Melastoma calcicolum Souvannakhoummane & Tanaka & Souladeth & Tagane & Dang & Yamamoto & Yamazaki & Pham & Phonepaseuth & Vongthavone & Phengmala & Kongxaisavath & Sengthong 2026, sp. nov.

Melastoma calcicolum Souvann. & Tagane sp. nov. urn:lsid:ipni.org:names:77372121-1 Figs 1, 3 Diagnosis Similar to Melastoma saigonense (Kuntze) Merr., but differs in its terete young twigs (vs. (sub) quadrangular), narrower leaves (ovate-lanceolate to lanceolate, length/width ratio 2.8–4.1 vs. ovate to elliptic, length/width ratio 1.8–2), penicillate emergences spaced apart (vs. densely covered by penicillate emergences), stalk of emergences on hypanthium 1–1.5 mm long (vs. 3–5 mm long), glabrous sepals except for ciliate margins (vs. outer surface densely covered with bristles), and longer styles (20–25 mm long vs. 15–20 mm long). Etymology The specific epithet refers to the limestone habitat. Type material Holotype LAOS • Khammouane Province, Hinboun district, Phou Hin Poun National Protected Area, Khoun Kongleng walking trail; 203 m a.s.l.; 6 Sep. 2024; Tagane et al. Z1704; holotype: FOF [FOF0007160]; isotypes: KAG [KAG188367], VNM. Paratypes LAOS • Khammouane province, Hinboun district, Phou Hin Poun National Protected Area, Khoun Kongleng walking trail; 194 m a.s.l.; 6 Sep. 2024; Tagane et al. Z1693; FOF [FOF0007159] • same data as for preceding; KAG [KAG188355], VNM. Vernacular nameeøນø້ęຂຸນກøງOiǝງ En R Khoun Kongleng (meaning: ʻKhoun Kongleng'sMelastoma'). Description Deciduous shrubs, up to 2.5 m tall. Twigs terete, densely covered with light pale yellow, lanceolate, ascending bristles when young, older twigs grayish to brown, terete, glabrescent to sparsely covered with bristles; internode 0.4–2.4 cm. Leaves opposite, crowded at the top of twigs; lamina ovate-lanceolate to lanceolate, (2–)3.5–8 × (0.5–) 0.9–2.9 cm, length/width ratio 2.8–4.1, base obtuse to rounded, rarely cuneate, margins entire, apex acute to acuminate, acumen up to 1.5 cm long, adaxial surface grayish green, minutely scabrid with conspicuously abundant elongate wavy spicule-like rows of crystalliferous cells which are typically proximal to long hairs, hairs 0.4–1.2 mm long, abaxial surface dull yellowbrown to light yellowish brown, covered with bristles 0.4–1.2 mm long on the midrib and longitudinal nerves, and 0.3–0.5 mm long on the secondary veins; longitudinal nerves running from base to apex 4 in addition to the midrib, impressed adaxially, prominent abaxially; secondary veins subparallel, 0.8–1.5 mm apart, inconspicuous adaxially, slightly prominent abaxially; tertiary veins branching into a conspicuous reticulate network; petioles, slightly concave adaxially, 0.4–1.8 cm long, ca 1 mm in diameter, indumentum as in young twigs. Inflorescences terminal cymes of three (rarely five) flowers, or flowers solitary. Pedicels slender, 5–10 mm, ca 2.5 mm in diameter, with white fine soft strigose hairs. Bracts two, caducous, dull yellow brown with dark-purple margin, ovate to broadly ovate, 4–6 × 2.5–5 mm, densely covered with light yellow, lanceolate, appressed bristles except on the dark-purple marginal portion, apex acute. Hypanthium narrowly funnel-shaped or campanulate, 6–12 × 6–8 mm, densely covered with light pale yellow bristles and dark reddish penicillate emergences, penicillate emergences 0.5–2 mm long, stalk of emergences 1–1.5 mm long, spaced apart between penicillate emergences, crowned by 40–56 bristles; bristles 0.5–1.2 mm long; sepals 5, pink to light green to dark purple, narrowly triangular, 8–10 × 2–2.5 mm, glabrous except for ciliolate margins, apex narrowly attenuate; intersepalar emergences penicillate, 4–5 mm long, crowned by 40–56 bristles; bristles 0.5– 1.2 mm long; hypanthium stalk ca 1 mm long, reddish brown. Petals 5, broadly obovate, 24–30 × 20–26 mm, purple, glabrous on both surfaces except for a few bristles near the apex, apex broadly obtuse. Stamens anisomorphic comprising 5 longer stamens and 5 shorter stamens; longer stamens 35–42 mm long; filaments 17–30 mm long, yellowish; anthers 8–12 mm long, pale purple, connectives 10–15 mm long, strongly incurved, with a yellow basal bifurcate extension, glabrous; shorter stamens 20–22 mm long; filaments 14–18 mm long, yellowish; anther 8–9 mm long, linear-rostrate, pale purple; connective not prolonged, with a yellow basal bifurcate extension, glabrous. Pistil 32–35 mm long; ovary ovoid to ellipsoid, 8–10 × 6–8 mm, greenish, densely covered with bristles at upper part; style filiform, slightly curved apically, 20–25 mm long, glabrous, stigma blunt. Fruits baccate, subglobose to ellipsoid, 9–12 × 7–9 mm, with persistent hypanthium scales as described above. Distribution, habitat and phenology This species is so far known only from the type locality in Phou Hin Poun National Protected Area, Hinboun District, Khammouane Province, central Laos. It grows on an exposed limestone hilltop, where it is associated with Terminalia calamansanai (Blanco) Rolfe (Combretaceae), Phyllanthus mirabilis Müll.Arg. (Phyllanthaceae), Tetrastigma fruticosum Soulad., Phonep. & Tagane (Vitaceae), Falconeria insignis Royle (Euphorbiaceae), Pouzolzia zeylanica var. calcicola Friis & Wilmot-Dear (Urticaceae), Paraboea sp. (Gesneriaceae), Pandanus sp. (Pandanaceae), Dracaena sp. (Asparagaceae), and Aetheolirion stenolobium Forman (Commelinaceae). Flowering is from August to September and fruiting from September to November. The leaves are deciduous from the late dry season in October to the beginning of the rainy season in May. Preliminary conservation status Melastoma calcicolum sp. nov. is known only from the type locality, where we observed one population with about 80 mature individuals. Despite being in a protected area, it is slightly exposed to disturbs caused by ecotourism activities such as the construction of restaurants and walkways. The Area of Occupancy (AOO) is 4 km 2. The Extent of Occurrence (EOO) can be regarded as the area of Phou Hin Poun NPA, 500 km 2, as the same type of exposed limestone karst habitat can be seen widely in the NPA, and the species could be locally abundant. Given this situation, it is preliminarily assessed as Endangered (EN) under the IUCN criteria B2a, b (iii). Notes The penicillate hypanthium emergences are a good character for this species. In Indochina, only M. saigonense and M. orientale have similar hypanthium emergences. However, the new species is easily distinguished from M. saigonense by the characters provided in the diagnosis above, and from M. orientale by its larger flowers. In addition, the habitats of the three species are completely different: M. calcicolum sp. nov. is restricted to exposed limestone rocks, whereas M. saigonense and M. orientale grow on dry or swampy ground, in exposed places with full sun or exposed grasslands (Meyer 2001).