Rhamnella intermedia Z. Qiang Lu & Y. Shuai Sun, 2020

Lu, Zhiqiang & Sun, Yongshuai, 2020, Rhamnella intermedia (Rhamnaceae), a new evergreen species from southwest Guangxi, PhytoKeys 159, pp. 115-126 : 115

Rhamnella intermedia Z. Qiang Lu & Y. Shuai Sun sp. nov. Figures 1 , 2

Diagnosis.

Rhamnella intermedia differs from R. rubrinervis and R. tonkinensis by smaller size of dried fruit (6.0-7.0 × 4.7-5.3 vs. 7.5-11.1 × 4.2-5.8 mm) and seeds (5.5-6.5 × 4.5-5.0 vs. 7.0-9.9 × 4.2-5.5 mm) and smaller ratio of length to width of dried fruit (1.3-1.5 vs. 1.6-2.2) and seeds (1.2-1.4 vs. 1.6-2.1), and from R. brachycarpa by the larger ratio of length to width of leaves (2.7-3.8 vs. 1.9-2.4), smaller length of leaf petioles (3-8 vs. 7-12 mm), larger length of fruiting pedicels (5-9 vs. 4-6 mm), leaf apices acuminate to long acuminate and seed apices rarely mucronate. In addition, the characters of densely pilose young branches can also significantly separate this new species from R. rubrinervis .

Type.

China. Guangxi: Pingxiang County, 22°07'19"N, 106°44'40"E, 298 m altitude, karst limestone hill, 5 Oct 2019, Z.Q. Lu 2019YG2601 (holotype, GXMI; isotypes, HITBC).

Description.

Shrubs or small trees, rarely climbing vines, evergreen. Young branches densely pilose; older branches grey-brown or grey, sparsely pilose or glabrous. Leaves alternate; stipules subulate, persistent; petiole 0.3-0.8 cm long, densely pilose when young, late sparsely pilose, rarely glabrous, narrowly grooved on the upper surface; leaf blade abaxially dark green, shiny, adaxially pale green, oblong or ovate-oblong, 6.4-13.0 × 2.0-5.0 cm, length-width ratio 2.7-3.8, leathery, abaxially sparsely pilose or glabrous, sparsely pilose along leaf veins or glabrous, adaxially glabrous, lateral veins 6-7 pairs, slightly impressed abaxially, prominent adaxially, base commonly rounded, rarely cuneate, margin inconspicuously remotely serrate or subentire; apex acuminate to long acuminate. Flowering branches axillary 8-13 cm long, densely or sparsely pilose, rarely glabrous. Flowers bisexual, ca. 4 mm diam., 5-merous, few to 10 in axillary cymes, cymes subsessile or shortly pedunculate at bracteole leaf of flowering branches; bracteole leaf similar to leaves in vegetative branches, but smaller, 3.5-6.5 × 1.3-2.0 cm, lateral veins 3-5 pairs. Pedicel 4.0-7.0 mm long, densely or sparsely pilose. Sepals triangular, ca. 2 mm, adaxially midvein raised, rostellate at lower middle. Petals obovate, shortly clawed. Stamens involute by petals, ca. 2 mm long. Disc rounded, thick. Ovary globose, not immersed in disc. Drupe purple-red or orange at maturity, ovoid-cylindrical or globose, 8.5-10.2 × 8.2-10.1 mm, 6.0-7.0 × 4.7-5.3 mm when dried, base with persistent calyx tube; fruiting pedicel 5.0-9.0 mm, sparsely pilose, 1-loculed, 1-seeded; seed short, apex rarely mucronate, smooth on the surface, 5.5-6.5 × 4.5-5.0 mm, length-width ratio 1.2-1.4.

Etymology.

Owing to its intermediate morphology compared to the other three closely related species, we provide the epithet intermedia .

Phenology.

Flowering from June to September and fruiting from August to October.

Habitat and distribution.

To date, only two R. intermedia populations have been collected from southwest Guangxi. For its population census, more than 20 mature trees (3-6 m in height) and a large number of seedlings grow on the karst limestone hill. We also found that six individuals present a climbing habit at locations where there is a relative high canopy; however, all others are erect. Interestingly, they shared the same ITS types between erect and climbing trees, suggesting no genetic differentiation. In addition, this new species may be also distributed in Vietnam, because it is found in Pingxiang and Daxin from southwest Guangxi, which is close to Vietnam. Further field investigations on its entire distribution are recommended in the future.

Additional specimens examined.

China. Guangxi: Pingxiang County, 22°07'19"N, 106°44'40"E, 298 m altitude, karst limestone hill, 5 Oct 2019, Z.Q. Lu 2019YG2602 - Z.Q. Lu 2019YG2619 (HITBC); Daxin County, Wude Township, 22°34'15"N, 106°44'56"E, 276 m altitude, along road, 27 May 2018, Z.Q. Lu 201810801 (HITBC); the same locality: 26 August 2018, Z.Q. Lu 201810802 (HITBC). Longzhou County, Daqingshan, hillside, July 1953, Guangxi team 2967 (PE).

Notes.

R. intermedia is morphologically similar to R. rubrinervis based on leaf characters, but they can be easily distinguished between each other by fruit and seed characters. However, it also can be significantly distinguished from R. rubrinervis by the densely pilose young branches, if the specimen has no fruit and seeds. In addition, it also needs to be mentioned that the flower of R. brachycarpa is 5-merous.

Figures

Figure 1. Rhamnella intermedia Z. Qiang Lu & Y. Shuai Sun. A The whole plant, habitat and two geographical locations B flowering branches C a young branch with the persistent stipule D branches with leaves and fruit E dried fruit F mature seeds.

Figure 2. Rhamnella intermedia Z. Qiang Lu & Y. Shuai Sun, sp. nov., drawn from Z. Q. Lu 2019 YG 2601.