Thalictrum yambaruense Michim., Yokota & S. Fujii 2025, sp. nov.

Thalictrum yambaruense Michim., Yokota & S.Fujii, sp. nov. Diagnosis: Similar to Thalictrum watanabei, this species differs in having pedicels shorter than 5 mm (vs. 10–15 mm in T. watanabei). Sepals are approximately 2 × 1 mm (vs. 3–4 × 1.5–2 mm). Pistils are not bent or are slightly bent (vs. strongly bent (Table 1; Figs. 2 & 3). Holotype: JAPAN, Okinawa Prefecture: Okinawa Island, Kunigami-gun, Kunigami-son, Aha. 16 April 2022, A. Abe, M. Yokota, T. Ito, K. Michimoto, T. Nakasone, S. Higa & J. Shinjo 2095 (OCF). Description: Herbs, perennial, glabrous, up to 20 cm tall. Roots tuberous. Stems simple or few branched. Basal leaves 3–5; leaf blade 1- or 2-ternate; leaflets broadly ovate or orbicular, herbaceous, abaxially greenish white, 1–1.8 × 1–1.5 cm, apex 3-lobed; petiole 2–5cm. Inflorescences cymes with 2–15 flowers. Flowers 0.3–0.5 cm in diam.; pedicels less than 5 mm. Sepals 3–4, persistent, white, elliptic, ca. 2 × 1mm. Stamens white, 2–4mm; filament base filiform, apex oblanceolate, same as broad as anther. Carpels 5–10; style not bend or bend slightly, stigmas lanceolate. Achenes stipe ca. 0.5 mm, body fusiform, compressed, ca. 2 mm. Distribution and habitat: Known only from the type locality in the Yambaru region. The upper reaches of the river basin consist of well-preserved mountain streams in natural forest stands (Kyushu Regional Forest Office, 2000). The species grows on dripping cliff faces. Etymology: The specific epithet “yambaruense ” refers to the type locality, the Yambaru region. Japanese common name: Yambaru-karamatsu (nov.). Paratypes: JAPAN, Okinawa Prefecture: Okinawa Island, Kunigami-gun, Kunigami-son, Aha. 16 April 2022, Takuro Ito 7857 (TUS). 29 August 1994, M. Yokota 10369 (RYU). Conservation status: Thalictrum yambaruense is known from a single population, exclusively located in the upper reaches of the Yambaru region in northern Okinawa Island (Yokota et al. 1997). It is classified as a critically endangered species (Category IA, CR), similar to Thalictrum minus (Okinawa Prefectural Department of Environmental Affairs 2018). The total number of mature plants or ramets is estimated to be fewer than 50, classifying it as a critically endangered species IA (CR) according to the IUCN Red List Categories and Criteria “D” (IUCN 2000). A water storage dam built in the lower reaches may have eradicated unknown populations downstream.