Carex yankouensis, a new species of Cyperaceae (Carex section Rhomboidales) from the limestone landform in northern Guangdong, China is described and illustrated. The new species is similar to C. brevicuspis C. B. Clarke, but differs in having shorter culms (10–15 cm vs 20–55 cm) and spikes (1–1.5 cm vs 3.7–7 cm), leaves wider (15–20–35 mm vs 5–10 mm) and lighter colored (pale green or yellow-green vs dark green), nutlet beak oblique (vs erect or slightly curved), and slightly thickened (vs thickened) style base. Following the IUCN Red List Criteria (IUCN 2024), Carex yankouensis is assessed as ‘Data Deficient (DD)’.

Carex, limestone landform, new species, taxonomy

Carex L., belonging to Cyperaceae, encompasses approximately 2000 species which are distributed across all continents except Antarctica. Notably, the treatment in Flora of China features 527 of these species, with an impressive 260 being exclusive to China (Dai et al. 2010). Undoubtedly, Carex stands as one of the most diverse genera among seed plants worldwide, yet the intricacies of its classification pose significant challenges. Despite these difficulties, recent years have witnessed the publication of numerous novel Carex species for China (Li et al. 2022; Lu and Jin 2022; Lu et al. 2023; Li et al. 2024; Qiu et al. 2024) and other parts of the world.

In Flora of China (Dai et al. 2010), species of the genus Carex are classified into 42 sections and three subgenera. The treatment includes section Rhomboidales with 43 species. However, the taxonomic revisions of the section have not been entirely resolved yet. Jin and Zheng (2013) revised this section and recognized 40 species, along with six subspecies and four varieties, but due to the widespread distribution of the species of this section, new species may still exist in some special geomorphic areas, such as limestone regions. Indeed, some recently published species of this section, such as C. duanensis Z.C.Lu, Y.F.Lu & X.F.Jin (Lu et al. 2024), are distributed in such limestone landform areas.

In July 2021, during our investigation in the limestone area of northern Guangdong, we collected a distinct species of Carex which they grew on the walls of a karst cave. Although it neither bloomed nor bore fruit, the specimens were striking by their wide leaves, which reached a width of up to 35 mm, and the obvious small transverse veins between the leaf veins. We took two plants back to Changsha City for further observation and research. Fortunately, in November of that year, these two plants bloomed and provided us with mature nutlets for our research in March of the following year. At the same time, we also went to the corresponding phenological period to collect voucher specimens from the type locality. Through phenological observation and morphological research, we finally confirmed that this was a new species of C. sect. Rhomboidales.

The specimens are mainly stored in the Herbarium of Forest Plants in Central South University of Forestry and Technology (CSFI). The morphological observation of the new species is based on field investigations, cultivated plants from the type locality, and specimen studies. Morphological research includes the length of rhizomes, the length, width and color of leaves, number of spikes, and the shape, size of bracts, glumes, utricles, and nutlets. We also use SEM to observe the nutlets which come from the holotype specimen we collected to ensure that the relevant descriptions were true. The sample preparation process and operating procedures of SEM refer to previous research by Lu et al. (2024). The conservation status of this new species is based on field observations in accordance with IUCN Red List guidelines (IUCN 2024).

Thanks for PhD Jing Tian’s exquisite preparation of the line drawing and constructive opinions from reviewers and editors.