Pneumatopteris, Nakai, Nakai

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 68-70

publication ID	https://doi.org/ 10.17348/jbrit.v15.i2.1206
persistent identifier	https://treatment.plazi.org/id/03B787F6-FFA7-9B1B-623A-7DEAFDB6F9AC
treatment provided by	Donat
scientific name	Pneumatopteris
status

Treatment

PNEUMATOPTERIS View in CoL

Pneumatopteris Nakai View in CoL in Bot. Mag. (Tokyo) 47:179. 1933.

— TYPE: Pneumatopteris callosa (Blume) Nakai View in CoL [= Aspidium callosum Blume View in CoL ]

For additional synonymy, see Holttum (1973a, 1977b, 1982).

Etymology.— Gr. pneuma, air, breath + pteris, fern. The peg-like pneumatophores (aerophores) extending from the stipe, and the bases of the pinnae (and sometimes the bases of the costules) are diagnostic for this genus ( Fig. 2C View FIG ).

Plants terrestrial, large (to 2 m tall), often along streams; rhizomes thick (> 1cm), creeping, or forming erect caudices with fronds densely clustered; fronds monomorphic, pinnate-pinnatifid, arching; stipes stramineous, scales brown, broadly ovate to ovate-lanceolate, glabrous, or often with hairs along margins; blades generally coarse in texture (chartaceous to subcoriaceous), often bicolorous, drying darker green adaxially; lamina apex gradually reduced or with subconform terminal pinna, proximal pinnae abruptly reduced to minute vestigial pinnae, with a fringe of laminar tissue surrounding aerophores (1–4 mm); pinnae sessile, with truncate bases, shallowly lobed (generally <1 ⁄ 2 to costae), with pronounced cartilaginous sinus membranes that are grooved adaxially ( Fig.7A View FIG ) and project out of the plane of the blade abaxially, segment tips generally acute; veins prominent above and below, often paler than lamina, with at least one pair anastomosing below each sinus, forming an excurrent vein to sinus, with more distal veins running to both sides of an elongate sinus membrane, veins closely spaced, (7–)11–12(–15) pairs per segment; aerophores prominent, peg-like ( Fig. 2C View FIG ), projecting through mucilage during early frond development, along stipes, and at pinna bases, frequently also with peg-like or swollen aerophores at the bases of costae; indument abaxially essentially lacking, or of generally short hyaline acicular hairs on veins and/or between veins; indument adaxially essentially lacking, or of abundant short hairs on and between veins (these sometimes glandular, or capitate, e.g., P.glabra ), and long, antrorsely arching or curling reddish or brownish hairs in the adaxial grooves of the rachis and costae (hairs absent in P.callosa ); pustules lacking, or present on lamina adaxially and abaxially (e.g., P. stokesii ); sori round, medial to inframarginal, exindusiate, sometimes with receptacular hairs ( P. glandulifera ), or with a small indusia that may be glabrous or setose (e.g., P. mesocarpa ), often shriveling or caducous upon maturation of sporangia; sporangia glabrous, setulose (e.g., P. parksii ) or glandular (e.g., P. glabra ), glands always colorless, setae acicular or capitate, unicellular or multicellular; spores yellow to light brown; likely x = 36, as is the case with all its close relatives, but no counts published. No hybrids have been formally documented, but certain specimens with malformed spores (e.g., Fawcett 638, Viti Levu, Fiji, UC, VT; Game s.n., UC 1544285, Rarotonga, Cook Islands) represent possible hybrids.

