Pronephrium (Holttum, 1982)

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 70-72

PRONEPHRIUM

Pronephrium C. Presl, Abh. KÖnigl. BÖhm. Ges. Wiss., ser. 5, 6:618. 1851, Oct.; Epimel. Bot. 258. 185, Oct.

— LECTOTYPE (designated by Holttum, Blumea 19:36.1971): Pronephrium lineatum (Blume) C.Presl [= Aspidium lineatum Blume ]

Dimorphopteris Tagawa & K. Iwats. in Iwatsuki, Acta Phytotax. Geobot. 19:8. 1961. — Pronephrium sect. Dimorphopteris (Tagawa & K. Iwats.) Holttum, Blumea 19:36.1971.— Type: Dimorphopteris moniliformis Tagawa & K. Iwats. in Iwatsuki,Acta Phytotax.Geobot.19(1):8, f.14.1961. [= Pronephrium moniliforme (Tagawa & K.Iwats.) Holttum ]

Nannothelypteris Holttum, Blumea 19:38. 1971.— Type: Nannothelypteris aoristisora (Harr.) Holttum, Blumea 19:38. 1971 [= Pronephrium aoristisorum (Harr.) S.E. Fawc.& A.R.Sm. ,based on Polypodium aoristisorum Harr. ]

For complete synonymy, see Holttum (1977b, 1982).

Etymology.—Gr. pro, in front of + nephros, kidney, referring to the reniform indusia covering the sori ( Stewart 1983); indusia in this genus may be round, or even absent.

Plants terrestrial, rheophytic or epipetric, typically small to medium-sized, mostly (8–)15–50(–70) cm tall; rhizomes short-creeping, ascending, or erect; fronds typically strongly dimorphic with fertile fronds often much taller (to 3×) than non-fertile fronds ( Fig. 7C ), erect or arching, and once-pinnate to pinnate-pinnatifid (rarely simple in juvenile plants); stipes stramineous to dull brown, with ovate-deltate to linear-lanceolate brown scales, typically with hairs on scales, rarely without; blades chartaceous to subcoriaceous, rarely membranaceous, with apex gradually reduced (e.g., P.affine C. Presl ), pinna-like (e.g., P.lineatum ), or much larger than lateral pinnae (e.g., P.granulosum (C. Presl) Holttum ), proximal pinnae not, or only slightly, reduced, lacking proliferous buds; pinnae margins entire, crenate, or shallowly lobed (some irregular long lobes projecting outward in P. xiphioides (C. Chr.) Holttum , rarely deeply lobed ( P. philippinum ), frequently with acroscopic basal auricles, sometimes also with basiscopic auricles, sessile or short-petiolulate, with truncate or broadly cuneate bases, in some species the pinnae strongly asymmetric ( Nannothelypteris group); veins prominent adaxially and abaxially, several pairs regularly anastomosing to form a straight, or somewhat zig-zag excurrent vein, less commonly with included veinlets ( P. menisciicarpon (Blume) Holttum ), in species with smaller pinnae (e.g., P. aoristisorum ) veins forked rather than anastomosing; vein endings reaching margins; aerophores rare, when present, as darkened swelling of aerating tissue; indument abaxially of hyaline acicular hairs on costae, veins, and sometimes on laminar tissue between veins, yellow or golden spherical glands frequently present; indument adaxially of hyaline acicular hairs, these restricted to costae and veins; pustules usually present and often dense on abaxial and adaxial laminae; sori medial, round, with or without indusia, when present, indusia glabrous or with acicular hairs and/ or golden spherical glands, generally paired on either side of excurrent vein, appearing acrostichoid on the most reduced fertile fronds; sporangia glabrous or with setae or yellow to golden spherical glands; spores light to dark brown, with fimbriate, anastomosing crests (e.g., P.peltatum ) ( Patel et al. 2019a); x = 36, with three species counted, representing two diploids ( P. hosei , P. camarinense ) and a tetraploid ( P.affine ). No hybridization has been formally demonstrated within the genus, but Holttum (1982) suggested that Pronephrium xiphioides may represent a hybrid (or a hybrid swarm) between P.granulosum and P.rhombeum .

