Asplenium paucipinnatum (Aspleniaceae), a new fern species from southern Thailand, based on morphological and molecular data

Asplenium paucipinnatum, a new fern species from Nakhon Si Thammarat, Thailand, is described. Morphologically, it closely resembles A. micantifrons in having short-creeping and radial rhizome steles, 1 - pinnate laminae, deeply incised pinnae on the basiscopic margin, and sori arranged in two rows close to the costae. However, A. paucipinnatum is readily distinguished by having fewer lateral pinnae (<14 pairs), obliquely rhombic pinnae with acute apices and obtuse marginal teeth, contrasting the more numerous pinnae (> 15 pairs), lanceolate pinnae with acuminate apices, and acute teeth in A. micantifrons.

Phylogenetic analyses based on multiple plastid DNA regions (atpB, rbcL, rps 4, rps 4 - trnS, trnL, and trnL-F) support A. paucipinnatum as a distinct lineage, forming a sister relationship with a clade containing A. lepturus and A. contiguum. The combination of morphological and molecular evidence supports the recognition of this new taxon. Ecological notes, geographic distribution, and a comparison with related species are also provided.