Hedyotis longiramulis Y.D.Xu & R.J.Wang, 2023

Xu, Yi-Da, Zhang, Ying & Wang, Rui-Jiang, 2023, Hedyotis longiramulis (Rubiaceae), a new species from south China, PhytoKeys 230, pp. 271-287 : 271

Hedyotis longiramulis Y.D.Xu & R.J.Wang sp. nov.

Figs 2 , 3 鹅凰嶂耳草 ( é Huáng Zhàng ěr Căo)

Type.

China. Guangdong Province: Yangchun City, Bajia Town , Guangdong Ehuangzhang Provincial Nature Reserve , roadsides, 21°52'N, 111°25'E, elev. 643 m. April 9, 2021, Y.D. Xu & R.J. Wang 6540 (holotype: IBSC [IBSC0865777!]; isotype: IBSC [IBSC0865778!]) .

Diagnosis.

The species is similar to H. caudatifolia in having a subshrubby habit, ovate to lanceolate leaves, and long lateral branches with several terminal and axillary inflorescences, but differs from it by having puberulent, more or less tetragonal and decussately sulcate juvenile stems (versus glabrous and terete in H. caudatifolia ), waxy leaf surface (versus non-waxy in H. caudatifolia ), shorter peduncles (0.5-2.0 cm versus 2.0-10.0 cm in H. caudatifolia ), a higher length ratio of corolla lobe to tube (0.9-1.0 versus approximately 0.8 in H. caudatifolia ), and subglobose capsules (versus ellipsoid-oblong or ellipsoid in H. caudatifolia ).

Description.

Perennial woody subshrubs, 40-120 cm tall. Stem more or less tetragonal and decussately sulcate at juvenile internodes, becoming terete with age, purplish, puberulent, branched at upper part. Leaves opposite, 5-16 × 1.5-4 cm on main stem and 1.0-6.5 × 0.3-1.5 cm on lateral branches, ovate to lanceolate, coriaceous, dark green adaxially, greyish-green or sometimes purplish abaxially, both surfaces waxy, apex acute or subacute, base cuneate or shortly decurrent; petiole 5-15 mm long on main stem and 2-5 mm long on lateral branches, waxy or puberulent; midrib depressed adaxially and prominent abaxially, secondary veins usually 5-6 on each side, sometimes indistinct adaxially; stipules 4-10 × 3-6 mm, triangular, apex acute to acuminate, margin sparsely glandular serrate, puberulent abaxially. Inflorescences growing on long lateral branches, terminal and axillary in the upper nodes, 1.5-3.5 cm long, cymose or paniculate-cymose; inflorescence axes tetragonal, sulcate; peduncles 0.5-2.0 cm long; bracts ca. 1 mm long, subulate. Flowers heterostylous, pedicels 0.9-2.0 mm long. Hypanthium ca. 1 mm long, obconic to subglobose; lobes 4, ca. 0.9 × 0.9 mm, ovate-triangular, blunt or rounded at apex. Corolla white or purplish, tube 3.5-3.8 mm long, glabrous abaxially and densely or sparsely pubescent adaxially; lobes 4, 3.5-3.8 × 1.8-2.2 mm, ovate-triangular; stamens 4, anthers ca. 0.9 mm long; stigma bilobed, ca. 0.5 mm long, subglobose, papillate. Long-styled flowers: stamens included, filaments ca. 0.6 mm long, adnate to the middle part of corolla tube; style ca. 7.6 mm long, exserted, glabrous. Short-styled flowers: stamens exserted, filaments ca. 2.8 mm long, adnate to the throat of corolla tube; style ca. 2.7 mm long, included, glabrous. Fruits capsular, ca. 2.0 mm in diameter, subglobose, glabrous, dehiscent diplophragmously; seeds several, ca. 1 mm long, cymbiform, with reticulate surface. (Fig. 3A-C .)

Distribution and habitat.

Hedyotis longiramulis is only known from Yangchun City of Guangdong Province, China. It grows mainly in damp places under broad-leaved forests, sometimes on roadsides at the elevation of 500-700 m. The associated species are mainly (Hance ex Benth.) Krass. ( Melastomataceae ), Melastoma sanguineum Sims ( Melastomataceae ), Dunnia sinensis Tutcher ( Rubiaceae ), Dicranopteris ampla Ching & P.S.Chiu ( Gleicheniaceae ) and Selaginella doederleinii Hieron. ( Selaginellaceae ).