Diagnosis.— Pneumatopteris s.s. is distinguished from most other christelloids by having prominent aerophores along the stipe, at the bases of pinnae ( Fig. 2C View FIG ), and at the bases of costae; pinnae abruptly reduced to vestiges subtending aerophores (not more than a few mm in length); fronds producing mucilage during early development; and veins closely spaced (ca. 12 per segment). The pinna segments of Pneumatopteris s.s. typically have about 11 veins per cm (vs. typically about 7 veins per cm in Reholttumia ); laminae often strongly bicolorous, drying dark above and paler below; and prominent elongate sinus membranes concave adaxially and convex abaxially. Sphaerostephanos differs by having laminae sometimes gradually or subabruptly reduced, and having yellow spherical glands (glands in Pneumatopteris colorless, and usually capitate when present), and lacking mucilage on developing fronds. Reholttumia also differs in having laminae sometimes gradually or subabruptly reduced, pinnae often lobed more deeply (> halfway to costae), and segment apices usually truncate or obtuse rather than broadly acute in Pneumatopteris s.s. Strophocaulon differs in having long-creeping rhizomes (vs. erect or short-creeping with stipe bases closely clustered). Hoiokula differs in having a zig-zag excurrent vein, densely setulose sporangia (rare in Pneumatopteris s.s.), and hairs between veins on adaxial laminae. Pakau differs in having scales present on the abaxial costae, opposite or subopposite pinnae (vs. alternate), and lack of aerophores. Christella s.s. differs in generally having hairier laminae, on veins, and between veins.

Biogeography and ecology.—This relatively small clade, comprising just 11 species as defined here, is well represented in the Pacific, in Melanesia and Polynesia, with species occurring in the Solomon Islands, New Hebrides, Fiji, Samoa, Rarotonga, the Society Islands, and Rapa (but not in Hawaii). Several other species are Malesian, including the type, P. callosa , from Java. Species of Pneumatopteris occur primarily at low to middle elevations (0–2400 m) and are frequent along rocky rivers and streams ( Holttum 1977b).

Taxonomic and phylogenetic studies.— Pneumatopteris , as recognized by Holttum (1973a, 1974a, 1977b, 1982; in Hovenkamp & De Joncheere 1988), with only two additional species described since then (by Palmer 2005; Takeuchi 2007), included about 90 species extending from Africa to New Zealand. In molecular phylogenetic analyses, Pneumatopteris sensu Holttum is by far the most heterogeneous and polyphyletic taxon in the Thelypteridaceae , with representatives in ten major clades (Fawcett et al. in press). Even so, Holttum was well aware of the diversity within his concept of the genus, recognizing most members of Pneumatopteris s.s. as close relatives of one another, but also describing the unique morphology of four aberrant taxa we now place in four different genera, three of which are newly described. Other species we exclude from Pneumatopteris are newly combined in several existing genera: Abacopteris , Menisorus , Plesioneuron , and Sphaerostephanos , or placed in one of three new genera, which see for details: Pakau , Hoiokula , and Reholttumia .

The African species of Thelypteridaceae are under-collected and remain poorly represented in molecular analyses. However, recent work (Fawcett et al. in press) has illuminated many of the problems with the current taxonomy and highlights the need for further study. The four African species treated in Pneumatopteris by Holttum (1974a) included in the molecular analysis each resolved in a distinct clade, corresponding to different genera: Pneumatopteris afra in Abacopteris , Pneumatopteris unita as sister to Menisorus pauciflorus , Pneumatopteris remotipinna in Reholttumia , and Pneumatopteris humbertii as sister to Christella distans , both of which resolve in a clade with Trigonospora and Pseudocyclosorus .

The closest relative of Pneumatopteris s.s. is the monophyletic genus Sphaerostephanos , redefined slightly herein. A majority of the remaining species treated as Pneumatopteris by Holttum (1977b, 1982) are in a clade sister to these two clades (herein named Reholttumia ; Fig. 1 View FIG ). To preserve a monophyletic Pneumatopteris , Reholttumia must be segregated. Alternatively, Sphaerostephanos (the oldest name for the three groups) must be significantly expanded; this genus already includes nearly 200 species and is recognizable (albeit morphologically diverse). We prefer to recognize a smaller, well-defined Pneumatopteris s.s., and segregate the sister clade to Sphaerostephanos as Reholttumia .