Diagnosis.— Pronephrium s.s., as redefined here, is distinguished from the three other segregates of Pronephrium s.l. ( Menisciopsis , Abacopteris , and Grypothrix ) by its small stature (typically <50 cm tall), strongly dimorphic fronds, small pinnae (usually <4 cm wide), laminar apex sometimes gradually reduced, and yellow or golden spherical glands on abaxial lamina, indusia and/or sporangia. It also tends to grow at lower elevations than these taxa. Pronephrium lacks the hamate hairs on the blades and/or sporangia and has short-creeping to suberect rhizomes; hamate hairs occur on all known species of Grypothrix , and many species of that genus have long-creeping rhizomes. The yellow spherical glands found in some species of Pronephrium are shared with many species of Sphaerostephanos ,but are lacking in Pneumatopteris and Reholttumia , to which Pronephrium s.s. is more closely related than it is to other species segregated from Pronephrium s.l. Pronephrium s.s. is generally distinguished from Sphaerostephanos by proximal pinnae not, or only slightly, reduced (vs. abruptly or gradually reduced), and appressed hairs lacking on the adaxial laminae between veins (present in Sphaerostephanos glandulosum ). For complete synonymy, see Holttum (1982).

Biogeography and ecology.— Pronephrium includes approximately 37 species, is almost entirely Malesian in distribution, and is especially diverse in the Philippines. Some taxa extend into adjacent continental Asia (e.g., P.affine occurs in peninsular Thailand). One species, Pronephrium palauense , endemic to the island of Palau, extends the range of the genus into Micronesia. Most species occur at low elevations, many below 500 m, though some species reach 1800 m, along streams, or on calcareous rocks. Of the 45 species treated by Holttum (1982) in sect. Dimorphopteris, eight were known only from the type collection, and several others are known from only a few collections, suggesting that many may be rare, and therefore vulnerable to extinction; however, due in part to the subtle or microscopic characters needed to distinguish genera of Thelypteridaceae , this diverse family may be often overlooked by non-specialist collectors.

Taxonomic and phylogenetic studies.—Our observations suggest that P. lineatum , the type of Pronephrium , is distantly related to the other members of Holttum’s (1971, 1972, 1982) small but heterogeneous Pronephrium sect. Pronephrium , which includes species we now recognize in Abacopteris , Menisciopsis , and Sphaerostephanos (based on molecular phylogenetic data; Fawcett et al. in press). Thus, Pronephrium s.s., as defined herein, corresponds in large part to Holttum’s concept of Pronephrium sect. Dimorphopteris . A collection at Leiden (L:0052355, image!), presumably studied by Blume, was designated as lectotype of P. lineatum by Holttum (1971). Contrary to Holttum’s interpretation, we see this specimen as dimorphic, evidenced by the much longer stipe of the fertile frond. Holttum noted the spherical yellow glands and setulae on the sporangia, and glands on the indusia of the type, which, together with dimorphic fronds, are diagnostic for our concept of Pronephrium s.s. Holttum (1971) initially recognized Haplodictyum as a good genus, but later ( Holttum 1982) placed it in synonymy under Pronephrium ; we regard the type of Haplodictyum, and several similar species, to be part of Sphaerostephanos .

Based on the phylogeny in Fawcett et al. (in press), Pronephrium is a member of the sphaerostephanoid clade that also includes Sphaerostephanos , Pneumatopteris s.s., and Reholttumia (which includes a majority of species formerly treated in Pneumatopteris ). These four genera are together sister to the pseudocyclosoroid clade which includes Abacopteris (treated by Holttum as a heterotypic synonym of Pronephrium sect. Pronephrium ). The larger christelloid clade includes both the sphaerostephanoids and the pseudocyclosoroids. Pronephrium s.s. (our sense, defined herein) is more distantly related to Menisciopsis and Grypothrix , the other two segregates of Pronephrium sensu Holttum (1982) , which resolve in the chingioid clade. Nannothelypteris aoristisora , the type of Nannothelypteris , is nested within Pronephrium s.s., and is here treated as a synonym. Holttum (1982) was aware of the similarity of Nannothelypteris to Pronephrium sect. Dimorphopteris and believed they were closely related. Nannothelypteris , as treated by Holttum (1973b, 1982), is restricted to the Philippines and its species are distinct from most Dimorphopteris in having lanceolate blades with many (> 30) pinna-pairs. Two additional species of Nannothelypteris were described by Kato et al. (1997), extending the known range to the Moluccas, but one of these, N. seramensis M. Kato , does not display morphology typical of Nannothelypteris because of its large size and deeply incised and gradually reduced proximal pinnae. Its affinity is uncertain, but its macromorphology, geographic location, and glandular sporangia suggest it may belong in Sphaerostephanos .

Figures

FIG.7.A.Pneumatopteris parksii,Fawcett 645 (UC),pinna lobes,adaxial view.B.Reholttumia magnifica,Fawcett 676 (VT),pinna lobes,abaxial view.C.Pelazoneuron patens,Fawcett 744 (VT), abaxial pinna-lobes.D. P.serra,Fawcett 1034 (VT), adaxial pinna lobes.E. Pakau pennigera, Given 11842 (VT),pinna lobes,abaxial view. F.Pakau pennigera, Stuart s.n.(VT),pinna.