We describe Hedychium ziroense sp. nov. from Northeast India (NE India) which was discovered during one of our recent botanical explorations in Arunachal Pradesh. We provide detailed morphological comparison of this species with four other Hedychium species (H. griersonianum R.M.Sm., H. ellipticum Buch.-Ham. ex Sm., H. gomezianum Wall. and H. yunnanense Gagnep.), with which it shares some morphological similarities. The new species is characterised by a dense cylindrical spike, pubescent rachis, folded bracts, 2–3 flowers per cincinnus, deeply cleft labellum and a distinctive late monsoonal flowering phenology from August to September.

Apatani, Arunachal Pradesh, Hedychium , taxonomy, Ziro

The genus Hedychium, comprising more than 80 species (Sanoj 2011), is distributed in the tropical, subtropical and warm-temperate Asia (Indian subcontinent, China and Southeast Asia) and Madagascar (Sirirugsa 1991, Newman et al. 2004, Newman and Pullan 2007, Tanaka et al. 2016, Ding et al. 2018, WCSP 2018). Based on inflorescence type and bract structure, Wallich (1853) recognised four subgeneric divisions within Hedychium: Coronariae (spikes with more or less tightly imbricate bracts), Spicatae (spikes with distant, spreading bracts), Siphonium (characterised by stemless habit and crested anther) and Brachychilum (characterised by an exceedingly small labellum). Based on the relative lengths of stamen and labellum, Horaninow (1862) divided the genus into three groups: Gandasulium (species with shorter stamen compared to labellum), Macrostemium (species with stamen length equal to or exceeding the labellum length) and Brachychilum. Later, Baker (1892) treated Gandasulium (to be corrected as Hedychium, as it includes the type of the genus, M. Newman pers. com.) and Macrostemium as two different sections within the genus Hedychium. Finally, based on the shape of the inflorescence and concealment of the inflorescence rachis, Schumann (1904) divided Hedychium into two subgenera: Gandasulium (to be corrected as Hedychium, mentioned above; characterised by wide, ellipsoid or ovoid inflorescence, dense imbricate bracts and hidden rachis) and Eosmianthus (characterised by longer than wide inflorescence, spreading bracts and exposed rachis). However, the molecular phylogeny of Hedychium by Wood et al. (2000) revealed that the morphologies referred to by Wallich (1853), Horaninow (1862), Baker (1892) and Schumann (1904) were not synapomorphic with any of the subgeneric groups and therefore the subgeneric groups were not supported. Instead, four distinct clades were now identified in the phylogenetic tree based on their biogeographic pattern; clade 1 - mostly Peninsular Malaysian taxa, clade 2 - Chinese and high elevation Himalayan taxa, clade 3 – Hedychium acuminatum and clade 4 - mostly Indian and Burmese (Myanmar) taxa. Interestingly, the number of flowers per cincinnus was the only morphological character that correlated with the clades wherein clade 2 was represented only by the species with 1-flowered cincinnus.

In India, Hedychium is the most diverse genus in the family Zingiberaceae and it is represented by at least 44 taxa (31 species and 13 varieties) from NE India and the Western Ghats (Sanoj 2011). Taxonomic revisions and explorations in the last few decades have resulted in the discovery of several new Hedychium (species as well as varieties) from the NE India and the Western Ghats (Sanoj et al. 2010, Sanoj and Sabu 2011, Thomas et al. 2015, Odyuo and Roy 2017). However, the total species count of Hedychium in India remains ambiguous due to the lack of detailed taxonomic studies, incomplete geographical sampling caused by difficult terrain and political disturbances (Srivastava 1984, Sarangthem et al. 2013, Sarangthem 2015, Ashokan and Gowda 2017). Northeast India consists of eight states, out of which Arunachal Pradesh (previously known as NEFA or North-East Frontier Agency) holds a major share of the Eastern Himalayan biodiversity hotspot (Mani 1974, Paul et al. 2005). It is second highest (20 species) in Hedychium diversity in India, next to Meghalaya (28 species, pers. obs.). Three Hedychium species (H. radiatum, H. raoii and H. robustum) are known to be narrow endemics to Arunachal Pradesh and they are known only from their respective type localities (Rao and Hajra 1974, Pal and Giri 1998, Sanoj 2011).