Constituent species.— Pneumatopteris callosa (Blume) Nakai ; P. dicranogramma (Alderw.) Holttum ; P. dilatata Holttum ; P. florencei (A.R. Sm. & Lorence) A.R. Sm. & Lorence ; P. glabra (Copel.) Holttum ; P. glandulifera (Brack.) Holttum ( Fig. 2C View FIG ); P. mesocarpa (Copel.) Holttum ; P. obstructa (Copel.) Holttum ; P. parksii (F. Ballard) Holttum ( Fig. 7A View FIG ); P. sibelana Holttum ; P. stokesii (E.D. Br. ex E.D. Br. & F. Br.) Holttum

Pneumatopteris View in CoL as treated by Holttum (1974a, 1977b, 1982) includes about 90 species, but as we circumscribe it, only 11 species remain, one of which is newly combined. We transfer most of the others to other genera. Several species are excluded from Pneumatopteris View in CoL s.s. but remain unplaced, pending further study.

Species transferred to Reholttumia .— This newly described genus encompasses the greatest number of species treated as Pneumatopteris by Holttum (1971, 1982), and most of those he considered ‘typical’ of the genus. It is predominantly Malesian, but with representatives extending into Hawaii, Australia, Sri Lanka, and at least one species, with its affinities confirmed by molecular data, occurring in Africa: Pneumatopteris basicurtata Holttum ; P. boridensis Holttum ; P. bryanii (C. Chr.) Holttum ; P. christelloides Holttum ; P. costata (Brack.) Holttum ; P. ecallosa (Holttum) Holttum ; P. glaberrima (A. Rich.) Holttum ; P. hudsoniana (Brack.) Holttum ; P. inclusa (Copel.) Holttum ; P. jermyi Holttum ; P. kerintjiensis Holttum ; P. laevis (Mett.) Holttum ; P. laticuneata Holttum ; P. longipes (Blume) Holttum ; P. macroptera (Copel.) Holttum ; P. magnifica (Copel.) Holttum ; P. michaelis Holttum ; P. micropaleata Holttum ; P. nitidula (C. Presl) Holttum ; P. novae-caledoniae Holttum ; P. oxyoura (Copel.) Holttum ; P. papuana Holttum ; P. pergamacea Holttum ; P. psilophylla Holttum ; P. remotipinna (Bonap.) Holttum ; P. rodigasiana (T. Moore) Holttum ; P. sogerensis (Gepp) Holttum ; P. truncata (Poir.) Holttum ; P.vaupelii (C. Chr.) Holttum

Species recognized in Abacopteris .— A species, heretofore recognized in Pronephrium , was treated more recently in Pneumatopteris : P.nudata (Roxb.) Punetha & Kholia, J. View in CoL Bombay Nat. Hist. Soc. 86:476. 1990.

Species transferred to Hoiokula .— Two Hawaiian endemics, most closely related to Leptogramma , Stegnogramma , and Cyclogramma in the phylogeny of Fawcett et al. (in press), are transferred to this new genus: Pneumatopteris pendens D.D. Palmer ; Pneumatopteris sandwicensis (Brack.) Holttum.

Species transferred to Menisorus .— Previously recognized as monotypic, this genus now includes two species. Both share its proliferous buds, unusual among Thelypteridaceae : Pneumatopteris blastophora (Alston) Holttum ; Pneumatopteris unita (Kunze) Holttum.

Pneumatopteris subpennigera (C. Chr.) Holttum , from Madagascar, is similar but lacks proliferous buds and has elongate sori; we consider it incertae sedis.

Species transferred to Pakau .— A single taxon, native to New Zealand and northern Australia, is transferred to this monotypic genus: Pneumatopteris pennigera (G. Forst.) Holttum.

Species transferred to Sphaerostephanos . —Three species have been transferred to Sphaerostephanos , which was recently demonstrated to be a large, mostly monophyletic, but morphologically heterogeneous genus (Fawcett et al. in press): Pneumatopteris incisa Holttum ; P. microloncha (Christ) Holttum ; P.superba (Brause) Holttum.

