Isoetes shangrilaensis Xiang Li, Yuqian Huang, Xiaokang Dai & Xing Liu, 2019

Li, Xiang, Huang, Yuqian, Dai, Xiaokang & Liu, Xing, 2019, Isoetes shangrilaensis, a new species of Isoetes from Hengduan mountain region of Shangri-la, Yunnan, Phytotaxa 397 (1), pp. 65-73 : 71-72

Isoetes shangrilaensis Xiang Li, Yuqian Huang, Xiaokang Dai & Xing Liu , sp. nov.

Type: — China. Yunnan Province, Shangri-la 4, elevation 3305m, N 27°52′ ; E 99°44′, July 2003, X. Liu, WH2003080800 (holotype WH!) .

Diagnosis: — Isoetes shangrilaensis is similar to I. hypsophila , but different in both spore size and ornamentations: megaspore size (207.25–273.09 μm vs. 361.13–510.49 μm in I. hypsophila ), megaspore morphology (tuberculate to rugulate megaspore vs. laevigate megaspore in I. hypsophila ), and microspore morphology (echinate to cristate microspore vs. bacculate to rugulate microspore in I. hypsophila ).

Description: —Plants aquatic, submersed. Root stock 3-lobed. Leaves white basally, green above, spirally arranged, wide spreading, 28.51–178.42 mm long, ca. 1 mm wide at mid-length, in tufts of 12 to 20, flatted on upper side, rounded on lower sides, base alate; ligule triangular, cuspidate; velum rudimentary, covering only distal edge of sporangium. Sporangium basal, oval, ca 1.3–5.6 x 1.7–4.5 mm. Megaspores, 207.25–273.09 μm in diameter (mean 244.71 μm); proximal surface laevigate with some scurfy scales, globose in the polar view while less oblate in equatorial view; equatorial and radial ridges thin and smooth; distal surface low, sparsely tuberculate to rugulate but crowdedly covered with small fibrils. Microspores, 11.21–23.66 μm in length (mean 19.41 μm); proximal surface coarsely low echinate to cristate surface with occasional filamentous structures; proximal ridge not clear and without swellings perpendicular to it; distal surface similar as proximal surface, echinate to cristate.

Distribution and habitat: — Isoetes shangrilaensis can be considered endemic to Shangri-la in Yunnan Province, and it is currently detected only in two localities, Xiajisha Country and Caishichang. The plants are submersed in the ponds. Isoetes shangrilaensis is a rare and endangered species in China. We have found only two sites in Shangri-la in Yunnan Province. Pollution continues to raise the risk of extinction for this species. The protection of two populations of this new species of Isoetes are crucial, and search for additional populations are urgently needed.

Additional specimens examined: — China. Yunnan Province, Shangri-la, Xiajiasha country, elevation 3275m, N 27°28′ ; E 99°48′, July 2010, X. Liu, WH2010 (holotype WH!) .