Researchers have recently identified a striking new fern species, Polystichum ensiforme, in the lush subtropical forests of Guangxi, China. This discovery underscores the region’s status as an underexplored biodiversity treasure trove, renowned for its karst landscapes and rich flora.

The new fern species Polystichum ensiforme (P. ensiforme) is named for its sword-shaped fronds. It is an evergreen fern, reaching 30-50 cm tall.

It is morphologically most similar to Polystichum basipinnatum (P. basipinnatum) in having linear-lanceolate laminae that are simple and occasionally divided. It differs from all other Cyrtomidictyum species by rarely exhibiting pinnatifid laminae, which are confined in a few fronds bearing a whip-like apex at the rachis tip. When pinnatifid laminae are present, all segments are exclusively rounded. It further differs in having sori irregularly scattered along both sides of the rachis and distinctly thick, leathery laminae.

By plastid genome sequencing of 15 samples across five related species, the researchers found 161 unique genetic variants and a distinct microsatellite allele. Phylogenetic trees showed P. ensiforme forms a monophyletic clade with 100% support, sister to four known Cyrtomidictyum species.

P. basipinnatum thrives on streamside rocks near waterfalls at elevations of 200–600 meters. It is endemic to China and currently only found in Guangxi (Guilin, Yangshuo, Rongxian) and Guangdong (Ruyuan, Yangchun, Zhaoqing, Jiangmen). Its restricted range highlights the urgency to protect these ecosystems.

The study, published in Phytotaxa, was completed by researchers from Shanghai Chenshan Botanical Garden, Institute of Botany and Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences, and others.

Morphological comparison between Polystichum ensiforme (top) and P. basipinnatum (bottom)