key distinguishing the three known species.

In broadly based molecular analyses ( He & Zhang 2012; Almeida et al. 2016; Patel et al. 2019a; Fawcett et al. in press), Oreopteris is sister to the entire cyclosoroid clade, including all christelloids, goniopteroids, and stegnogrammoids ( Fig. 1 ). Holttum (1981) opined that Oreopteris was most closely related to Amauropelta , but in our analysis (Fawcett et al. in press), Amauropelta falls within the amauropeltoid clade, which is sister to all cyclosoroid genera plus Oreopteris . Both morphological and molecular evidence suggest that Oreopteris is nearly as evolutionarily isolated as Thelypteris s.s., and neither genus is closely related to any element in the diverse cyclosoroid or amauropeltoid clades.

Constituent species.— Oreopteris elwesii (Hook. & Baker) Holttum ; * O. limbosperma (All.) Holub ; * O. quelpartensis (Christ) Holub

Figures

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