Phenology.

Flowering from late March to July, fruiting from August to October.

Etymology.

The specific epithet “longiramulis” of the new species refers to its long lateral branches bearing many inflorescences.

Palynology.

The pollen grains of Hedyotis longiramulis are monads, isopolar, spheroidal, 3-colporate; the tectum is a double microreticulum, with a psilate suprareticulum and a microechinate infrareticulum. The pollen size is 22.5 (20.2-25.1) × 21.5 (19.0-22.8) μm with P/E value 1.04 in long-styled flowers (Fig. 3D-F ) and 27.1 (25.2-29.3) × 27.1 (25.1-28.7) μm with P/E value 1.00 in short-styled flowers (Fig. 3G-I ).

Foliar epidermal anatomy.

The epidermal cells on the upper (Fig. 3J ) and lower (Fig. 3K ) surface of leaves of H. longiramulis are irregularly polygonal, randomly arranged and have striated and papillate surface ornamentation, with the striations thickened at the middle of the periclinal walls, and the papillae conical, with granular ornamentation on the surface. The anticlinal walls are straight in epidermis cells of the upper leaf surface and undulate in those of the lower leaf surface.

The leaves of H. longiramulis are hypostomatic, with the stomata randomly orientated over most of the lower surface. The stomata are paracytic, ca. 56.5 (51.4-63.4) × 42.8 (37.1-52.1) μm in size (Fig. 3L ).

Additional specimens examined

(paratypes). China. Guangdong Province: Yangchun City, Guigang Town, Baichong Provincial Nature Reserve , roadside, 13 Sept. 1990, Nian Liu et al. 424 (IBSC) ; ibid., 18 May 1991, Nian Liu et al. 1735 (IBSC). Yangchun City, Bajia Town , Guangdong Ehuangzhang Provincial Nature Reserve , mountain land and valley, 24 Oct. 1957, Kui Liang 69692 (CANT) ; ibid., 23 Oct. 1957, Bao-Han Liang 89654 (CANT) ; ibid., 11 Oct. 1990, Nian Liu et al. 866 and 899 (IBSC) ; ibid., 11 May 2001, Hua-Gu Ye et al. 5629 (IBSC) ; ibid., 7 Apr. 2019, Xin-Xin Zhou et al. ZXX0026 (IBSC) ; ibid., 12 Aug. 2020, Dan Liang et al. WP1366 (IBSC) ; ibid., 10 Sept. 2020, Yi-Da Xu & Fan Su AP 0138 (IBSC) ; ibid., 9 Apr. 2021, Rui-Jiang Wang & Yi-Da Xu 6541 (IBSC) .

Conservation status assessment.

So far 10 subpopulations of Hedyotis longiramulis were found in Yangchun City (AOO 40 km2, EOO 758 km2), Guangdong Province, and their habitats are well protected. About 60 mature individuals were found in each of these subpopulations (within 2 × 2 km grid cells). We therefore estimated that there are at least 600 mature individuals in this area. According to the criteria D1 of IUCN Red List Categories and Criteria (IUCN 2022), the species can be assessed as “Vulnerable”. However, many other subpopulations of this species may be found in similar habitat nearby the vouchers’ localities in the nature reserves. Considering that this species has no economic uses and that there are no plausible threats since it occurs in two protected reserves, we recommend to evaluate it as "Least Concern".

Figures

Figure 2. Hedyotis longiramulis Y. D. Xu & R. J. Wang A habit B habitat C inflorescences D part of stem (right) and its transverse section E adaxial (left) and abaxial (right) surgaces of leaf F Stipules G long-styled flower (left) and its longitudinal section (right) H short-styled flower (left) and its longitudinal section (right) I infructescence J diplophragmous capsule K dorsal (left) and ventral (right) view of seeds.

Figure 3. Micromorphology of seed, pollen and leaf epidermis of Hedyotis longiramulis using SEM A-C ventral view, dorsal view, and surface ornamentation of seeds, respectively D, G, E, H, F, I equatorial view, polar view, and reticulate ornamentation of pollen grains, respectively J-L leaf epidermis, adaxial and abaxial surfaces, and stomatal apparatus, respectively A-C, J-L Yi-Da Xu & Fan Su AP 0138 D-F Rui-Jiang Wang & Yi-Da Xu 6540, long-styled flower G-I Rui-Jiang Wang & Yi-Da Xu 6541, short-styled flower.