Mouretia oblanceolata L.Wu, K.S.Nguyen, B.H.Quang & T.P.Anh, 2021

Anh, Tran Thi Phuong, Nguyen, Khang Sinh, Binh, Tran Duc, Quang, Bui Hong & Wu, Lei, 2021, Mouretia oblanceolata (Rubiaceae), a new species from central Vietnam, Phytotaxa 484 (2), pp. 237-243 : 238-241

Mouretia oblanceolata L.Wu, K.S.Nguyen, B.H.Quang & T.P.Anh , sp. nov. ( Fig. 1 , 2 )

Diagnosis: —Most similar to Mouretia tonkinensis and M. vietnamensis in leaf shape, well-developed stipules and puberulent indumentum of young stems, adaxial corolla lobes and disk, but differing clearly from them by the following traits: erect to sub-erect (vs. procumbent) habit, abaxially glabrous (vs. hairy) stipules, 12–16 (vs. 4–10) pairs of lateral veins, umbrella-like (vs. head-like) cymose inflorescences, deltoid (vs. ovate to obovate or triangular) calyx lobes, longer calyx tube (2.2–2.5 mm long vs. 0.3–0.5 mm long), and revolute, deltoid to ovate (vs. incurved to recurved, triangular) corolla lobes.

Type: — VIETNAM. Ha Tinh province, Huong Son district Kim Son One commune, about 10 km east-northeast direction of Cau Treo international border gate, at elevation of 206 m a.s.l., around point 18.41553°N 105.20136°E, 27 March 2019, B. H . Quang 206 (holotype HN0000074728 !; isotypes CSFI!, HN0000074729 !, HN0000074730 !, HN0000074731 ) .

Paratypes: — VIETNAM. Ha Tinh province, Huong Son district, Kim Son One commune, at elevation of 220 m a.s.l., around point 18.41625°N 105.20170°E, 27 March, 2019; T. D. Binh 78 ( HN0000074732 !, HN0000074733 !, HN0000074734 !, HN0000074735 !, HN00000747436 !) .

Description: —Perennial herb, erect to suberect, terrestrial or epilithic, 10–20 cm tall. Stem unbranched, terete, puberulent when young, later glabrescent, pale green, 3–5 mm in diameter, with internodes of 1–2 cm long. Leaves in equal pairs, opposite, dark green adaxially and pale greenish abaxially, petiolate; petiole 2–4 cm long, sparsely puberulent; leaf blade glabrous on both surfaces, coriaceous, elliptic to oblanceolate, 10.5–18.2 cm long, 3.2–4.5 cm wide, decurrent at base, apex acute to subacute; midrib flat or canaliculate adaxially and strongly prominent abaxially; lateral nerves 12–16 pairs, alternate to sub-opposite, slender, nearly flat and glabrous adaxially, prominent and puberulent abaxially. Stipules interpetiolar, persistent, often reflexed, obcordate, 8–10 mm long, 9–11 mm wide, glabrous, green, with undulate margins. Inflorescences congested-cymose, terminal, erect, 10–30-flowered; peduncle 2–5.5 cm long, densely puberulent; basal bracts 2, lanceolate, 1–2 mm long, 0.5–1 mm wide, puberulent, acuminate at apex, pale green abaxially. Bracteoles (subtending the pedicels) subulate, 0.5–1 mm long, sparsely puberulent. Flowers heterodistylous. Pedicels 2–3 mm long, greenish white, puberulent. Calyx campanulate, greenish white, with pale green apices; tube 2.2–2.5 mm long, 2.4–2.8 mm wide, puberulent abaxially; calyx lobes 5, deltoid, 1–1.3 mm long, 0.3 – 1 mm wide, apex acute and somewhat deflexed, glabrous adaxially and puberulent abaxially. Corolla tube cylindrical, slightly contracted toward the throat, white, 4–5 mm long, 2–2.4 mm wide, glabrous inside, densely puberulent outside; corolla lobes horizontal when open, soon later revolute, deltoid to ovate, 2.5–3 mm long, 2–2.5 mm wide, glabrous adaxially and puberulent abaxially, apex acute to subacute. Stamens inserted above the middle of corolla tube, enclosed by a pilose ring of hairs, 1.3–1.5 mm long; filaments white, glabrous, 0.2–0.3 mm long; anthers dorsifixed, 2-loculed, narrowly oblong, 1.1–1.3 mm long, 0.3–0.4 mm wide, pinkish white or cream white. Ovary 2- loculed, 1.4–1.8 mm long, 1.3–1.5 mm wide; disk concave or funnel-form, puberulent; style filiform, white, glabrous, 4.5–5 mm long; stigma 2-lobed, capitate, 0.8–1 mm long, 1.3–1.5 mm wide, white, densely papillate, lobes exserted from corolla throat. Short-style flowers, fruits and seeds unknown.

