Steiropteris

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 85-86

STEIROPTERIS

Steiropteris (C. Chr.) Pic.Serm., Webbia 28:449. 1973.

— Dryopteris subg. Steiropteris C. Chr., Biol. Arb. til. Eug. Warming 81:1911.—

Thelypteris subg. Steiropteris (C. Chr.) K. Iwats. — Lectotype (chosen by Christensen, Kongel. Danske Vidensk. Selsk. Skr., Naturvidensk.

Math.Afd., ser.7, 10:164.1913): Steiropteris deltoidea (Sw.) Pic.Serm. [= Dryopteris deltoidea (Sw.)Kuntze ]. ( Figs. 9A, 9B ).

Glaphyropteris C. Presl ex Fée, Crypt. Vasc. Brésil 2:40. 1873.— Dryopteris subg. Glaphyropteris (C. Presl. ex Fée) C. Chr. — Thelypteris subg. Glaphyropteris (C. Presl. ex Fée) , Alston, nom. inval.— Thelypteris sect. Glaphyropteris (C. Presl ex Fée) C.V. Morton — Steiropteris subg. Glaphyropteris (Fée) A.R.Sm. , nom.inval.— Lectotype (chosen by Christensen,Ind.Filic.XXI, 1906): Steiropteris decussata (L.) A. R.Sm.,based on Polypodium decussatum L.[= Dryopteris decussata (L.) Urb.]

For additional synonymy, see Smith (1980).

Etymology. —Gr. steira, keel + pteris, fern. The keel, or false vein located abaxially, below the sinus ( Fig. 9B ), is a distinctive feature of many (but not all) species in this genus.

Plants terrestrial, or occasionally rheophytic, small (<15 cm) to very large (> 2 m); rhizomes short-creeping to suberect; fronds monomorphic to rarely subdimorphic (e.g., S. valdepilosa ) or weakly subdimorphic ( S. leprieurii ), pinnate to usually pinnate-pinnatifid, erect or arching; stipes stramineous to dull brown; stipe scales brown, lanceolate, setose; blades chartaceous, laminae drying dark green; rachises usually lacking buds in axils of distal pinnae (except in S. seemannii ); pinnae shallowly to often deeply lobed, rarely subentire to crenate, proximal pinnae not or little reduced, or abruptly reduced to many pairs of auriculate pinnae ( S. deltoidea , Fig. 9A ), distal pinnae gradually to sometimes abruptly reduced and with subconform, or hastate apices (e.g., S. insignis , S. setulosa ); veins running to sinuses or 1–several pairs anastomosing just below each sinus, forming a cartilaginous keel running to sinus ( Fig. 9B ), sometimes veins truly united below sinuses with an excurrent vein to the sinus, in a few species lowermost pair from adjacent segments meeting margins just above sinus and lacking a raised keel, vein endings reaching segment margins; aerophores often present at pinna bases, and sometimes at segment bases, these scale-like, tuberculate, or horny protuberances, persistent on old fronds; indument abaxially lacking or of sparse to dense, short to long, hyaline acicular hairs, these unicellular or septate, generally restricted to costae, costules, and veins, amorphous appressed scales often present on costae; indument adaxially lacking except along costae and rachises, rarely of hairs on lamina between veins; glands generally absent abaxially, but reddish, sessile, and resinous, in some spp. sometimes treated in subg. Glaphyropteris; pustules usually absent on laminar tissue abaxially and adaxially, except in a few species ( S. pennellii , S.seemannii ); sori round, subcostular, inframedial, or medial, not coalescent at maturity, indusiate or exindusiate; indusia, if present, glabrous, glandular, or short-hairy, sometimes vaulted, glandular, persistent or evanescent, hidden and/or shriveled at maturity in a few species; sporangia usually without setulae or glands, rarely setulose ( S. setulosa ) and rarely with orangish, stalked, globose glands from the receptacles ( S. valdepilosa ); spores monolete, brownish, narrowly winged with crenate or fimbriate crests, or rugose with closely packed, anastomosing ridges ( Wood 1973; Smith 1980; Patel et al. 2019a); x = 36, two of 25 spp. counted, diploids and tetraploids known. No interspecific or intergeneric hybrids are known.

