Rhamnella brachycarpa Z. Qiang Lu & Y. Shuai Sun, 2019

Lu, Zhiqiang & Sun, Yongshuai, 2019, Rhamnella brachycarpa (Rhamnaceae), a new species from Hainan Island, China, PhytoKeys 132, pp. 19-29 : 19

Rhamnella brachycarpa Z. Qiang Lu & Y. Shuai Sun sp. nov. Figures 3 , 4

Diagnosis.

Rhamnella brachycarpa differs from R. rubrinervis and R. tonkinensis by leaf length to width ratio of 1.9-2.4 (compared to 2.5-3.9 in the related species) and dried fruit 6.5-7.5 × 4.7-6.0 mm in size (compared to 8.2-11.1 × 4.2-5.8 mm in R. rubrinervis and R. tonkinensis ) with length to width ratio of 1.3-1.5 (compared to 1.6-2.2).

Type.

CHINA. Hainan: Baoting County, Xian’an, 109°25'34"E, 18°35'37"N, 650 m alt., forest edge, 16 Oct 2018, Z.Q. Lu 2018HN3001 (holotype, HITBC; isotypes, HITBC and GXMG).

Description.

Small trees or climbing vines, evergreen. Young branches sparsely pilose or glabrous; older branches reddish-brown, grey-brown or grey, glabrous. Leaves alternate; stipules lanceolate, persistent; petiole 0.7-1.2 cm long, glabrous, narrowly grooved on the upper surface; leaf blade abaxially dark green, shiny, adaxially pale green, elliptic-ovate, 5.8-10.3 × 3.1-4.8 cm, leathery, abaxially glabrous, adaxially glabrous, lateral veins 5-7 pairs, slightly impressed abaxially, prominent adaxially, base cuneate or nearly rounded, margin subentire, conspicuously serrate when seedlings, apex shortly acuminate or acute. Flowering branches axillary, rarely not, 7-18 cm long, glabrous. Flowers bisexual, ca. 4 mm diam., 4- or 6-merous, few to 2 or 9 in axillary cymes, subsessile or shortly pedunculate at bracteole leaf of flowering branches; bracteole leaf similar to leaves in vegetative branches, but smaller, 1.5-5.0 × 0.9-2.3 cm. Pedicel 3.3-5.2 mm long, glabrous. 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, 8.7-10.9 × 7.5-10.6 mm, 6.5-7.5 × 4.7-6.0 mm when dried, base with persistent calyx tube; fruiting pedicel 4.3-6.2 mm, glabrous, 1-loculed, 1-seeded; seed dumpy, apex mucronate, smooth on the surface, 5.0-7.0 × 4.5-5.5 mm.

Etymology.

In contrast with relatives, all individuals from these distinct Hainan populations have shorter fruit; we therefore give the epithet Rhamnella brachycarpa .

Phenology.

Flowering from May to September and fruiting from July to October.

Habitat, distribution and conservation.

According to our field surveys and records in Chinese Virtual Herbarium (CVH), R. brachycarpa has been found at three sites on Hainan Island (Baoting County: Xian’an and Shijia; Qionghai City: Tayang). Only two small populations with 45 individuals (including only 22 mature trees) have been found in Baoting, while no extant tree has been found in the Qionghai population due to the destruction of the habitat. Of the two small populations in Baoting, with a separation distance of about 900 m, one consists of only three mature trees without seedlings; the second population has 19 mature trees and 23 immature trees. All mature trees are more than 3.1 m in height and less than 1.8 m is observed for all immature trees. Forty five individuals of this new species sparsely grow along the roadsides and in forest edges or thick forest. Mature trees with climbing habit only grow in thick forest or forest edges with high canopies, but those with erect habit prefer to grow along roadsides or in forest edges without high canopies. Nevertheless, all these immature trees, sparsely growing along the roadsides and in forest edges or thick forest, present the erect habit. The rarity of this new species may be partially due to human activity because the habitat is also suitable for cultivating rubber trees and other economic plants. Comparing to the number of mature trees, the number of immature trees further indicates a decreasing population trend. In addition, all these trees are distributed in a total area of approximately 0.7 km2. No population was found during repeated field surveys of the surrounding areas. According to the IUCN Categories and Criteria ( IUCN 2016), the species is classified as "Critically Endangered" (CR). Therefore, it will be necessary to pay close attention to the conservation of this new species.

Additional specimens examined.

CHINA. Hainan: Qionghai City, Tayang, open forest, 27 Nov 1936, X.Q. Liu 28256 (PE); Baoting County, Xian’an, 109°25'34"E, 18°35'37"N, 650 m alt., forest edge, roadside and thick forest, 16 Oct 2018, Z.Q. Lu 2018HN3002 - Z.Q. Lu 2018HN3012 (HITBC); Baoting County, Shijia, 109°25'42"E, 18°36'02"N, 680 m alt., forest edge, 17 Oct 2018, Z.Q. Lu 2018HN3013 - Z.Q. Lu 2018HN3015 (GXMI).

Figures

Figure 3. Rhamnella brachycarpa Z. Qiang Lu & Y. Shuai Sun, sp. nov., drawn from the tree of Z. Q. Lu 2018 HN 3001.

Figure 4. Rhamnella brachycarpa Z. Qiang Lu & Y. Shuai Sun. A The habitat B Branches with leaves and fruit C Fruit D Seeds.