Stegnogramma

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 83-85

STEGNOGRAMMA

Stegnogramma Blume, Enum. Pl. Jav. 172. 1828

.— TYPE: Stegnogramma aspidioides Blume — Thelypteris sect. Stegnogramma (Blume) Fraser-Jenk. — Thelypteris subg. Stegnogramma (Blume) C.F.Reed

Dictyocline T.Moore

For additional synonymy, see Kuo et al.(2019).

Etymology.— Gr. stegnos, cover, + gramme, line, in reference to the sori, which are borne along the veins ( Stewart et al. 1983).

Plants terrestrial, frequently of steeply sloping tropical and subtropical forest understories and shaded streamsides, small to large (15–50 cm); rhizomes short-creeping to ascending or erect, with ovate to lanceolate setose scales; fronds monomorphic to weakly dimorphic, erect to arching, simply lobed to once-pinnate; stipes stramineous to dull brown, terete (lacking adaxial groove), with long and/or short unicellular to rarely septate (in Dictyocline group) hyaline acicular hairs; stipe scales ovate to lanceolate, castaneous, brown or pale, typically setose on margins and surfaces; blades membranaceous to chartaceous, drying green, olivaceous or dark brown, ovate, hastate to deltate, apex gradually reduced, never pinna-like, blades often widest at or near the base, never with several pairs of gradually reduced proximal pinnae; proliferous buds absent; pinnae entire to shallowly lobed, pinna-bases adnate (especially distally) to subsessile, bases rounded or truncate, sometimes asymmetrical, but never auricled; veins irregularly anastomosing (Dictyocline group, Fig. 4E ), forming areoles with or without included veinlets, or regularly anastomosing ( S. aspidioides , Fig. 4D ), often with several pairs of veins united below the sinus with excurrent vein running to the sinus; veins reaching laminar margins; aerophores inconspicuous or absent; indument abaxially and adaxially of stipes, rachises, costae, veins, and frequently laminar tissue between veins with long and/or short hyaline acicular hairs, these usually unicellular, occasionally with septae in the Dictyocline group; pustules absent; sori linear and coalescent along lateral and/or excurrent or irregularly anastomosing veins; indusia absent; sporangia with abundantly setulose capsules; spores morphologically coherent within the genus, with non-reticulate echinae or short wings ( Wood 1973; Tryon & Lugardon 1991; Patel et al. 2019a); x = 36, diploids and tetraploids known, three species counted. No hybrids have been reported.

Diagnosis.— Stegnogramma may be distinguished from all other Thelypteridaceae by the combination of elongate exindusiate sori, setiferous sporangia, indument on the adaxial laminae between veins, and veins irregularly anastomosing, or with at least three rows of intersegmental areoles below the sinus. The morphology of the Dictyocline group is quite distinctive within the family, with its irregularly anastomosing (pleocnemioid) venation, and laminae hastate and entire ( S. sagittifolia ), or deltate-pinnatifid ( S. wilfordii , Fig. 4E ), though these grade into somewhat more elongate laminae with up to six free pinna-pairs in the newly described Vietnamese endemic S. australis ( Chen et al. 2019) .The species of its sister genus, Leptogramma , tend to be small plants with many pairs of free pinnae, these sometimes incised halfway or more to the costae (vs. pinnae entire to crenate in Stegnogramma ), and usually with free veins, or few pairs anastomosing. The terete rachis (lacking adaxial groove) is also rare in Thelypteridaceae , shared only among the stegnogrammoids, Metathelypteris , and the three genera of Phegopteridoideae , all of which tend to have laminae more dissected than those of Stegnogramma species.

Biogeography and ecology.— The seven species of Stegnogramma occur predominantly on steep forested slopes and shaded streamsides at lower to middle elevations (to 1750 m) of the Paleotropics and subtropics. Members of the genus are most diverse in southern China, but extend from East India, Myanmar, and Vietnam north to Taiwan and Japan. A single species, the type, Stegnogramma aspidioides ( Fig. 4D ), extends into Java, Sumatra, and Borneo.

