Type: — CHINA. Xizang: Jiacha Co., 5200 m, 22 July 2012, S. Y. Meng et J. Q. Zhang 120722-10 (holotype, PEY!). China. Xizang: Longzi Co., 5043 m, 22 July 2013, S. Y. Meng B 1702, S. Y. Meng B 1701 (paratype, PEY!)

Diagnosis: —Dioecious, 1–5 cm high. Caudex leaves dimorphic: triangular-ovate to very broadly triangular and long-linear. Flowering stems 3–10, erect, simple. Stem leaves alternate, sessile, linear to linear-lanceolate, entire. Inflorescences terminal, often solitary flower. Flowers 3-merous; Sepal (♀) yellow-green; Petals free, pink, green at the base, triangular (♀). Follicles erect, blackish red at maturity; seeds 3–4, winged on one side.

Description:— A perennial herb, dioecious, 1–5 cm high. Caudex cylindrical, 3–7 mm thick, 8–40 mm long, erect; the apical part densely covered with scaly radical-leaves. Scaly radical-leaves chartaceous, persistent, triangular-ovate to very broadly triangular with entire margin, acute-acuminate at the apex, 3–5 mm long, 1–3 mm wide, blackish brown. Flowering stems 3–10 from each branch apex of rhizomes, deciduous, 5–12 mm long, 0.2–0.3 mm thick, erect, simple, terete, glabrous; persistent old flowering stems like a long scaly radical-leaves, but with a big midrib, long-linear, 5–7 mm long, 0.2–0.4 mm wide. Leaves alternate, rather densely arranged on the upper part, ascending-spreading, sessile, spurless, thick herbaceous, flattish, yellowish green, linear to linear-lanceolate; acute-acuminate at the apex; very short attenuate at the base; entire along the margin, 4–5 mm long, 0.8–1 mm wide, glabrous on both surfaces; the costa not obvious. Every flowering stem with 1 (–3) flowers, scarcely bracteates (♀), bracts leafy, linear to linear-subulate, round (-acute) at the apex, 4–4.5 mm long and 1 mm wide. Flowers 3-merous, 3–5 mm acoss at anthesis, pedicellate; the pedicel 1–3 mm long, laevis. Sepal (♀), yellow-green, glabrous, laevis, freely; the lobes triangular, acute-obtuse at the apex, 1.6–2mm long, 0.3–1.2 (–1.4) mm wide, entire along the margin, flattish, erect-suberect at anthesis. Petals free, pink, green at the base, triangular (♀), obtuse-acute at the apex, 1–1.4 mm (♀) long, 0.6–0.8 mm (♀) wide, entire along the margin, laevis, spreading at anthesis. Nectar-scales oblong, truncate at the apex, 0.2–0.4 mm long, 0.4–0.6 mm wide. Gynoecia 2–3 mm (♀) long at anthesis; ovaries basally ca. 0.1 mm connate, ventrally straight, 0.4–0.6 mm (♀) wide; the style very short, indistinguishable from the ovaries, ca. 0.1 mm long, holed at the apex. Ovules ca. 3–4 (♀) in each locule, ca. 0.4 mm long. Follicles erect, ca. 2.5 mm, 0.8–1 mm diam., connective ca. 0.1 mm in base, beak straight, ca. 0.5–0.6 mm, blackish red at maturity; seeds 3–4, one side with winged, 0.8 mm long, 0.3 mm wide. See Figs 5 and 6.

Habitat: —Perennial herbaceous on humid and with more soil of mountain ridges, summits of mountains, 5000–5200 m.

Phenology: —Flowers from July to August; fruits from August to October.

Distribution: —The distribution of Rhodiola tricarpa has been found only in the summit of mountains in Jiacha County, Qusong County, Longzi County, Xizang (Tibet) China.

Etymology:— Flowers 3-merous, three carpel per flower, diffrent from all other species of this genus which are 4-or 5-merous.

Notes: —Because of dioecy, with persistent old flowering stems and elongate flower stems indicated the close relationship of this new species with ones of section Chamaerhodiola, but distinct from other species of this section in flower morphology (3-merous vs 4- or 5-merous) and persistent old flowering stems. According to the ITS data (Fig. 1) and cpDNA data (Fig. 2), R. tricarpa shared affinity with R. coccineae, R. fastigiata and R. tangutica, although there is not well separated by cpDNA. R. tricarpa and R. coccineae have same habitat(summits of mountains), but different in the former with 10–50 mm stem, 3-merous flowers, greenish sepal and pink petal. R. tricarpa and R. fastigiata share same triangular caudex leaves and greenish sepal, but different in the former with shorter stems (10–50 mm vs more than 500 mm), more simple inflorescence (1–3 flowers vs corybiform-paniculate), 3–merous and shorter fruit (2.5 mm vs 7–8 mm). R. tricarpa and R. tangutica have same triangular caudex leaves, pink petal, different in the former with 3-merous, small value of length of petal/length of sepal (0.7 vs 1.285) and shorter fruit (2.5 mm vs 7–8 mm). The detailed comparison of several morphological characters between them is listed in Table 4.