TABLE 1. Comparison of diagnostic characters between Mouretia oblanceolata with M. tonkinensis , M. vietnamensis , M.

inaequalis and M. larsenii . The characters of previously described species are taken from Pitard (1922), Tange (1997), and

Chen et al. (2011).

Etymology: ―Species name refers to the oblanceolate shape of the leaf blade.

Vernacular name: —Vietnamese: Mu rê mác ngƯỢc.

Habitat, phenology and conservation status: — Mouretia oblanceolata is only known from its type locality, Ha Tinh province, central Vietnam, at elevations of 206 m a.s.l. The species is found in the understory of primary tropical evergreen forests, near streams in wet places, usually accompanied by Impatiens sp. , Piper sp. , Melastoma sp. , Musa sp. , Tacca sp. , Stephania sp. , Sporoxeia sp. , and some fern species. It is not common in the studied areas, and flowers in March–April. According to the Guidelines for Using the IUCN Red List Categories and Criteria, version 14 ( IUCN 2019), the conservation status of this new species is proposed as “Data Deficient” (DD).

Distribution: —Central Vietnam (Ha Tinh province, Huong Son district), possibly endemic to central Vietnam.

Similar species:— Mouretia oblanceolata is morphologically most similar to M. tonkinensis in leaf shape, rounded to reniform stipules, terminal cymes, puberulent indumentum of peduncles, pedicels, calyx, abaxial corolla tubes and lobes, but remarkably differs by its erect to sub-erect (vs. procumbent) habit, glabrous (vs. sparsely hairy) adaxial leaf surfaces, larger leaves (10.5–18.2 × 3.2–4.5 cm vs. 3–8 × 1–3 cm), greater number of lateral veins (12–16 pairs vs. 4–6 pairs), glabrous (vs. hairy) abaxial stipules, calyx lobes without (vs. with) the apical extension of 1–1.5 mm wilting, deltoid to ovate (vs. triangular) corolla lobes, much larger corolla lobes (2.5–3 × 2–2.5 mm vs. ca. 1.1 × 1 mm), and revolute (vs. incurved to oblique) corolla lobes. The new species is distinct from M. vietnamensis in having obcordate (vs. oblong to obovate) stipules, terminal (vs. axillary, paired at nodes) and umbrella-like (vs. head-like) cymose inflorescences and longer peduncles (2–5.5 cm long vs. 0.5–1 cm long). It can be distinguished from M. inaequalis by its isophyllous (vs. anisophyllous) leaves, 12–16 (vs. 5–8) pairs of lateral veins, and longer peduncles (2–5.5 cm long vs. 0.2–0.5 cm long). In addition, the Mouretia larsenii is quite different from M. oblanceolata by its structure and development of inflorescence, which is a terminal cyme, at first appearing as head-like, later developing two to several arms radiating star-like to 5 cm long, and each arm with 4 rows, similar to a starfish. To help quickly identify and recognize Mouretia oblanceolata , a key and a morphological comparison (Table 1) of all currently known species in the genus are provided below.

Figures

FIGURE 1. Mouretia oblanceolata. A. Habit; B. Stem; C. Leaf, adaxial view; D. Leaf, abaxial view.All photos by Bui H.Q & Tran D.B. from B.H. Quang 206.

FIGURE 2. Mouretia oblanceolata.A. Node showing stipules; B. Stipules, adaxial view; C. Stipules, abaxial view; D & E. Inflorescence, lateral view; F. Inflorescence, apical view; G. Calyx, pedicel and bracteole; H. Long-styled (pin) flower, lateral view; I. Flower apical view; J. Longitudinal section of pin flower; K. Pin flower with corolla partly removed, showing ovary, style and stigma. All photos by Bui H.Q. & Tran D.B. A–G from B.H. Quang 206; H–K from T.D. Binh 78.