Ophiorrhiza hoanglienensis T.V.Do, 2020

Nguyen, Thanh Trung, Wei, Yi-Gang, Wen, Fang, Le, Khuong Duy & Do, Truong Van, 2020, Ophiorrhiza hoanglienensis (Rubiaceae), a new species from north-western Vietnam, Phytotaxa 438 (4), pp. 256-262 : 257-261

Ophiorrhiza hoanglienensis T.V.Do , sp. nov. ( Figs. 1 & 2 )

It is morphologically similar to O. napoensis and O. fangdingii but it differs from these two species in having stipules oblong-lanceolate, 9–13 mm long, persistent, leaves in equal or subequal pairs, inflorescences congested-cymose with 5–10-flowered, bracts well-developed, lanceolate, 15–20 mm long, calyx unequally 5-lobed, lobes narrowly lanceolate, longest one 3.2–3.5 mm long, shortest one 1.2–2 mm long, corrolla exclusively white with tube 25–28 mm long, hairy at apical part inside, and lobes ovate to broadly triangular, dorsally ribbed without horn.

Type: — VIETNAM. Lai Chau province: Tam Duong district, Son Binh commune, elev. 1828 m, 27°46’31.87”N, 108°33’0.84”E, on the ridge of Hoang Lien Son mountain range , along 4D national road, ca. 3 km from Tam Duong to Ton forest station, Hoang Lien National Park , 18 October 2017, Do Van Truong et al. VNMN _ CN 895 (Holotype: VNMN!; Isotype: IBK!) .

Perennial herbs, erect or weak at base, to 40 cm long, sometimes branched. Stems terete and glabrous. Leaves often in equal or subequal pairs, ovate-lanceolate, lanceolate or elliptic-oblong, 5–11 × 2–3.2 cm, acuminate to narrowly cuneate at base, acuminate or cuspidate, slightly oblique, ca. 1 cm long at apex, glabrous on both surfaces, adaxially green, abaxially pale green or whitish becoming yellowish when dry, lateral venation pinnate, 13–14 pairs, adaxially shallowly sunken, abaxially prominent, merged at margin. Petioles 3–6 mm long, glabrous. Stipules narrowly oblong-lanceolate, 9–13 × 2–3 mm, entire or cleaved up to ¾ the length, glabrous on both surfaces, margin entire, persistent. Inflorescence terminal, congested-cymose, 5–10-flowered; inflorescence branches helicoid or scorpioid cymes, 5–8 mm long, fine pubescent with congested flowers. Peduncle 8–13 mm long, glabrous. Bracts well-developed, lanceolate, 15–20 × 3–4 mm, venation reticulate and prominent on both surfaces, margin entire. Flowers distylous. Pedicels 1–1.5 mm long, pubescent. Hypanthium subturbinate, 1.3–1.5 × 1.5–1.7 mm, sparsely hairy or glabrescent; calyx lobes unequal, narrowly lanceolate, longest one 3.2–3.5 × 0.3–0.4 mm, shortest one 1.2–2 × 0.25–0.3 mm, membranous, reticulate venation, glabrous. Corolla funnel-form with cylindrical basal part of the tube, exclusively white, drying greenish or yellow, glabrous outside; corolla tube 25–28 × ca. 2 mm, straight or sometimes slightly curved, glabrous inside, except for some sparse hairs at throat; corolla lobes upright, ovate to broadly triangular, 4–5 × 3–4 mm, acute at apex, glabrous on both surfaces, lobes dorsally ribbed and without horn. Longistylous flower: stamens included, inserted at the top part of the corolla tube wall; filaments 1.2–1.5 mm long; anthers linear, 2–2.2 mm long; style situated above anthers, filiform, as long as the length of corolla tube or lightly longer, 27–29 × ca. 0.2 mm, glabrous; stigmas 2-lobed, lobes oval or roundish, 1 × 1.2–1.5 mm, golden, sparsely hairy. Brevistylous flower: stamens inserted at the top part of the corolla tube wall; filaments 1.2–1.4 mm long; anthers oblong linear, 2.3–2.6 mm long; style situated below anthers, filiform, much shorter than the corolla tube, 13–14 mm long, glabrous; stigmas 2-lobed, oval or lanceolate, ca. 2 mm long, glabrous. Capsules not seen.

Etymology: —The specific epithet refers to Hoang Lien, a mountain range of north-western Vietnam from which the new species was collected.

