Abacopteris, Fee, Gen. Fil., Fee, Gen. Fil.

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 22

ABACOPTERIS

Abacopteris Fée, Gen. Fil. 309, t. 18 C. 1852.

— TYPE: Abacopteris philippinarum Fée,Congr.Sci. France 10(sess.1):178.1843. [= Abacopteris aspera (C.Presl) Ching, Acta Phytotax.Sin. 8:332.1963,based on Goniopteris aspera C.Presl ] ( Figs. 5D, 5E ).

Etymology. —Gr. abakos, abacus + pteris, fern. The venation and sori resemble an abacus, or counting frame; a calculating tool.

Plants terrestrial, medium to large (> 1m); rhizomes long-creeping, rarely short-creeping; fronds monomorphic, pinnate, erect to ascending; stipes stramineous, dull brown, or reddish, with hairy or glabrous brown linear-lanceolate scales on stipe bases and rhizomes; blades membranaceous to chartaceous, drying green, each with conform or rarely subconform terminal pinna ( A. hirtisora ) and no proliferous buds, proximal pinnae not or only slightly reduced; pinnae entire to crenate or shallowly lobed <1/3 to costae ( A. hirtisora ), bases cuneate or truncate, sessile or short-petiolulate; veins prominent abaxially, many pairs anastomosing between secondary veins (costules), with excurrent included veinlet, or continuous excurrent vein that is usually straight (occasionally zig-zag), costae adaxially grooved; aerophores present as darkened swellings at pinna bases; indument abaxially of hairs on and between veins, sometimes grading into small clear stipitate glands; indument adaxially of hyaline, unicellular, acicular hairs on costae and veins; pustules absent or sometimes present on adaxial lamina; sori round, medial, rarely coalescent (e.g., A. gymnopteridifrons ), indusiate or exindusiate, indusia light brown and hairy when present (e.g., A. aspera ); sporangia usually setulose, rarely glabrous; spores light brown or black, in A. aspera with fimbriate crests ( Patel 2019a); x = 36, with diploids and tetraploids known.

Diagnosis.— Abacopteris is distinguished from Pronephrium s.s. and Sphaerostephanos by monomorphic fronds and lack of yellow spherical glands on indusia. It is distinguished from Grypothrix by lack of hamate hairs, and from Menisciopsis and Grypothrix by sori medial and discrete (rarely coalescent or inframedial), setulose sporangia, and fronds often membranaceous and rarely drying reddish. For complete synonymy, see Holttum (1972, 1974a, 1982) and Lin et al. (2013).

Biogeography and ecology.— Abacopteris comprises about 14 species. Most of the species diversity of Abacopteris is restricted to continental South Asia, at lower elevations up to about 1800 m. Several species were recently described by Lin et al. (1999) in Pronephrium , most of which are narrow endemics in China, and known only from the type collections at PE. Abacopteris gymnopteridifrons is distributed in southern China and the Philippines, and the variable and widespread A. aspera occurs throughout Malesia, northern Queensland, Australia, and into the Pacific ( Holttum 1982) as far east as Fiji. The earliest diverging species in the genus is A. hirtisora , which occurs in Laos, India, and Thailand ( Lin et al. 2013).

Taxonomic and phylogenetic studies. — Holttum (1971, 1982) treated Abacopteris as a synonym of Pronephrium , an earlier name. However, the type of Pronephrium , P. lineatum , shares many morphological features (e.g., dimorphic fronds, indusia with spherical yellow glands) with members of Holttum’s Pronephrium sect. Dimorphopteris , and we believe it is allied more closely to those taxa than to the type of Abacopteris . In our view, the best solution is to resurrect the genus Abacopteris , and recognize a newly circumscribed Pronephrium , corresponding closely to Holttum’s Pronephrium sect. Dimorphopteris (1982) . Our current circumscription of Abacopteris includes members of Holttum’s Pronephrium sect. Pronephrium (1972) and also some taxa he treated in sect. Menisciopsis ( Holttum 1982) . We also include here two species previously treated in Sphaerostephanos ( A. hirtisora , A. peltochlamys ). One of these, A. peltochlamys , was originally recognized in Abacopteris by Holttum (1954) but was later transferred to Sphaerostephanos ( Holttum 1982) . This species is unusual in having 2–4 pairs of proximal pinnae abruptly much reduced, and sporangia bearing stipitate glands. For further discussion on the treatment of Pronephrium sensu Holttum and our recircumscription, see our description of Pronephrium .

In the Thelypteridaceae phylogeny (Fawcett et al. in press) Abacopteris is a member of the pseudocyclosoroid clade, sister to a clade that includes all sampled members of Pseudocyclosorus and Trigonospora , in addition to African taxa recently treated in Sphaerostephanos , Christella , and Pneumatopteris by Holttum (1974a) but distantly related to the type species of those genera. Amblovenatum and Christella s.s. also fall within the pseudocyclosoroid clade, and are part of the larger christelloid clade, that also includes the sphaerostephanoids and Strophocaulon ( Fig. 1 ).

Figures

FIG.5.A.Menisciopsiscyatheoides,Takeuchi1719 (UC),pinna lobes,abaxial view.B.M.boydiae,Baldwin116 (US),habit.C.Menisciopsisrubrinervis,Fawcett716 (VT), pinna,abaxial view.Abacopteris aspera,James 1693 (VT).D. pinna.E.pinna,abaxial view.

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