Leptogramma

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 49-50

LEPTOGRAMMA

Leptogramma J. Sm., J. Bot. (Hooker) 4:51.1842.

— LECTOTYPE (designated by Christensen,Ind.Fil.xxi.1905): Leptogramma totta (Schltdl.) J. Sm. [= Gymnogramma totta Schltdl. ]— Thelypteris sect. Leptogramma (J.Sm.) C.V.Morton

Craspedosorus Ching & W. M. Chu

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

Etymology.— Gr. lepto, slender + gramme, line, in reference to the linear sori on the veins ( Stewart et al. 1983).

Plants terrestrial or epipetric, of tropical and subtropical forest understories, streamsides and rocky banks, mostly small (10–50 cm); rhizomes short-creeping to erect, with ovate to lanceolate setose scales; fronds monomorphic to weakly dimorphic, erect to arching, pinnate to pinnate-pinnatisect; stipes stramineous to dull brown, terete (may not be visible upon drying), with long and/or short unicellular or multicellular 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, hastate, ovate to lanceolate, apex gradually reduced, never pinna-like, blades often widest at or near the base, never with many pairs of gradually reduced proximal pinnae; proliferous buds absent; pinnae typically shallowly to deeply lobed, sometimes entire ( L. cyrtomioides ) to pinnatisect ( L. sinensis ), pinna-bases adnate (especially distally) to short-petiolulate proximally, rounded or truncate, sometimes asymmetrical, but not strongly auricled; veins free, mostly simple to sometimes forking, or, if anastomosing (in sect. Haplogramma), then two pairs or fewer meeting below the sinus at an acute angle; veins reaching laminar margins, or terminating before (e.g., L. tottoides ); aerophores inconspicuous or absent; indument abaxially and adaxially of stipes, rachises, costae, veins, and laminar tissue between veins with long and/or short hyaline acicular hairs, these unicellular (sect. Leptogramma ) or multicellular (sect. Haplogramma); pustules absent; sori linear to slightly elongate along ultimate veins ( Fig. 4C ); indusia absent; sporangia with setulose capsules; spores echinate ( Wood 1973; Tryon & Lugardon 1991), except in L.pozoi , which has broad wings similar to spores of Cyclogramma ( Patel et al. 2019a) and one population of L.pilosa , in which the echinae anastomose into loops ( Watkins & Farrar 2005); x = 36, diploids, triploids, and tetraploids known, eight species counted.

Diagnosis.— Leptogramma may be recognized by the combination of elongate exindusiate sori, setulose sporangia, and long hyaline acicular hairs on the adaxial laminae between veins. It is distinguished from its sister genus Stegnogramma by veins free, or if anastomosing, only one or two pairs united below the sinus between adjacent lateral veins (vs. usually three or more), and by the presence of long multicellular hairs on rachises.

Biogeography and ecology. —The 29 species of Leptogramma are most diverse in the Himalayan region, with numerous endemics in southern China, occurring from lower elevations up to 2700 m. Within Asia, species extend north to Japan, west and south to Sri Lanka, and into eastern Malesia, including the Philippines, Java, and Sulawesi.One species, L. totta , is native to South and East Africa, another, L. pozoi , to southern Europe and North Africa; two are endemic to North America— L. pilosa in Mexico and Central America, and L. burksiorum , in Alabama, in the southeastern United States ( Watkins & Farrar 2005). They occur in shady forest understories and disturbed forest edges, or on rocky banks or cliffs, especially limestone.

This genus is unusual among tropical genera of the Thelypteridaceae for having such a broad amphioceanic tropical or subtropical distribution coupled with many local endemics. Other comparable groups include Christella , which is predominantly continental Asian with two native species in the Neotropics, or Amauropelta , which is most diverse in the Andes and Central America but has secondarily dispersed to Africa and several Pacific and Atlantic islands. Two genera, Cyclosorus and Strophocaulon , have diversified little, but are widely distributed in lowland tropics. Essentially all other genera are more regionally restricted.

Taxonomic and phylogenetic studies. —John Smith’s (1842) original concept of Leptogramma included a diverse group of ferns with linear sori, including species now recognized in Amauropelta, Athyrium , and Sphaerostephanos . Ching (1936, 1963) united most of the species we recognize today in his concept of Leptogramma , which was treated within a broadly defined Stegnogramma by Iwatsuki (1964a, 1964b). The Flora of China ( Lin et al. 2013) recognized Ching’s genera Stegnogramma , Leptogramma , and Dictyocline, plus the monotypic Craspedosorus, while PPG I (2016) adopted a broad concept of Stegnogramma , including all of these genera. With the recent publication of a densely sampled phylogeny—the first to include the type of Stegnogramma — Kuo et al. (2019) chose to recognize a two-genus system, although either Leptogramma s.s. plus Stegnogramma s.s. or Stegnogramma s.l. is monophyletic. We adopt their classification here. For additional discussion, see our treatment of Stegnogramma .

Leptogramma can be divided into two sections, sect. Leptogramma and sect. Haplogramma, which are recognized by Kuo et al. (2019) and correspond closely to the infrageneric classification of Stegnogramma proposed by Iwatsuki (1964a, 1964b) with only minor revisions. Section Haplogramma is strictly Asian, and is recognized by septate hairs along the stipes, whereas sect. Leptogramma has a wider distribution (including Europe, Africa,and North America) and unicellular (vs. septate) hairs on stipes ( Kuo et al. 2019). The species within this section tend to be smaller, with more deeply lobed pinnae, and with exclusively free veins. Most necessary combinations in Leptogramma and Stegnogramma have been made by Kuo et al. (2019), and we adopt their taxonomic concept here, including the inclusion of the monotypic genus Craspedosorus within Leptogramma .

Historically, the name Leptogramma pozoi had been broadly applied to plants of both Europe and East Asia, but that taxon is now recognized as restricted to southern Europe and northern Africa, with Asian plants now treated as L. mollissima ( Kuo et al. 2019) . However, considerable complexity in geographic, morphological, and ecological variation has been demonstrated within these taxa ( Yatabe et al. 1998), as well as within the neotropical Leptogramma lineages ( Watkins & Farrar 2005). Further detailed study of these groups may uncover unrecognized diversity deserving of species status.

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.