Cyclosorus, sensu Copeland, 1947

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 40-42

CYCLOSORUS

Cyclosorus Link, Hort. Reg. Bot. Berol. 2:128. 1833.

— TYPE: Cyclosorus gongylodes (Schkuhr) Link [= Aspidium gongylodes Schkuhr ] = Cyclosorus interruptus (Willd.) H. Ito

For additional synonymy, see Holttum (1982).

Etymology.—Gr. kyklos, circle + sorus, sori; ferns with round sori.

Plants terrestrial, medium-sized (> 40 cm) to large (fronds to ca. 100 cm tall); rhizomes very long-creeping, branching, blackish when dried; rhizome scales sparse or nearly absent back from the rhizome apex; fronds distant (to 10 cm apart), monomorphic, pinnate-pinnatifid, erect or arching; stipes blackish at bases, stramineous distally, adaxially grooved; stipe scales sparse, ovate-lanceolate, brown, setulose on margins and glabrous on surfaces; blades chartaceous to subcoriaceous (often somewhat leathery), drying greenish or reddish, pinnate-pinnatifid, with proximal pinnae not reduced or lowermost pair only slightly so, lacking auricles at acroscopic base; blade apices usually short, pinnatifid to subconform and pinna-like but usually much shorter than longest lateral pinnae; rachises generally hairy to glabrous or glabrescent, hairs if present 0.1–1.0 mm long, not scaly, lacking proliferous buds in axils of pinnae; pinnae 10–30 pairs, linear-lanceolate, short-stalked (1–4 mm), usually alternate or becoming alternate distally, lacking auricles, bases rounded to truncate, adaxially with a groove that is not continuous with the rachis groove, shallowly lobed ca. 1 ⁄ 4 – 1 ⁄ 2 their width, or in C. striatus to ca. 5/6 their width; veins simple, 9–18(–30) pairs per segment, usually prominent on both sides, unbranched, basal pairs from adjacent segments united at an obtuse angle below the sinus, and forming an excurrent vein (usually 2–4 mm long) running to the sinus, next pair more oblique and meeting margin at or just above the sinus, free vein ends reaching segment margins; aerophores inconspicuous or absent at pinna bases, not swollen; indument abaxially of stipes, rachises, costae, veins, and often laminar tissue between veins lacking or of hyaline acicular, spreading hairs, these 0.1–0.4 mm, blades lacking capitate hairs, often (on C. interruptus ) with orangish to reddish, sessile, spherical glands on costules, veins, and sometimes on laminar tissue between veins, also with scattered ovate, flat, pale brown scales on costae and sometimes on costules and veins in C. striatus ; indument adaxially of generally short (ca. 0.2 mm) hyaline, unicellular setae on stipes, rachises, and costae, hairs lacking on veins and tissue between veins; pustules absent on laminar tissue on both sides; sori medial to supramedial, circular, often absent from proximal 1 or 2 pairs of veins, not coalescent at maturity, indusiate, indusia sparingly hairy or glabrescent on margins and sometimes on surfaces, caducous with age; sporangia without setae or glands on the capsules, but often each with orangish to reddish long-stalked (2–4 cells) gland on the sporangial stalk; spores dark brown, with perispore irregularly spinulose or with short perforate ridges, lacking thin wings; x = 36 (both spp. counted), diploids and tetraploids known (see Notes), intergeneric hybrids not known.

Diagnosis.— Holttum (1971, 1982) considered the essential characters of the genus to include the very long-creeping, nearly scale-less rhizomes, blades truncate at the base (without greatly reduced proximal pinnae), anastomosing veins (usually one pair), costae bearing persistent flat, ovate scales abaxially, the presence of long-stalked glands on the sporangial stalks and receptacle (illustrated by Holttum et al. 1970; Smith 1971), and often sessile orangish or reddish glands on the laminae. No other genus shares this combination of characters.

Biogeography and ecology.— Cyclosorus s.s., as defined here, includes only two or three species ( Holttum 1971, 1974a, 1982), plants of freshwater swamps and wetlands, in ponds, or along streams and rivers, tropics and subtropics, growing at generally low elevations, 0–1000(–1800) m. The type species of Cyclosorus is pantropical, extremely polymorphic, and not recently studied over its broad range. Smith (1971) tentatively recognized three varieties in the American tropics, from Florida, Antilles, southern Mexico to Bolivia, Uruguay, and Paraguay. This same species, perhaps comprising other varieties, occurs in Africa, southeastern Asia, Malesia, Melanesia, Australasia, and Polynesia (including Hawai’i). The second species, C. striatus , is restricted to tropical Africa and is clearly related, based on both morphology and nucleotide sequence data. A late Miocene fossil described by Robledo et al. (2015) from Argentina , is referable to C. interruptus , suggesting the species is at least 5 mya.

