Disporum mishmiensis Hareesh & M.Sabu, 2018

Disporum mishmiensis Hareesh & M.Sabu View in CoL , sp. nov. — Fig. 1 View Fig ; Map 1

Disporum mishmiensis is similar to D. leucanthum but differs from it in having a campanulate perigone with pink tepals that are 2.7–3 cm (vs 1.2–2 cm), filaments 14–16 mm long (vs 8–15 mm), a style 16–18 mm long (vs 6–12 mm),and a non-stoloniferous/rhizomatous growth habit. — Type: M. Sabu & V. S. Hareesh 149366 (holo CALI; iso CAL, CALI), India, Arunachal Pradesh, Lohit District , near Tohangam view point,on the way to Hayuliang from Tezu , N27°55'10.94" E96°20'14.014" [ 27.919647, 96.337156], 16 May 2017 GoogleMaps .

Etymology. The name mishmiensis denotes the type locality,Mishmi Hills which is a part of the eastern hills of Arunachal Pradesh adjacent to Myanmar.

Bisexual perennial herb, evergreen. Rhizome short, internodes < 0.5 cm, essentially caespitose, clump-forming. Cataphylls 1 or 2, papery, brownish pink, sheathing the lower stem. Stem occasionally simple or 2- or 3-branched distally, 50–150 cm high, glabrous. Petiole 0.5–1.2 cm long; leaf blade ovate to elliptic or elliptic lanceolate, 5–16 by 1.5–5 cm, acute to acuminate at the apex, cuneate at the base, glabrous, 5–7-nerved. Inflorescences terminal, 5–7-flowered; flowers 2.5–3 cm long, campanulate, pedicels 2.6–2.8 cm long, not ridged, glabrous, pale green. Flowers narrowly campanulate, opening to 1.5 cm wide, tepals pale pink, oblanceolate, 2.7–3 by 0.7–0.8 cm, acute at the apex, narrowed in the lower part, navicular-scaphoid, 1 mm long, minutely papillate on the lower margin and abaxially, only slightly saccate at the base. Stamens distinctly shorter than the tepals, 16–20 mm long; filaments 14–16 mm long, dilated proximally and about twice the diameter as the distal portion, minutely papillate proximally; anthers 5–6 mm long. Ovary obovoid, 5–5.5 by c. 3 mm long. Style slightly shorter than tepals, 16–18 mm long, trifid at the apex.

Phenology — Flowering: May to June; fruiting: June to October.

Habitat & Ecology — Disporum mishmiensis is known only from Tohangam, Lohit district of Arunachal Pradesh (Map 1). The area is characterized by subtropical evergreen forest at moderate elevations (1 000–1 500 m). The new species grows along the open waysides in association with Didymocarpus moellerii A.Joe, Hareesh & M.Sabu ( Gesneriaceae ), Elatostema sp. ( Urticaceae ), Impatiens arguta Hook.f. & Thomson and I. citrina Hook.f. ( Balsaminaceae ), Ophiorrhiza sp. ( Rubiaceae ), etc.

Conservation assessment — Due to the known limited area of occurrence of D. mishmiensis which is less than 1–2 km 2 based on a grid centred on the known population, the species would fall under the category Threatened based on IUCN (2017) criteria, but due to its recent discovery and limited field exploration we prefer to tentatively classify D. mishmiensis as Data Deficient (DD) until further field studies can be performed. The major threat we observed is construction work for the Trans- Arunachal and Frontier Highway projects and shifting cultivation practices may lead to the decrease of the population in future.

Notes — Disporum mishmiensis is a distinctive new species from an underexplored, but diverse region of north-eastern India. This species differs from its most similar congener, D. leucanthum , in multiple characters ( Table 1). Disporum mishmiensis is a larger, typically branched caespitose plant with terminal inflorescences of 5–7 pink flowers.AF has observed in D. leucanthum in the East Siang District of Arunachal Pradesh that it has an unbranched stem with 1 or 2 terminal white flowers in large rhizomatous colonies ( Fig. 2 View Fig ). Furthermore, the two species differ in their habitat preference and elevation; D. mishmiensis occurs below 1 800 m in subtropical forest whereas D. leucanthum prefers 1 900–2 100 m in subtemperate oak forest.

In addition, D. mishmiensis differs from D. cantoniense in its evergreen stems (vs deciduous), terminal inflorescences (vs pseudoaxillary), smooth peduncle and pedicels (vs scabrous) and purple pink flowers (vs purple). Disporum cantoniense var. sikkimense Hara is distinguished by its large perianth that is greenish white ( Hara 1984). In comparison to D. mishmiensis it has scabrous-papillose tepal margins, shorter staminal filaments, smaller anthers, a longer style and it occurs further west where it is documented only from Sikkim ( Hara 1984). Hara (1984) had compared D. cantoniense var. sikkimense to D. megalanthum F.T.Wang & Tang , but the latter species differs from the former and from D. mishmiensis in its axillary inflorescences borne in the proximal part of the stem, typically at the leaf below the first branch, has larger stamens that are 20–28 mm long (vs 16–20), and is also rhizomatous (vs caespitose). Moreover, the closest populations of D. megalanthum occur approximately 300 km east of the only known locality of D. mishmiensis . The presumed closest relative of D. mishmiensis is the sympatric D. leucanthum from which D. mishmiensis differs in numerous characters discussed above and present below ( Table 1). The key below serves to distinguish D. mishmiensis from other Indian species of Disporum .

The systematics of Disporum in India is in need of revision and it is clear from morphological and field observations that several species occur in north-eastern India rather than only D. cantoniense ( Dasgupta 2006) . AF has observed D. cantoniense in China and it is a deciduous species whereas most Indian plants observed are evergreen in habit. For taxonomy of Indian Disporum we recommend Hara (1984, 1988) until a synthetic systematic revision using molecular, cytological, and morphological data has been performed. A key to the species for India and adjacent regions of the Himalaya is provided.

Map 1 Collection locality of Disporum mishmiensis Hareesh & M.Sabu (✶) in India. Inset showing the north-eastern part of India and adjacent countries. The larger map shows the single occurrence of D. mishmiensis in eastern Arunachal Pradesh. The border of Arunachal Pradesh and China and other India states is outlined in red.