Meiogyne arunachalensis N.V.Page, 2023

Page, Navendu, 2023, A NEW SPECIES OF MEIOGYNE (ANNONACEAE) FROM THE EASTERN HIMALAYAS OF NORTHEAST INDIA, Edinburgh Journal of Botany 80 (1954), pp. 1-8 : 2-7

Meiogyne arunachalensis N.V.Page , sp. nov.

Meiogyne arunachalensis is morphologically similar to M. maxiflora D.M.Johnson & Chalermglin in size, shape and texture of leaves; position of the inflorescence; and shape and texture of monocarps. Meiogyne arunachalensis is a larger tree, reaching up to 30 m in height with girth exceeding 200 cm (vs height up to 20 m and girth up to 125 cm in M. maxiflora), size of the flowers – outer petals up to 6 cm long (vs outer petals up to

3.5 cm long), corrugated patch 1/3 of the inner petal (vs 1/8 of the inner petal), number of carpels 15–18 (vs 4–6), number of seeds 5 in one row (vs 11 in two rows). – Type: India, Arunachal Pradesh, East Siang District, Mebo Taluk , near Sirem (Seram) Village , 28°01′12′′N, 95°27′48′′E, 144 m, 1 viii 2018, N. V. Page 22202 (holotype BSD; isotypes DD, WII). Figures 1 , 2 , 3 .

Tree to 30 m tall, with conical profile, girth at breast height to 200 cm, branches more or less horizontal or slightly sloping with drooping leaves; bark brown with horizontal segments formed due to lenticels. Twigs densely brown fulvous pubescent, gradually becoming glabrous with maturity. Leaves chartaceous, shiny, dark green adaxially and abaxially, drying olive-green, oblong-elliptic, 18–32 × 5.5–8.5 cm, base obtuse, apex acuminate, acumen

1.4 cm long, glabrous adaxially, densely fulvous pubescent with erect brown hair abaxially; midrib channelled and glabrous adaxially, raised and fulvous pubescent abaxially, secondary nerves 19–24 on either side, more or less parallel but curving gradually towards leaf margin, plane and glabrous adaxially, raised and fulvous tomentose abaxially, tertiary venation distinct, raised and sparsely pilose abaxially, percurrent; petiole 0.5–0.7 cm long, fulvous pubescent. Inflorescences ramiflorous from old branches or axils of fallen leaves, 1-flowered; pedicels 0.8–1.2 cm long, densely fulvous hirsute, with one bract on the proximal half of the pedicel. Sepals connate, deltoid, 5–7 × 5–7 mm, densely fulvous pubescent, apex acute, reflexed, margins revolute, brown pubescent abaxially. Petals pale yellow turning pink with age in vivo, lanceolate; outer petals lanceolate, spreading at anthesis, 5–6 × 1.2–1.6 cm

in the middle, apex acute to attenuate, densely silky pubescent with appressed hair up to

2 mm long on adaxial and abaxial surface; inner petal lanceolate, erect or spreading at anthesis, 4–5 × 1–1.3 cm in the middle, apex acute, with a corrugated patch on proximal 1/3 of adaxial surface, densely silky pubescent with appressed hair up to 2 mm long on adaxial and abaxial surface, corrugated patch glabrous. Stamens wedge-shaped c. 2–2.5 mm long, anther connectives flat, glabrous. Carpels 15–18, ovaries c. 2.5 mm long, stigmas ellipsoid, c. 2 mm long, sparsely setose. Torus c. 6–7 mm in diameter. Fruit of 5–12 monocarps borne on pedicels 1.5 cm long. Monocarps sessile, oblong, ovoid or ellipsoid 3–3.5 × 1.5–2 cm, densely covered with short erect brown hair, apex and base rounded. Seeds up to 5 per monocarp, in a single row, oblong (young), mature seeds not seen.

Distribution. This species has so far been recorded in the East Siang district as well as the Changlang district in Namdapha National Park of Arunachal Pradesh. It is likely that it may also occur in the intervening districts of Lower Dibang Valley and Lohit, and also in northern parts of Myanmar in areas neighbouring Namdapha National Park.

Habitat and ecology. Low elevation, wet forests between 140 m and 600 m. Observed growing in the remnant patches of forests in the plains along the banks of the River Brahmaputra. This species also occurs in the foothills of the Eastern Himalayas, on the slopes along stream courses and in the primary wet forests. This species is not common anywhere; its occurrence can be classified as rather uncommon or rare. Flowering from September to November and fruiting from November to April.

Etymology. The specific epithet refers to the state of Arunachal Pradesh, where the species is described from and hitherto geographically restricted to.

Proposed IUCN conservation category. The species is currently known from fewer than five locations. Following IUCN guidelines, the area of occupancy (AOO) is estimated to be 20 km 2. Additionally, continuing decline in the AOO is inferred based on field observations, especially in the plains along the banks of Brahmaputra, where the habitat of this species is declining due to logging and other anthropogenic activities. This species is therefore provisionally assessed as Endangered (B2a,b) until more information on its population and distribution range becomes available.

Notes. The Table summarises the differences between Meiogyne arunachalensis and M. maxiflora.

Additional specimens examined. INDIA. Arunachal Pradesh: East Siang District, Paasighat, on the way to Rengging , 28°05′44.2′′N, 95°16′50.8′′E, 275 m, 5 xi 2020, N. V. Page 22203 ( WII) .

Figures

Figure 1. Habit of Meiogyne arunachalensis N.V.Page, sp. nov. A, Canopy profile; B, bark texture and pattern of branching from the main trunk; C, outer canopy showing the horizontal to gently sloping nature of branches and the drooping nature of leaves. Photographs: Navendu Page.

Figure 2. Vegetative characters of Meiogyne arunachalensis N.V.Page, sp. nov. A, Adaxial surface of leaves; B, abaxial surface of leaves; C, nature of secondary and tertiary veins on the abaxial surface; D, young branch with fulvous pubescent indumentum. Photographs: Navendu Page.

Figure 3. Reproductive characters of Meiogyne arunachalensis N.V.Page, sp. nov. A, Flower at early anthesis; B, flower at late anthesis; C, pedicel, bracts and sepals; D, stamens and carpels surrounded by corrugated patch on the adaxial surface of inner petals; E, fruit with ovoid or ellipsoid monocarps; F, longitudinal section of a young monocarp, showing uniseriate arrangement of seeds. Photographs: Navendu Page.