Incertae sedis.—Certain species stand out as especially problematic due to limited sampling, unique morphological features (or lack of diagnostic features), and distributions in poorly collected regions of high diversity, or some combination of these factors, and we are unable to place these with confidence.

The karst regions of Papua New Guinea host an extraordinary diversity of Thelypteridaceae , and these are known from few herbarium collections and very limited molecular data. Some of these can be transferred with confidence to the genera Plesioneuron or Sphaerostephanos (see above); however, we were unable to study diagnostic microscopic features of type material, or sample tissue for molecular analyses of others. The following species of Papua New Guinea all share the following characteristics: small stature; epipetric habitat, predominantly on calcareous rocks; proximal pinnae gradually reduced, and shallowly lobed pinnae, often with free, or forking veins, or with few anastomosing pairs: Pneumatopteris cheesmaniae Holttum ; P. egenolfioides Holttum ; P. latisquamata Holttum ; P. nephrolepioides (C. Chr.) Holttum ; P.patentipinna Holttum ; P.petrophila (Copel.) Holttum (treated in Pseudocyclosorus by Holttum and Roy 1965); and P. versteeghii Holttum. The last taxon exhibits the asymmetrical pinna-bases typical of Plesioneuron , though its pinnae are not deeply incised. Outside of Papua New Guinea, several other diminutive rock ferns of diverse morphology are known and are also of uncertain placement: Pneumatopteris lithophila Holttum ; P. aberrans Holttum ; P. sumbawensis (C. Chr.) Holttum ; and P. brooksii (Copel.) Holttum. Some of these calciphilic rock ferns demonstrate an interesting parallel to the diversity of the New World genus Goniopteris on Caribbean karst ( Fawcett 2020).

An aberrant species with up to eight pairs of gradually reduced pinnae, Pneumatopteris auctipinna , resolves with support as sister to the four sphaerostephanoid genera, however, morphologically it is most similar to Reholttumia . Additional data are needed to confirm its placement.

The aforementioned Pneumatopteris humbertii , from Madagascar, as well as Christella distans and perhaps Pronephrium fidelei (Fawcett et al. in press), from the same area, are more closely related to Pseudocyclosorus and Trigonospora than either is to Pneumatopteris or any of its segregate genera; however, they are morphologically distinct from all species currently recognized in Pseudocyclosorus . We refrain from placing these taxa until a more complete understanding of the interrelationships of the African Thelypteridaceae can be achieved.

The African species Pneumatopteris afra (Christ) Holttum resolves variously with Christella s.s. or Abacopteris (Fawcett et al. in press), and our interpretation of its morphology is inconclusive; we refrain from making a combination, pending further study. The morphologically similar Thelypteris glandafra Viane was believed to be closely related to Pneumatopteris afra and P. blastophora ( Viane 1985) , but we treat the latter taxon in Menisorus . Further study is needed to place T.glandafra and an additional African taxon, Pneumatopteris oppositifolia , with confidence.

Finally, because of inadequate descriptions, incomplete type material, and/or aberrant morphology not corresponding closely to any current generic concept, we additionally treat the following taxa as incertae sedis: Pneumatopteris eburnea Holttum ; P. japenensis Holttum ; P. lawakii Holttum ; P. microauriculata Holttum ; P. prismatica (Desv.) Holttum ; P. subappendiculata (Copel.) Holttum ; P. tobaica Holttum ; P. transversaria (Brack.) Holttum ; P. usambarensis Holttum ; and P. venulosa (Kuntze) Holttum.

Excluded species.—We exclude Pneumatopteris lucida (Baker) Holttum , which is likely to have been described from a mislabeled specimen of P. laevis (Mett.) Holttum from the Philippines, not from Madagascar, as it was labeled in the cultivated collection at Kew ( Holttum 1973a).