Phenology: —Flowering was observed from October to November. Fruiting time of the new species may start from December or early January.

Distribution and ecology: — Ophiorrhiza hoanglienensis is currently only known from Hoang Lien mountain range, north-western Vietnam, where only two populations were found. The new species grows on the banks of streams in dense evergreen broad-leaved forests or moist and humid sites nearby trails, at elevations of 1800–2100 m, along with the dominant vegetation of Fagaceae ( Quercus spp. ), Lauraceae ( Lindera spp. , Litsea spp. ), Ericaceae (Rhoderodendron spp.), Urticaceae ( Elatostema spp. ), Gesneriaceae ( Henckelia pumila (D. Don) A. Dietr. ).

Conservation status:—Only two small-sized populations of O. hoanglienensis were found in the non-protected and protected forest areas of Hoang Lien mountain range, with a few saplings growing from seeds. Furthermore, the local farmers continue to impose strong pressure on the remaining primary forest patches, converting it mostly into Bengal cardamom plantations ( Amomum aromaticum Roxb. ) and constructing leisure developments. Thus, the persistence of the species might be at risk in the near future. This species is primarily assessed as Endangered (EN B2a, C2a(i), D) according to the IUCN (2019).

Morphological affinities:— Ophiorrhiza hoanglienensis is most morphologically similar to O. napoensis Lo(1999: 48) and O. fangdingii Lo (1999: 190) , both endemic to southern China (Guangxi and Yunnan provinces), by sharing salverform to funnel form corolla tube, longer than 20 mm and well-developed bracts. However, O. hoanglienensis is clearly distinguished from O. napoensis in having stipules oblong-lanceolate, 9–13 mm long, persistent (vs. triangular, 0.5–1 mm long, caducous), leaves in equal pairs (vs. unequal pairs), bracts lanceolate, 15–20 mm long (vs. lanceolate-linear, 10–14 mm long), calyx lobes reaching 3.2–3.5 mm long at max (vs. reaching 1.8–2 mm long at max), corolla tube ovate to broadly triangular, 25–28 mm long, sparsely hairy at apical part inside (vs. ligulate to ovate corolla, 20–22 mm long, glabrous inside), corolla lobes dorsally ribbed without horn (vs. ribbed with short horn). Furthermore, O. hoanglienensis differs from O. fangdingii by some morphological characters of the stems (green vs. purplish), stipules (oblong-lanceolate, 9–13 mm long, persistent vs. triangular, 2–3 mm long, caducous), leaves (equal pairs, abaxially pale vs. unequal pairs, abaxially pale with brown veins), peduncles (8–13 mm long vs. 15–20 mm long), bracts (lanceolate, 15–20 mm long, acute at apex vs. lanceolate-linear, 10–14 mm long, obtuse at apex), corolla (exclusively white with a 25–28 mm long tube vs. pinkish-white with a 20–22 mm long tube) and corolla lobe dorsally (ribbed without horn vs. narrowly winged, with wing extending into very short horn). Detailed comparisons are provided in Table 1.

Additional specimen examined: VIETNAM. Lao Cai province: Sapa, Ton forest station, Hoang Lien National Park, along dry stream, 14 November 2018, Do Van Truong 151 (VNMN).

Figures

FIGURE 1. Ophiorrhiza hoanglienensis. A. Habit and Inflorescence congested-cymose; B. Stipule entire; C. Stipule cleaved up to ¾ the length; D. Flower bud; E. Bracts well-developed; F. Frontal view of flower; G. Longistylous flower; H. Brevistylous flower; I. Hypanthium subturbinate with unequal calyx lobes. Drawn by Do Van Truong.

FIGURE 2. Ophiorrhiza hoanglienensis. A. Habit and Inflorescence congested-cymose; B. Abaxial leaf surface; C. Stipule cleaved up to ¾ the length (indicated by a red arrow); D. Stipule entire; E. Stigma 2-lobed (indicated by a red arrow); F. Corolla lobes dorsally ribbed without horn (indicated by a red arrow); G. Flowers distylous (longistylous flower indicated by a red arrow; brevistylous flower indicated by a blue arrow); H. Bracts well-developed; I. Dissected longistylous flower; J. Brevistylous flower; K. Hypanthium subturbinate with unequal calyx lobes. Photos by Do Van Truong.