Sonerila souvannii Phonep. & Soulad., 2021

Phonepaseuth, Phongphayboun, Souladeth, Phetlasy, Souvannakhoummane, Keooudone, Vongthavone, Thyraphon & Tagane, Shuichiro, 2021, Two new species of Sonerila Roxb. (Melastomataceae) from Laos, European Journal of Taxonomy 755, pp. 136-148 : 141-143

Sonerila souvannii Phonep. & Soulad. sp. nov.

urn:lsid:ipni.org:names:77217799-1

Figs 3–4

Diagnosis

Sonerila souvannii sp. nov. is similar to S. cardamomensis , described from Cambodia, in its acaulescent habit and in the shape of its leaves, but it differs in the shape of its rhizome (cylindrical in S. souvanii vs bulbous in S. cardamomensis ), larger leaves (8–10 × 6–9 cm vs 1–4 × 0.9–2.7 cm), petiole length and color (8–15 cm long and light green vs 0.4–2.5 cm long and reddish brown), greater number of flowers per cyme (20–25 vs 5–11), and petal length and pubescence (9–10 × 6–7 mm and glabrous vs 5.5–6 × 3.5–4 mm with glandular trichomes on midveins abaxially). Sonerila souvannii sp. nov. is also similar to S. dongnathamensis from Thailand in the shape of its inflorescences, but differs in the rhizome shape (cylindrical vs globose), the shape of the leaf base (cordate vs obtuse to rounded), pedicel length (10–25 mm long vs 1–4 mm long), the number of flowers per cyme (20–25 vs 5–12), and in the length and outline of the petals (9–10 × 6–7 mm, acute vs 3–5 × 3–4 mm, acuminate with long seta). The new species is also related to S. tuberosa from Cambodia, but distinguished in the rhizome shape (cylindrical vs slightly bulbous), the shape of the leaf base (cordate vs very broadly ovate to orbicular), pedicel length (10–25 mm long vs 5–6 mm long), the number of flowers per cyme (20–25 vs 4–8), and in the length and outline of the petals (9–10 × 6–7 mm, acute vs 5 × 2.7 mm, elliptic, apiculate, pink) ( Table 2 ).

Material examined

Type LAOS • Vientiane Capital, Naxaythong District, Darn Sinxay temple area; 210 m a.s.l.; 12 Sep. 2020; Phonepaseuth P012 ; holotype: FOF!; isotypes: HNL, KAG .

Etymology

The specific epithet honours Keooudone Souvannakhoummane (Centre for Development and Environment), a plant taxonomist who has greatly contributed to our understanding of plant diversity in Laos through the description of many new species in various families for the flora of Laos.

Vernacular name

ຊີດິນສຸວັນ [ʻSouvan’s Seedinʼ (meaning: ʻSouvan’s Sonerila ʼ)].

Description

Lithophytic perennial herb, 12–15 cm tall. Stem cylindrical, ca 2 cm long, 8–10 mm in diam., with a rhizome at the base, rhizome green when young then turning to brown with age, with rudimentary leaves on buds on the rhizome. Leaves forming a basal rosette; lamina (ordinary leaves) ovate, 8–10 × 6–9 cm, membranous when dried, green, covered with hirsute hairs adaxially, pale green, covered with whitish hirsute hairs mainly along the veins abaxially, apex acute, base cordate, margin finely crenate and long ciliate, midrib sunken abaxially, with 4–5 pairs of lateral primary veins originating from a common point at the base, impressed adaxially, prominent abaxially; petiole 8–15 cm long, light green, densely villous except near base which is glabrous. Rudimentary leaves ovate, 0.2–0.6 cm long, with long spike hairs. Inflorescence terminal, scorpioid cyme, 20–25-flowered, of which 2–3 flowering at a time; peduncle 8–12 cm long, 2–2.5 mm in diam., sparsely covered with villous hairs. Bracts rachis and minute. Hypanthium greenish pink, campanulate, 5–6 mm long, 2–2.5 mm in diam., sparsely covered with villous hairs, Calyx lobes 3, ovate-triangular, ca 1 × 2.5 mm, apex short acuminate; pedicel 1–2.5 cm long, 0.8–1 mm in diam., sparsely covered with glandular trichomes. Petals 3, elliptic, 9–10 × 6–7 mm, pinkish purple adaxially, pale pink tinged with shiny green, with a pinkish purple line along the midrib abaxially. Stamens 3, anthers lanceolate, 5.5–6 mm long, bright yellow, basally inflated and deep cordate, filaments 6–7 mm long, glabrous, white. Ovary 3-locular, elliptical, placentation axillary, style 10–12 mm long, glabrous, white, stigma capitate. Capsule ovoid-ellipsoid, 5–7 × 2.5 mm, smooth outside. Seeds brown, numerous.

Distribution, habitat and phenology

Sonerila souvannii sp. nov. grows in loose soil in the crevices of shaded rocks at 200–210 m a.s.l. It grows in the understorey of lowland semi-evergreen forest together with Begonia martabanica A.DC. ( Begoniaceae C.Agardh ), Phyllagathis tuberosa (C.Hansen) Cellin. & S.S.Renner ( Melastomataceae Juss. ) and Davallia denticulata (Burm. f.) Mett. ex Kuhn ( Davalliaceae M.R.Schomb. ex A.B.Frank ). Flowering and fruiting in September.

Preliminary conservation status

We found three small sub-populations of S. souvannii sp. nov. with each comprising only 5–6 individuals, about 20 m apart. The species has not yet been found anywhere else. Considering the species grows in a very narrowly restricted area where human activity, such as collection of non-timber forest products (NTFPs) and the logging of wood for local uses, can be seen, we need to pay attention to its conservation. As the number of mature individuals is less than 50, we assess this species as Critical Endangered (CR) criteria D ( IUCN 2019).

Figures

Fig. 3. Sonerila souvannii Phonep. & Soulad. sp. nov. A. Habit. B. Front view of flower. C. Petals. D. Hypanthium and style, with portion of pedicel. E. Cross section of ovary. F. Stamens. G. Style and stigma. H. Capsule. I. Rachis and minute bracts. Line drawings from holotype (Phonepaseuth P012) by K. Souvannakhoummane.

Fig. 4. Sonerila souvannii Phonep. & Soulad. sp. nov. A. Habitat (on sandstone rock). B. Habit. C. Petiole densely covered with villous hairs. D. Rhizome and stem with rudimentary leaves. E. Flowers. F. Inflorescence (scorpioid cyme). G. Lateral view of flower. H. Back view of flower. I. Longitudinal section of fruit.J. Top view of fruit. K. Cross section of fruit.L. Infructescence of the last season. Photos by P. Phonepaseuth on 12 September 2020.