Botanical survey identifies new Argostemma species in Hainan

A botanical taxonomic study has identified Argostemma baotingense as a new species of Argostemma in the family Rubiaceae. The plant was discovered during a field survey in March 2025 in the forest valleys of Tonganling Mountain on Hainan Island, southern China. The authors describe it as a lithophytic herb known from a single population and recommend classifying it as Data Deficient under the IUCN Red List criteria because its broader distribution has not been investigated.

The survey involved fieldwork, examination of herbarium specimens, consultation of relevant literature and morphological comparisons with previously known members of the genus. Specimens were collected from rocks in a forest valley in Baoting County, Hainan, and living plants were introduced to the nursery of the Tropical Crops Genetic Resources Institute of the Chinese Academy of Tropical Agricultural Sciences. Habitat information was recorded during the field surveys, while morphological observations and measurements were made on living plants both in situ and ex situ.

Type specimens were deposited in the herbaria of the Tropical Crops Genetic Resources Institute of the Chinese Academy of Tropical Agricultural Sciences and the South China Botanical Garden. The holotype was collected on 30 May 2025 at an elevation of 730 m in the valleys of Tonganling Mountain, Baoting County. It has the collection number DSP202503, and the isotypes are recorded as IBSC1104113 and IBSC1104114.

Argostemma baotingense is described as a glabrous, suberect or creeping herb with a stem 5–15 cm tall and approximately 3 mm in diameter. Its leaves are opposite and slightly anisophyllous, with linear blades measuring 1.1–5 × 0.3–0.6 cm. The adaxial surface is glossy and dark green, with strigose hairs on the midrib and sometimes near the margins, whereas the abaxial surface is glabrous and described as greenish white to silvery white.

The terminal inflorescence is white, glabrous and one- or two-flowered, with four persistent, glabrous bracts. The calyx has five light-green, triangular lobes, each about 3 mm long. The white, rotate corolla is glabrous, with a tube about 2 mm long and five lanceolate lobes measuring 10–12 × 4–5 mm. Five stamens are about 8 mm long, with coherent yellow anthers that open by longitudinal slits. The style is about 9 mm long and ends in a columnar stigma approximately 0.5 mm long.

The authors identify A. baotingense as morphologically similar to A. bachmaense T.V.Do, but the new species has a suberect or creeping stem rather than an erect one, linear leaves rather than oblanceolate to spatulate leaves, and a glabrous inflorescence and calyx rather than pubescent ones. The comparison also records differences in stipules, bracts, sepals, stamens and stigma. The new species can additionally be distinguished from the other two Argostemma species recorded in Hainan: A. discolor, known from Wuzhishan, Diaoluoshan, Bawangling and Jianfengling, has elliptical leaves and a hairy calyx, while A. hainanicum is known only from its type locality at Jianfengling and differs in leaf shape and indumentum.

The treatment includes a key for identifying the nine Argostemma species recognized in China. Before the description of A. baotingense, eight species had been recorded from Guangdong, Hainan, Yunnan, Guangxi and Taiwan. The new species was observed flowering from May to June. Its name derives from Baoting County, its type locality, and its Chinese name is 保亭雪花, pronounced bǎo tíng xuě huā.

Only one population of A. baotingense has been found, in the valleys of Tonganling Mountain forest. The authors report that the population is relatively large and that the plant can reproduce asexually through its stems. They caution that the species may occur elsewhere, but state that its wider distribution remains uninvestigated and recommend Data Deficient status under the IUCN Red List criteria.

Living material from the type locality is currently cultivated at the nursery of the Tropical Crops Genetic Resources Institute. The authors also describe the plant as having ornamental value and consider it suitable for cultivation in rainforest eco-tanks. These horticultural observations accompany a taxonomic description based on a single known population; the study does not provide a broader population survey or a full assessment of the species’ distribution across Hainan or elsewhere in China.

Subject of Research: Taxonomic description of a new Argostemma species from Hainan Island

Article Title: Argostemma baotingense ( Rubiaceae ), a new species from Hainan Island, South China

Article References: Dong, S.-P., Yuan, L.-X., Wang, Q.-L., & Yang, H.-B. (2026). Argostemma baotingense (Rubiaceae), a new species from Hainan Island, South China. PhytoKeys, 276, 253-260. https://doi.org/10.3897/phytokeys.276.195404

Image Credits: AI Generated

DOI: 10.3897/phytokeys.276.195404

Keywords: Argostemma baotingense, new species, plant taxonomy, Rubiaceae, Hainan Island, Tonganling Mountain, flora of China, morphological analysis, lithophytic herb, Data Deficient, Argostemma, baotingense