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Begonia dalaiensis B. Das, J. Saikia & D. Banik sp. nov. (Fig. 1, 2) Type: — INDIA. Arunachal Pradesh, Anjaw District, towards Chaglagam, near Meepani bridge, 28°15’53.6’’N, 96°34’28.95’’E, elevation 1335 m, 25 March 2022, Bikas Das, Jadumoni Saikia & Dipanwita Banik CSIR-NEIST 0205, (Holotype: CAL, Isotype: ASSAM, CSIR-NEIST) Diagnosis: —The species in its vegetative form shows greatest similarities with the widely distributed B. acetosella, B. longifolia and B. roxburghii due to its erect nature, caulescent habit and baccate ovary. The new species differs from B. acetosella based on male inflorescence with 12–16 flowers, 3-locular ovary and 2 styles (vs. 3–5 flowers in male inflorescence, 4-locular ovary with 4 styles); from B. longifolia in having a dioecious sexual system and 2 styles (vs. monoecious sexual system and 3 styles); and from B. roxburghii in having a 3-locular ovary with 3-horns, possessing 2 styles (vs. 4-locular ovary with 4 horn like projections bearing 4 styles). Dioecious, caulescent erect herb, perennial, up to 80 cm tall. Rhizome 5–8 cm. Stem branched, erect, slender, green with red tint and white spots, ridged, glabrous, internodes 5–20 cm long, 3–6 cm thick at node. Stipules thick, triangularovate, apex acuminate, glabrous, 1–1.5 × ca. 0.5 cm. Petiole green, ridged like the stem, glabrous, 4.5–9.5 cm long. Leaf blade ovate-lanceolate, 10–18 × 6–10 cm, asymmetric, venation palmate, basifixed, base slightly overlapping to non-overlapping, cordate-oblique, apex acute-acuminate, margin entire, green above, pale green underneath, glabrous on both surfaces. Inflorescence cymose, axillary, peduncle highly reduced, 12– 16 male flowers and 3– 9 female flowers per inflorescence. Bracts greenish-brown, lanceolate-linear, glabrous, nerved, apex acuminate, base truncate, 10–11 × ca. 7 mm, caducous. Staminate flower pedicel glabrous, white to pale pink, 18–25 mm long; corolla ca. 3 cm across, tepals 4 (2+2), white to pink, glabrous, fleshy; outer tepals 2, ovate-elliptic, concave, white-pinkish white, veins somewhat distinct, margin entire, apex rounded-cordate or somewhat erose, 1.4–1.5 × 1.2–1.3 cm; inner tepals 2, glabrous, white to pink, elliptic, margin entire, apex rounded, ca. 1.4 × 1 cm; androecium cylindrical, ca. 10 × 11 mm, stamens 60–90, 5–6 mm long; anther oblong, yellow, 2–2.5 mm, connective extended at apex, apex acuminate, dehisces through lateral longitudinal slits. Pistillate flower pedicel glabrous, 18–22 mm, white-pink, corolla fleshy, 2.8–3 × 2–2.5 cm across; tepals 5, white, unequal, 1–1.7 × 0.6–0.8 cm, oblong to obovate, glabrous, shiny, veins distinct, margin entire, apex rounded, erose; styles 2, free, yellow-white, 0.5–0.8 cm, stigmatic surface twisted; ovary baccate, tri-locular, glabrous, green, tri-horned, placentation axile, placentae bifid, ca. 13 × 7 mm. Fruits not seen. Etymology:— The specific epithet is named after the type locality “Dalai Valley” of Anjaw district, known for its great floristic wealth. Distribution and ecology:— The species shares its habitat with Impatiens sp., Elatostema sp., Melastoma sp., Polygonum sp. and some ferns. It grows along moist shady mountain slopes near streams as well as in forest understory and roadside (Fig. 2). Phenology:— Flowering during March-April. Specimens examined: INDIA. Arunachal Pradesh: Anjaw district, near Meepani bridge, 1335 m, 24 March 2022, B. Das, J. Saikia, D. Banik (CSIR-NEIST 0215) fls.; Lohit district, Hayuliang road, 27°56’00.7”N, 96°21’18.7”E, 1680 m, 06 August 2022, B. Das, J. Saikia, D. Banik (CSIR-NEIST 0210). Conservation status:— Begonia dalaiensis is currently known from two districts of Arunachal Pradesh. Four populations were discovered comprising a total of less than 200 individuals. Based on GeoCAT analysis (Bachman et al., 2011), the species has an extent of occurrence of 38 sq. km area and area of occupancy of 16 sq. km. However the populations are in an almost linear configuration in the montane forest area which greatly reduces the EOO. In addition there is a chance that additional populations could occur in the nearby areas with similar habitats. The data from our initial field survey needs adding to before we are confident in assigning a threat category to B. dalaiensis. Hence, according to the IUCN Standards and Petitions Committee (2022), we provisionally assign B. dalaiensis to the Data Deficient category (DD). Notes:— Begonia dalaiensis belongs to B. sect. Platycentrum based on having a rhizomatous habit, extended anther connectives, 3-locular ovary and convolute stigma; the sectional placement is supported by the molecular phylogeny. The species shows close affinities with the Himalayan species of the former section Sphenanthera, which are mostly comprised of dioecious Begonia with baccate fruits. B. giganticaulis is another dioecious species reported from southern Xizang, China, which shows close affinities with the new species, but differs in attaining a height up to 4 m and in having shortly crested ovary and flowering during June-October whereas B. dalaiensis from Arunachal Pradesh, India grows to approximately 80 cm, has a horned ovary, and flowers in March-April. The differences among these taxa are summarised in Table 2. Phylogenetic position:— The final dataset comprised 408 bases including gaps, with 263 conserved, 66 variable and 79 parsimony informative sites, respectively. The phylogram obtained from Maximum parsimony analysis and Bayesian analysis showed identical tree topology (Fig. 3). The three accessions of the new species formed a clade (BI = 1.00, BS = 96.54%), sister to a clade of the morphologically similar dioecious taxa B. giganticaulis, B. acetosella var. acetosella and B. acetosella var. hirtifolia Irmsch. All species sampled resolved as monophyletic., Published as part of Das, Bikas, Saikia, Jadumoni, Konwar, Parthapratim, Siga, Appu & Banik, Dipanwita, 2022, A new dioecious species of Begonia (Begoniaceae) from Arunachal Pradesh, India, pp. 89-96 in Phytotaxa 575 (1) on pages 91-94, DOI: 10.11646/phytotaxa.575.1.6, http://zenodo.org/record/7403333, {"references":["Bachman, S., Moat, J., Hill, A. W., de Torre, J. & Scott, B. (2011) Supporting Red List threat assessments with GeoCAT: geospatial conservation assessment tool. ZooKeys 126: 117 - 126. https: // doi. org / 10.3897 / zookeys. 150.2109","IUCN Standards and Petitions Committee. (2022) Guidelines for Using the IUCN Red List Categories and Criteria. Version 15.1. Prepared by the Standards and Petitions Committee. [https: // www. iucnredlist. org / documents / RedListGuidelines. pdf]"]}