Here we describe a new species of Hedychium, characterised by more than 1-flowered cincinnus in each bract, from Arunachal Pradesh. The new species shares some morphological features with H. griersonianum R.M.Sm., H. ellipticum Buch.-Ham. ex Sm., H. gomezianum Wall. and H. yunnanense Gagnep. H. griersonianum is known so far from only its type locality in Bhutan (Fig. 1, Table 1). H. ellipticum is one of the widely distributed species with a large variation in its morphology. H. gomezianum is distributed in Myanmar, NE India and Thailand. H. yunnanense is native to Southwest China and Vietnam. All the aforementioned species are characterised by 1-flowered cincinnus in each bract (scarcely two flowers appearing per bract even though the whole inflorescence never completely deviates from the 1-flowered cincinnus structure).

Figure 1. 

Distribution of Hedychium ellipticum, H. gomezianum, H. griersonianum, H. yunnanense and H. ziroense sp. nov. in the Indian subcontinent, China and Southeast Asia.

Field collection trips were planned and conducted in August and September 2017 in selected regions within the state of Arunachal Pradesh. Metadata collection included scoring of morphological, phenological as well as ecological characters. Morphological measurements were taken using both ruler and digital calipers. Collections included herbarium and spirit samples and leaf tissues in silica for further molecular studies.

All Hedychium protologues were examined including monographs and revisions; Koenig 1783, Smith 1811, Roscoe 1828, Wallich 1853, Horaninow 1862, Baker 1892, Schumann 1904, Naik and Panigrahi 1961, Rao and Verma 1969, Srivastava 1984, Smith 1991, Sirirugsa and Larsen 1995, Wu and Larsen 2000, Sanoj 2011, Wongsuwan and Picheansoonthon 2011, Thomas 2015). Herbarium collections, including type specimens, were consulted at ARUN, ASSAM, BHPL, BO, BSA, BSHC, BSI, CAL, MH, QBG, SING, TBGT and in online databases (Global Plants: https://plants.jstor.org/; Kew Herbarium Catalogue: http://apps.kew.org/herbcat/; Muséum national d’Histoire naturelle: https://science.mnhn.fr/; Smithsonian Institution: https://www.si.edu/; The Linnean Collections: http://linnean-online.org/; Zingiberaceae Resource Centre: http://padme.rbge.org.uk/ZRC/; see Appendix 1).

The conservation status for the new species was evaluated according to the International Union for Conservation of Nature (IUCN) guidelines (2017).

The authors thank the Ministry of Human Resource Development (MHRD) and the National Geographic Society for research funds to V. Gowda; IISER Bhopal for the infrastructure; the Council for Scientific and Industrial Research (CSIR) for the senior research fellowship to A. Ashokan and the Heliconia Society International (HSI) for field research grant to A. Ashokan. We also thank the State Forest Department of Arunachal Pradesh for the research permit; ARUN, ASSAM, BO, BSA, BSHC, BSI, CAL, MH, QBG, SING and TBGT for herbarium consultation; and RBGE (E) and Dr. W. John Kress, NMNH (US) for permitting us to use the images. We also thank Dr. Kanchi N. Gandhi for nomenclatural help; Dr. Mark F. Newman and Dr. Piyakaset Suksathan for their critical comments that have helped us improve this manuscript.

List of specimens examined for Hedychium ziroense sp. nov., H. griersonianum, H. ellipticum, H. gomezianum and H. yunnanense. Specimens from the Royal Botanic Garden Edinburgh (E), Royal Botanic Gardens, Kew (K), Linnean Society of London (LINN) and Muséum national d’Histoire naturelle (P) refer to high-resolution digital images of specimens that were examined in this study.