Isoetes yuhangensis X. Liu & Y.C. Chen, sp. nov. (Figure 2)

Diagnosis: — Isoetes yuhangensis differs from I.taiwanensis by its rugulate megaspores with fibrous perispores (vs tuberculate megaspores), velum absent (vs velum rudimentary), semicircular labium (vs reniform labium), and the megaspore muri connected on the distal surface (vs megaspore muri rarely connected).

Type:— CHINA. Zhejiang Province, Hangzhou City, Yuhang District, Huanghu Town, Cibi Village, elevation 81 m, 30°26′52″ N; 119°50′22″ E, 27 September 2021, X. Liu, WH2021092702 (holotype WH!) .

Description: —Plants aquatic, amphibious, growing among paddy field drainage ditch. Corm 3-lobed. Roots conspicuous, dichotomously branched. Leaves white basally, green above, 1.1–2.3 mm wide at middle, 12–32 cm long, 5.7–10.6 mm wide at the base, erect to ascending, apex acute to attenuate. Ligule triangular. Labium present, semicircular. Sporangium 9.4–11.4 mm long, 4.2–5.8 mm wide, basal, oblong, the surface of sporangium with white, and membranous. Velum absent (Figure 2G and 2H). Megaspores, 270–324 µm in diameter (N = 30 +/- SD 14.0 µm); proximal surface rugulate; equatorial ridges thin and corrugate, radial ridges thick and smooth; distal surface rugulate and densely covered with fibrous perispores (Figure 2A–C). Microspores, 16–26 µm in length (N = 30 +/- SD 2.3 µm), monolete, proximal and distal surface sharp-tipped echinate (Figure 2D and 2E). Chromosomes: 2n = 22 (Figure 2F).

Etymology: —The specific epithet refers to the type locality Yuhang district, Zhejiang, where this species is endemic.

Distribution and Habitat: — Isoetes yuhangensis is only known from one locality, Cibi village (Figure 6). The plants are located at the bottom of the mountain (Figure 2I), which are dominated by Metasequoia glyptostroboides Hu & W. C. Cheng, and associated with Alisma canaliculatum A. Braun & Bouché, Limnophila sessiliflora (Vahl) Blume, Lysimachia clethroides Duby, etc. Isoetes yuhangensis is a rare and endangered species in China. We have found only one site in the Yuhang district. It is vital to protect the populations of these new Isoetes species, and there is an urgent need to find additional populations.