Taxonomic and phylogenetic studies.— Holttum (1971) provided a general characterization of the genus in its restricted sense and later (1974a, 1977b, 1982) offered treatments of Cyclosorus in Africa, the Pacific and Australasia, and Malesia.In his 1974a paper he also presented a tentative key to all species in Cyclosorus , separating the glabrous variants as C. tottus (Thunb.) Pic.Serm. , with a South African type (many glabrous plants also occur in the Neotropics), and C. interruptus s.s., variously hairy, with a southern Indian type. In the same paper he also acknowledged that species intermediates existed. Because the elements and intricate interrelationships within this complex have been inadequately studied over their entire range, we prefer, in this work, to subsume C. tottus within C. interruptus , the oldest name in the complex.

Prior to Holttum’s seminal works mentioned above, most authors included several other genera within Cyclosorus . This broad circumscription was adopted by Copeland (1947) and followed by many subsequent authors. Even after Holttum’s studies, Lin et al. (2013) and Li (2013), working primarily with Chinese species, included Christella within Cyclosorus , as well as the genera Sphaerostephanos , Pneumatopteris , and Amblovenatum . All of these segregates are recognized as genera herein. By extension, the genera Amblovenatum (formerly Amphineuron), Mesopteris , Pakau , Reholttumia , Strophocaulon , and other genera as well, are often included in an expanded concept of Cyclosorus . Without providing new evidence, an extreme view was adopted by Mazumdar and Mukhopadhyay (2013), who subsumed all cyclosoroid genera within Cyclosorus . As discussed by Smith (1990), if one adopts that taxonomy, the earliest available generic name is Meniscium ( Stegnogramma also preempts Cyclosorus ). An even more extreme taxonomic view was taken by Christenhusz and Chase (2014), who included all thelypteroid genera—about 1200 species—in the single genus Thelypteris . As a consequence of recent phylogenetic insight (especially He & Zhang 2012; Almeida et al. 2016; and Fawcett et al. in press), reconsideration of morphological characters, and a judgment that a more finely constructed taxonomy facilitates further evolutionary studies, we here choose to recognize Cyclosorus in its most restricted sense.

Cyclosorus belongs to the large cyclosoroid clade, which is defined by the synapomorphy of x = 36, and by most species having anastomosing veins. Cyclosorus forms a clade with the southeast Asian genus Mesophlebion plus the paleotropical Ampelopteris , and these three are in turn sister to the neotropical Meniscium ( Fig. 1 ). Holttum (1977b, 1982) considered the closest relationship of Cyclosorus to be with predominantly temperate Thelypteris s.s., which has only two species, and with monotypic Ampelopteris , but affinity with Thelypteris s.s. is now thought to be remote ( He & Zhang 2012; Almeida et al. 2016; Patel et al. 2019a; Fawcett et al. in press). Possibly, the similar habitat—marshes and swamps—influenced Holttum to think the two genera were related.

Notes.—Spores of both Cyclosorus species were described as having “cavate folds with echinate elements” and “short, perforate ridges” by Tryon and Lugardon (1991), and spores of their Panamanian accession of C. interruptus and Ugandan C. striatus resemble C. interruptus material from New Zealand ( Patel et al. 2019a), but differ from the spores observed in material from China, which have few broad crests and little secondary sculpturing (Dai et. al. 2002; Wang & Dai 2010). The spores of the related genus Ampelopteris ( Tryon & Lugardon 1991, fig. 153.4) are virtually indistinguishable from the Cyclosorus spp. spores imaged in the same plate, while spores of Mesophlebion also have broadly winged spores with little secondary sculpturing ( Tryon & Lugardon 1991, figs. 153.5, 153.6).

Chromosome counts are known from plants of C. interruptus growing in Ghana, Tanzania, Japan, India, Sri Lanka, and Japan.Manton and Sledge (1954) found meiotic irregularities, with both triploid and tetraploids from Sri Lanka, but most counts made from plants of the Paleotropics are diploid. Two counts from neotropical localities, Florida and Jamaica, are tetraploid. The taxonomic significance of these regional ploidy differences is unknown, but it seems quite possible, even likely, that C. interruptus , as construed herein, represents a species complex. The second species, C. striatus , has been counted as diploid.

Constituent species.—* Cyclosorus interruptus (Willd.) H. Ito ; * C. striatus (Schum.) Pic.Serm.

Excluded species.—Many species in the family have combinations in Cyclosorus (see Mazumdar & Mukhopadhyay 2013), but only two species are included in our concept, which follows Holttum (1971) and PPG I (2016). Excluded species belong to many different genera in our treatment, especially, Amblovenatum , Christella , Goniopteris , Meniscium , Mesopteris , Pelazoneuron , Pneumatopteris , Pronephrium and its segregate genera, Reholttumia , and Sphaerostephanos .

Figures

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