Diagnosis. —Certain species of Steiropteris (e.g., S. decussata ) resemble some Amauropelta species (e.g., A. thomsonii ); both genera may have mucilaginous croziers, peg-like aerophores, enormous fronds (> 2m), and free veins, and both occur in disturbed or open tropical montane habitats. These two groups are easily distinguished by the presence of fasciculate hairs in this subgroup of Amauropelta (vs. simple hairs in Steiropteris ), tiny abortive pinnae at the blade bases in Amauropelta (vs. blades without abortive pinnae in Steiropteris ), fewer pairs of widely placed (> 1 mm apart) veins in Amauropelta (vs.> 20 pairs of veins ca.0.5 mm apart in the Steiropteris decussata and allies), and base chromosome number of x = 29 in Amauropelta thomsonii and allies (vs. x = 36 in Steiropteris ).

Biogeography and ecology. —Among the 26 species recognized in Steiropteris , one is restricted to the Lesser Antilles ( S. clypeolutata ), four to the Greater Antilles ( S. deltoidea ( Figs. 9A, 9B ), S. hottensis , S. lonchodes , S. wrightii —the last three narrowly endemic to Hispaniola or Cuba), and four are endemic to southern and Atlantic forests of Brazil ( S. hatschbachii , S.mexiae , S. polypodioides , S. villosa ). Three species are widespread and variable in the Neotropics ( S. decussata , S. gardneriana , S. leprieurii ), especially in South America, and the remaining 14 species occur in southern Central America ( Costa Rica, Panama) through the Andes to Bolivia and also the Coastal Cordillera of Venezuela ( Smith 1980; Smith & Kessler 2017). Several species are quite rare, local, and known only from the types or from very few localities. Most species occur in low and middle elevation tropical and montane rain forests, below 2000 m and usually below 1000 m; they mostly occur in relatively undisturbed primary rain forests, but S. decussata may occur at forest margins in partially exposed situations. Two Antillean endemics have greatly reduced blades and occur on stream banks, and thus can be considered rheophytes.

Taxonomic and phylogenetic studies. —The species of Steiropteris were treated by Christensen (1913) in two subgenera of Dryopteris : subg. Steiropteris included the keeled species; and subg. Glaphyropteris included those with free veins. Based on a suite of shared morphological features (see below), Christensen (1913), in his treatment of Glaphyropteris, included species now more appropriately placed in Amauropelta (e.g., Amauropelta thomsonii and allies— Thelypteris sect. Phacelothrix of Smith 1974). However, he included them tentatively, recognizing their numerous similarities to his Dryopteris subg. Lastrea (= Amauropelta ). The species circumscription of Steiropteris proposed in Smith’s (1980) monograph relied on morphological and cytological data and has not needed adjustment in consideration of molecular evidence.

The genus Steiropteris is monophyletic, but its two subgenera do not form two monophyletic clades, based on molecular evidence. Both plastid ( Almeida et al. 2016) and nuclear (Fawcett et al. in press) data indicate that Steiropteris is early diverging within the cyclosoroids, but the backbone relationship between Steiropteris , the stegnogrammoids, and a clade including all other cyclosoroid genera remains unresolved ( Fig. 1 ).

Some keeled species of Steiropteris greatly resemble Old World members of the genus Mesophlebion ( Fig. 9 ) in the convergent, connivent veins, conspicuous and cartilaginous sinus membrane, and presence of swollen aerophores at the bases of pinnae; but these similarities appear to be due to convergence or represent the plesiomorphic condition in the cyclosoroids ( Fig. 1 ). Holttum (1982:378) commented on the “often pale violet-purple” color of young sporangia in Mesophlebion , a condition also seen in some species of subg. Steiropteris . There are morphological similarities, too, between Steiropteris and Goniopteris , especially in blade dissection and venation, but the latter genus is almost always distinguished by bearing furcate or stellate hairs (such hairs lacking in Steiropteris ); Goniopteris is well removed from Steiropteris in the phylogenetic analysis of Fawcett et al. (in review) ( Fig. 1 ). Several character states that are rare in Steiropteris are common in other cyclosoroid genera, e.g., rachis buds and pustular laminae.

Combinations for all known accepted species of Steiropteris have been made by Pichi Sermolli (1973), Salino et al. (2015), Smith and Kessler (2017), and by Salino and Smith (2018), except:

Figures

FIG. 9.Steiropteris deltoidea,Fawcett 464 (VT) A. habit.B. pinna lobes,adaxial view.C.Mesophlebion sp., Karger 1796 (VT),pinna lobes,abaxial view.

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