Bredia bullata, B. enchengensis, and B. nitida (Sonerileae, Melastomataceae), three species occurring in Sino-Vietnamese limestone karst regions, are described as new. Molecular phylogenetic analyses and morphological divergence indicate that these species are well separated from their close relatives in Bredia, justifying their recognition as distinct species. Bredia bullata is unique in its interveinal areas prominently bullate each with an apical seta, a character otherwise never recorded in the genus. Bredia nitida resembles B. malipoensis in habit, leaf shape, and inflorescence morphology, but differs in the glabrescent and nitid adaxial leaf surface (vs. densely pubescent and subvelvety), ovate-elliptic or elliptic calyx lobes (vs. triangular to semiorbicular), and white petals (vs. purplish-red). Bredia enchengensis is closest to B. longiradiosa, but easily recognized by its prostrate habit (vs. erect), the yellowish-green, membranous and fragile leaves (vs. green or dark green, papery), and white anthers (vs. pink to purplish). These new discoveries show that further botanical exploration is warranted in the remote Sino-Vietnamese bordering region.

A new species, Oreocharis tetrapterus F.Wen, B.Pan & T.V.Do (Gesneriaceae) from Gupo Mountain area, Hezhou city, Guangxi Zhuangzu Autonomous Region, China, is described and illustrated. The new species has a zygomorphic tetramerous corolla with two adaxial and two abaxial lobes and two fertile stamens in the posterior position, making this a unique combination of floral characteristics in the expanded Oreocharis.

Aristolochia quangbinhensis T.V. Do, a new species from Central Vietnam, is described and illustrated. According to morphology, the species belongs to Aristolochia subgenus Isotrema. A detailed description, along with line drawings, photographs, ecology, distribution, conservation status as well as a comparison to morphologically similar species is provided.

Perilimnastes is a genus currently treated in the polyphyletic Phyllagathis. Recent phylogenomic analyses have identified a morphologically cohesive lineage referred to as the Phyllagathis (raphides) clade, which should be excluded from Phyllagathis and treated as a distinct genus under the name Perilimnastes. Morphological and phylogenomic data have confirmed that four new species collected from Vietnam are part of the Phyllagathis (raphides) clade. They are described herein as Perilimnastes multisepala, P. setipetiola, P. uniflora, and P. banaensis. Perilimnastes multisepala is phylogenetically closest to Phyllagathis setotheca, and morphologically to P. fruticosa and P. stenophylla, but is distinct in the 4- to 8-lobed calyx, 28 × 9 mm, apically long acuminate petals, and 1–2 mm pedicel at fruiting stage. Perilimnastes setipetiola, P. uniflora, and P. banaensis are phylogenetically most closely related. Perilimnastes uniflora is characterized by its prostrate habit, small size, glabrous, obovate to obovate-lanceolate leaf blade, and solitary flower. Perilimnastes setipetiola and P. banaensis resemble each other in habit, leaf size and shape, and sessile or near sessile inflorescences but can be easily distinguished by the indumentum of the stems and leaves.

This is the third paper in a series dedicated to updating the knowledge of the Vietnamese pteridophyte flora. Based on recent collections, we first reported three new national records of ferns: Haplopteris yakushimensis, Lindsaea kohkongensis, and Pteris pseudowulaiensis. Secondly, we conducted phylogenetic analyses to investigate the placements of Lindsaea kohkongensis and Leptochilus poilanei, each based on three plastid DNA markers. Our results revealed that Lindsaea kohkongensis is sister to L. ensifolia, while Leptochilus poilanei is embedded within L. cantoniensis. We discussed these results in the context of systematics. Lastly, we reported chromosome numbers for 20 fern species in Vietnam. For seven of these species, including Gymnosphaera salletii, Lepisorus spicatus, Leptochilus poilanei, Pteridrys costularis, Pteris latipinna, Pyrrosia eberhardtii, and Tectaria setulosa, these counts were recorded for the first time. Additionally, three new cytotypes were identified for Diplazium doederleinii, Pteris esquirolii, and Tectaria harlandii. This study underscores the need for more diverse data, including DNA sequences, chromosome numbers, and reproductive modes, to be collected and integrated into systematic studies and taxonomic treatments to enhance our understanding of Vietnam’s pteridophyte flora.