Vietnamocasia, a new genus from Central Vietnam belonging to the AlocasiaColocasia clade (Araceae)

1 Department of Bio-resources, Institute of Tropical Biology, Vietnam Academy of Science & Techonlogy, 85 Trần Quốc Toản Road, District 3, Ho Chi Minh City, Vietnam.
2 Department of Plant Science and Environmental Ecology, Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia;
3 Research Associate, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA 02138, United States.
4 Institut de Systématique, Évolution, Biodiversité, ISYEB - UMR 7205 CNRS, Museum national d’histoire naturelle, École Pratique des Hautes Études – Université Pierre et Marie Curie, Sorbonne Universités, CP39, 57 rue Cuvier, 75231 Paris Cedex 05, France.
5 Vietnam Academy of Science & Techonlogy -Institute of Ecology & Biological Resources (IEBR), Hanoi, Vietnam.
6 Honorary Research Scientist, Ludwig–Maximilians–Universität München, Department Biologie I, Systematische Botanik und Mykologie Menzinger Straße 67, 80638 München, Germany.

Vietnamocasia, a new monotypic aroid genus in the Alocasia-Colocasia clade, is described with the type species, Vietnamocasia dauae. Vietnamocasia is distinguished by possessing free individual staminate flowers, lacking expanded synconnectives, and having nodding inflorescences. Vegetatively Vietnamocasia is reminiscent of species of the distantly closely related Alocasia Cuprea Group, although Vietnamocasia is so far only known from the type locality in Central Vietnam, over
1200 km NE from the nearest representative of the Alocasia Cuprea Group. The phylogenetic analyses of Vietnamocasia dauae together with representative taxa from all genera of the Alocasia-Colocasia clade recovered Vietnamocasia as a strongly supported clade sister to Alocasia, together nested in a clade to which Leucocasia is a sister taxon. Vietnamocasia dauae is illustrated from living plants and with a line drawing. A key to all genera of Alocasia-Colocasia clade is included.

Key words: Endemics, Indochina, Malesia, phylogeny, Vietnamocasia dauae

The Araceae is one of the largest families of monocots with an estimated 6000 species (of which about 3500 are formally described) in 128 genera (Mayo et al. 1997, Boyce & Croat 2011). The highest diversity concentrated in the humid tropics of the Neotropics, Afrotropics, and IndoMalaya. Many aroid genera remain taxonomically poorly understood, with fieldwork consistently discovering undescribed taxa.
The Alocasia-Colocasia clade comprises about 110 species diminutive geophytes to massive pachycaularborescent terrestrial or epilithic mesophytes, rather rarely helophytes, distributed from the subtropical eastern Himalayas throughout subtropical and tropical parts of Asia into the western pacific and eastern Australia. The most recent phylogenetic analyses of Araceae (Cusimano et al. 2011, Nauheimer et al. 2012a,b) revealed Colocasieae (sensu Mayo et al. 1997) as a polyphyletic assemblage with Leucocasia gigantea (Blume 1823: 103) Schott (1857:34) forming a well-supported separate clade along with Alocasia (Schott 1832: 18) G.Don in Sweet (1839: 631). Consequently the rank Colocasieae can no longer be used for the Alocasia-Colocasia clade since it lacks phylogenetic support. While Alocasiinae formally exists (Schott, 1856: 43) its rank is inappropriate and in any case its historical usage is incongruent with the retrieved phylogeny. Therefore we opt to use rankless Alocasia-Colocasia clade which includes the Colocasia clade (Cusimano et al. 2011, Nauheimer et al. 2012a,b) with Alocasia and Leucocasia Schott (1857: 34) in the Alocasia clade. The Alocasia-Colocasia clade includes Alocasia, Ariopsis Nimmo in Graham (1839: 252), Colocasia, Englerarum Nauheimer & Boyce (2014: 713, epublished 2013), Leucocasia, Steudnera Koch (1862:
114), Remusatia Schott (1832: 18), and Vietnamocasia from this study.
During a 2010 floristic investigation of Mount Dầu, specifically the Khánh Giang-Trường Lệ community forest in Nghĩa Hành District, Quảng Ngãi Province, Central Vietnam, a small population of a highly unusual colocasioid aroid was encountered sterile by the first and third authors. Subsequently between May and August 2015 five fertile collections were made by the first author. Comparison with herbarium specimens and relevant taxonomic literature revealed these plants to not belong to any described species. In addition, these plants possess separate staminate flowers which comprised of 2–3 stamens (not formed into synandria) and lack an expanded synconnective. Although confident that these plants represented an undescribed species it remained unclear to which, if any, existing genus they should be assigned. To establish the generic position sequences were generated from three chloroplast loci, the trnL-F intergenic spacer, the rpl20-rps12 intergenic spacer, and the trnK/matK region, and one nuclear gene, phytochrome C (phyC), and analysed along with representative sequences of all genera of the Alocasia-Colocasia clade sensu Nauheimer et al. (2012a). The result of these analyses revealed that the plant represented a new genus as well as a new species of the Alocasia-Colocasia clade, here described as Vietnamocasia dauae N.S.Lý, S.Y.Wong, T.Haevermans & D.V.Nguyen.

Materials and methods
Taxonomic study:—Measurements and descriptions were made from mature living plants, herbarium specimens (VNM, P), and spirit material preserved in 70% ethanol. A taxonomic key is constructed based on living materials where possible and combined with Nauheimer & Boyce (2014). Conservation status was assessed using the IUCN Red list Categories and Criteria version 3.1 (IUCN 2012).

 Vietnamocasia dauae
FIGURE 3. Vietnamocasia dauae. A. Habit; B. Leaf blades: adaxially and abaxially with their closed-up of the leaf bases (from left); C. Inflorescence (front view); D. Cataphyll, spathe (back view), and spadix (from left); E. Close-up of pistillate (E1), sterile interstice (E2) and staminate zones showing free individual staminate flowers (a red arrow, E3); F. Closed-up of appendix; G. pistillate zone after anthesis with lower spathe; H. Fruit spathe (back and front views); I. Longitudinal section of fruit spathe and infructescences (from left).

Vietnamocasia daua
FIGURE 4. Vietnamocasia dauae. A. Habit; B. Details of leaf base; C. Apical part of stem showing cataphylls of infructescence and continuation shoot; D. Inflorescence; E. Spadix; F. Ovary (top view); G. Ovary (side view); H. Cross-section of ovary; I. Synandrodes, top view; J. Synandrodes, side view; K. Stamen, side view; L. Stamens, top view; M. Stamens, side view; N. Infructescence.

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