Hydrostachys flabellifera (Hydrostachyaceae), a new species from Madagascar Zhun Xu 1,2,3 , Jing Tian 1,2 , Solo Hery Jean Victor Rapanarivo 4 , Rokiman Letsara 4 , Rivontsoa A. Rakotonasolo 3,4,5 , Guy E. Onjalalaina 1,2,3 , Guang-Wan Hu 1,2 , Qing-Feng Wang 1,2 1 Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China 2 Sino-Africa Joint Research Center, Chinese Academy of Sciences, Wuhan 430074, China 3 University of Chinese Academy of Sciences, Beijing 100049, China 4 Dé- partement Flore, Parc Botanique et Zoologique de Tsimbazaza, Antananarivo 101, Madagascar 5 Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China Corresponding authors: Guang-Wan Hu (guangwanhu@wbgcas.cn); Qing-Feng Wang (qfwang@wbgcas.cn) Academic editor: Y. Mutafchiev | Received 10 September 2020 | Accepted 6 November 2020 | Published 20 November 2020 Citation: Xu Z, Tian J, Rapanarivo SHJV, Letsara R, Rakotonasolo RA, Onjalalaina GE, Hu G-W, Wang Q-F (2020) Hydrostachys fabellifera (Hydrostachyaceae), a new species from Madagascar. PhytoKeys 167: 45–56. https://doi. org/10.3897/phytokeys.167.58538 Abstract Hydrostachys fabellifera, a new species of Hydrostachyaceae found in a stream in Manandriana, Madagas- car, is described and illustrated herein. It is similar to H. verruculosa and H. laciniata in morphology, but can be distinguished from them by its leaves with sparsely arranged, fabelliform and palmately parted emergences, obvious rachis and the pattern of segments arranged on the male bracts. Molecular phyloge- netic analysis of the nuclear ribosomal internal transcribed spacer (ITS) dataset provides a robust support for it as a new species as well. Keywords Aquatic plants, Cornales, endemic, new taxa, taxonomy Copyright Zhun Xu et al.. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. PhytoKeys 167: 45–56 (2020) doi: 10.3897/phytokeys.167.58538 https://phytokeys.pensoft.net reseArCH ArtiCle Launched to accelerate biodiversity research A peer-reviewed open-access journal