Thalictrum hengduanshanense Y. P. Zeng, Q. Yuan & Q. E. Yang, 2022

Zeng, You-Pai, Yuan, Qiong & Yang, Qin-Er, 2022, Thalictrum hengduanshanense and T. longistipitatum (Ranunculaceae), two new species from southeastern Xizang and northwestern Yunnan, China, Phytotaxa 571 (1), pp. 1-20 : 6

Thalictrum hengduanshanense Y. P. Zeng, Q. Yuan & Q. E. Yang , sp. nov. (Figs. 1, 5, 6).

Type:— CHINA. Yunnan: Dêqên, Yunling town , on the way from Xidang spring to Yubeng village , in dry forests on slopes, alt. 2920 m, 11 July 2021, Y.P. Zeng & Y.F. Luo 530 (holotype IBSC, barcode unavailable; isotypes KUN, PE, barcodes unavailable). Fig. 6 .

Diagnosis:— Thalictrum hengduanshanense is most closely related to T. tsawarungense , but differs by having laxly branched, corymb-like (vs. narrowly paniculiform) inflorescences and larger (ca. 9 mm vs. 4.5‒7 mm long), narrowly lunate (vs. broadly lunate) achenes (body width/body length = ca. 1/3 vs. ca. 1/2).

Description:—Perennial herbs. Roots fibrous. Stem 30‒60 cm tall, distally branched, glandular-pubescent. Leaves 2‒3-ternate; blade triangular, 5‒10 cm long, 4‒10 cm broad; leaflets broadly obovate, obliquely broadly obovate, suborbicular or broadly ovate, 0.5‒1.5 cm long, 0.5‒1.5 cm broad, herbaceous, both sides densely glandularpubescent, adaxially green and abaxially pale green, base rounded or subcordate, apex obtuse or acute, 3-lobate; lobes entire or 1‒2-crenate, apex obtuse or acute; veins submerged adaxially, raised abaxially; petioles glandular-pubescent, 1‒3 cm long; stipules sheath-like or free, obliquely broadly ovate, membranous, margin wavy. Inflorescence a panicle, laxly branched, corymb-like, glandular-pubescent. Pedicels 1‒1.5 cm long, glandular-pubescent. Flowers bisexual. Sepals 4 or 5, broadly elliptic or ovate, 2.5‒3 mm long, 2‒2.5 mm broad, abaxially sparsely glandular-pubescent, whitish or tinged with pinkish; basal nerves 3‒5, simple or branched. Stamens ca. 16, 3‒5 mm long; filaments narrowly oblanceolate-linear, 2.5‒4 mm long, white; anthers narrowly oblong, 0.6‒0.8 mm long, ca. 0.4 mm broad, apex obtuse, white. Carpels 2‒6, ca. 3 mm long, glandular-pubescent, stipitate, whitish tinged with purplish; stipe ca. 0.4 mm long; ovary obliquely narrowly obovate, ca. 1 mm long; style ca. 2 mm long, straight or apically slightly recurved; stigma inconspicuous. Achenes ca. 9 mm long, glandular-pubescent, long stipitate, pink when fresh; stipe ca. 2 mm long; body narrowly lunate, body width/body length ca. 1/3, shallowly ribbed, compressed; style persistent, apically slightly recurved. 2 n = 14.

Phenology:—Flowering from June to August; fruiting from July to September.

Distribution and habitat:— Thalictrum hengduanshanense is currently known only from the southern Hengduan Mountains region in southeastern Xizang (Zayu) and northwestern Yunnan (Dêqên, Weixi), China (Fig. 13). It grows in mixed conifer-broadleaved forests on slopes, hot dry valleys or along open streamside at elevations of 1900‒3100 m above sea level. The Hengduan Mountains region, which is at the end of the eastern Himalayan range in southwestern China, includes mainly southern Gansu, southeastern Qinghai, western Sichuan, southeastern Xizang, and northwestern Yunnan. Steep gorges and high peaks dominate this region, which is recognized as a biodiversity “hotspot” ( Boufford & van Dyck 1999, Myers et al. 2000), and harbors the richest temperate flora of seed plants in the world ( Wu 1988, Li & Li 1993, Luo et al. 2016, Liu et al. 2021).

Etymology:—The specific epithet of this new species, “ hengduanshanense ”, is derived from the southern Hengduan Mountains region (“shan” means “mountain” in Chinese), where the new species occurs.

Additional specimens examined (paratypes):— CHINA. Xizang: Zayu, Anonymous 75 (HITBC, herb. no. 083724), SE Xizang Exped. 147 (PE02283031, PE02283032, PE02283033). Yunnan: Dêqên , K.M. Feng 5214 (KUN0690082, KUN0690093, KUN0690504, PE00450029,) , Qinghai-Xizang Exped. 1846 (CDBI0026439, CDBI0026440, HITBC, herb. no. 003380, KUN0690106, PE01108989, PE01108990) , Qinghai-Xizang Exped. 2589 (CDBI0026441, PE01108991) , L. Xie & J.F. Mao 133 (PE01569465) , L. Xie & J.F. Mao 134 (PE01569409) , L. Xie & J.F. Mao 135 (PE01569410) , J.S. Yang s.n. (KUN0690094) , T.T. Yu 8264 (KUN0690101, KUN0690500, PE00450025) ; Weixi, K.M. Feng 4833 (KUN0690084, KUN0690085, KUN0690086) .

Conservation status:— Thalictrum hengduanshanense is currently known only from four populations in southeastern Xizang (Zayu) and northwestern Yunnan (Dêqên, Weixi), China. The Dêqên population we discovered recently consists of more than 300 individuals. The size of the Zayu and Weixi populations remains unknown. The conservation status of T. hengduanshanense should therefore be considered as “Data Deficient (DD)” before adequate information of this species is acquired ( IUCN Standards and Petitions Committee 2019).