Taxonomic and phylogenetic studies.— The genus was described by Blume in 1828, based on a once-pinnate species with regularly anastomosing veins from Java. In his classification of mainland Asian Thelypteridaceae, Ching (1963) recognized Dictyocline, Stegnogramma , and Leptogramma as separate genera, including Leptogramma in tribe Thelypterideae based on its free veins, and the others in tribe Goniopterideae based on their anastomosing veins, noting the clear affinities between Dictyocline and Stegnogramma , as demonstrated by the intermediate morphology of Stegnogramma dictyoclinoides .

In his insightful treatment of these taxa, Iwatsuki (1964a, 1964b) united all three genera under a broadly defined genus Stegnogramma , which he subdivided into four subgenera, based on characters of indument and venation; Dictyocline, Leptogramma, Haplogramma , Stegnogramma . His concept of Stegnogramma was adopted by PPG I (2016). Recent phylogenetic evidence ( Kuo et al. 2019) supports the divisions proposed by Iwatsuki, with a few refinements, notably that Dictyocline is nested within Stegnogramma , and that the species of Stegnogramma plus Dictyocline are sister to Leptogramma plus a slightly revised Haplogramma. We adopt the two-genus classification proposed by Kuo et al. (2019), in which Stegnogramma (including Dictyocline) comprises seven species and is distinguished by irregularly anastomosing veins, or with regularly anastomosing veins, and three or more intersegmental areoles below the sinus. Thus defined, the genus is restricted to South and East Asia, while Leptogramma is recognized by free veins, or with up to two intersegmental areoles between main lateral veins, and is distributed in Asia, Africa, Europe, and North America.

In recent phylogenetic analyses ( Luo et al. 2018; Patel et al. 2019a; Kuo et al. 2019; Fawcett et al. in press), Stegnogramma and Leptogramma are well-supported as sister to Cyclogramma on a long branch, together forming the stegnogrammoid subclade, which diverged early within the larger cyclosoroid clade ( Fig. 1 ). The Dictyocline group ( Stegnogramma australis , S. griffithii , S. mingchegensis , S. sagittifolia , and S. wilfordii ) is subtended by a grade that includes the type, S. aspidioides , and S. dictyoclinoides ( Kuo et al. 2019; Fawcett et al. in press), rendering subg. Stegnogramma sensu Iwatsuki (1964b) non-monophyletic.

In both coalescent and concatenated analyses of a large phylogenomic dataset (Fawcett et al. in press), two Hawaiian species, treated in the newly described genus Hoiokula , are sister to the rest of the stegnogrammoid clade. However, these trees were inferred using methods that assume bifurcating evolution. Evidence from individual gene trees, and plastid loci, suggests this lineage may be of deep hybrid origin involving Leptogramma and Menisciopsis ; this hypothesis is the subject of ongoing investigation (Fawcett, Kuo, et al. in prep.).

Constituent species.—* Stegnogramma aspidioides Blume ( Fig. 4D ); * S. australis C.W. Chen & L.Y. Kuo ; * S. dictyoclinoides Ching ; * S. griffithii (T. Moore) K. Iwats. ; * S. mingchegensis (Ching) X.C. Zhang & L.J. He ; * S. sagittifolia (Ching) , L. J. He & X. C. Zhang; * S. wilfordii (Hook.) Seriz ( Fig. 4E ).

Figures

FIG.4.A.Hoiokula sandwicensis,Aborn s.n. (VT),pinna lobes,abaxial view.B.Hoiokula pendens,Hobdy2664 (UC),pinna lobes,adaxial view.C.Leptogrammapilosa, Diaz 6621 (UC), abaxial pinna lobes. D. Stegnogramma aspidioides, Palmer 1035 (UC), abaxial pinna. E. Stegnogramma wilfordii, Boufford 20159 (VT), proximal portionof lamina,abaxial view.

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