Hydrostachys flabellifera G.W. Hu, Zhun Xu & Q.F. Wang, 2020

Xu, Zhun, Tian, Jing, Rapanarivo, Solo Hery Jean Victor, Letsara, Rokiman, Rakotonasolo, Rivontsoa A., Onjalalaina, Guy E., Hu, Guang-Wan & Wang, Qing-Feng, 2020, Hydrostachys flabellifera (Hydrostachyaceae), a new species from Madagascar, PhytoKeys 167, pp. 45-56 : 45

Hydrostachys flabellifera G.W. Hu, Zhun Xu & Q.F. Wang sp. nov. Figs 1 , 2

Diagnosis.

Hydrostachys flabellifera is similar to H. verruculosa and H. laciniata in having simple leaves, but it can be easily distinguished from these species by short leaves, 3-12 cm long, the sparsely and spirally-arranged, flabelliform and palmately-parted emergences, the presence of a distinct and thin rachis between emergences and the pattern of segments arranged on the male bracts with acute apex.

Type.

Madagascar. Fianarantsoa Province: Amoron’i Mania Region, Manandriana District, elev. 1400 m, 20°14'S, 47°06'E, 20 September 2017, Sino-Africa Joint Investigation Team (SAJIT)-003462 (holotype, HIB!, isotypes, HIB!, TAN!)

Description.

A hydrophyte herb. Rhizomes discoid, 3-8 mm in diameter; 7-12 leaves emerging from the rhizome. Leaves simple, 3-12 cm long, the upper part slightly curved when rising from water, the base enlarged with stipule; stipule ovate-elliptical, basal half dorsally attached on petiole, apex sometimes with a tail ca. 1.5 mm; centre bud enclosed by stipules of inner leaves; emergences spirally arranged on rachis and stretching out into loose layers, denser towards the apex of the leaf and gradually reduced to the base. Rachis obvious, 1-2 mm in diameter, white to light green. Petioles indistinct. Emergences (modified leaf blade lobes) 1-6 mm long, flabellate, basal ones reduced into scale-like, upper ones palmately parted, lobes cuneiform, secondly divided into rectangular to linear terminal lobes; the flat of emergences almost perpendicular to the axis; the apex of emergence slightly rolling up, ciliate at the end, cilia gathering into tufts after rising from water; emergences green to mauve at the pinnacle, the rest dark green. Male spikes 5.4-8.0 cm long, peduncles 4.7-6.2 cm long, covered with few small scale-like emergences. Bracts 1-2.2 mm × 1-2.2 mm, rhombic, dark green; segment I (the terminal segment) acute, flanked by 1-2 tiny lobules on each side; segments II (lobules at the dorsal side of bract) acute or obtuse, 2 rows, each row with 3-5 separated lobules, lobules ca. 0.3 mm high. Stamen sessile, anther oblate, with two divergent thecae dehiscing longitudinally. Female spike not found.

Etymology.

The epithet refers to the flabellate shape of emergences on leaves.

Distribution and ecology.

Only one population was found on rocks in a stream in Manandriana, Madagascar (20°14'S, 47°06'E), at an elevation of 1400 m (Fig. 3 ).

Conservation status.

Hydrostachys flabellifera is currently only known from one location with a very small population. Additionally, all species of Hydrostachys are highly dependent on the moving aquatic environment which is threatened by water pollution, natural system modifications, energy production and mining, all of which could drive the taxon to Critically Endangered (CR) or Extinct (EX) in a very short time ( IUCN 2020). Following Guidelines for IUCN Red List Categories and Criteria (2020), H. flabellifera should be categorised as Vulnerable (VU D2).

Phylogenetic analysis.

Hydrostachys flabellifera was placed in a robust clade together with H. stolonifera and H. imbricata (Fig. 4 ) with a high bootstrap support (BS = 96%), while they share limited morphological characteristics. H. multifida , considered as a clade in morphology, is not a monophyletic group, although with low bootstrap support.

Figures

Figure 1. Hydrostachys flabellifera G. W. Hu, Zhun Xu & Q. F. Wang. A habit B lateral view of stipule and petiole base C ventral view of stipule and petiole base D, E part of the leaf F downside of a leaf emergence G upperside of a leaf emergence H dorsal view of male bract I ventral view of male bract J, K stamen. Drawn by Jing Tian.

Figure 2. Hydrostachys flabellifera G. W. Hu, Zhun Xu & Q. F. Wang A habit B emergences on rachis, cross-section C, D emergences E dorsal view of male bract F ventral view of male bract G top view of stamen.

Figure 3. Distribution of Hydrostachys flabellifera G. W. Hu, Zhun Xu & Q. F. Wang.

Figure 4. Maximum Likelihood tree, based on ITS. Bootstrap values are labelled alongside each node.