Sorbus prunifolia W. B. Liao & H. J. Jing, 2016

Jing, Huijuan, Fan, Qiang, Guo, Wei & Liao, Wenbo, 2016, Sorbus prunifolia (Rosaceae), a new species from Yunnan Province, China, Phytotaxa 258 (2), pp. 171-178 : 172-177

Sorbus prunifolia W. B. Liao & H. J. Jing , sp. nov. ( Figures 1 & 2 )

Type: — CHINA. Yunnan: Gaoligong mountain , Gongshan County, 2921 m, 98°27 ′ 16 ″ E ; 27°50 ′ 30 ″ N ; 28 July 2008, Y. Yu & W. Guo YN 013 (holotype: SYS! SYS00175831 ; isotypes: SYS! IBSC!) .

Diagnosis: —The new species is morphologically similar to Sorbus aronioides Rehder (1915: 268) but is distinguished by the epiphytic habit, smaller leaves, shorter petioles, 2 styles (not 2–3), densely brownish hairy rachis and pedicels when young (not glabrous), sparsely brownish hairy hypanthium and sepals (not glabrous), and subglobose pome with small lenticels (not ovoid). It is also similar to Sorbus astateria (Cardot) Handel-Mazzetti (1933: 466) but can be clearly distinguished by the epiphytic habit, smaller leaves and flowers, abaxially rusty-brownish tomentose along raised veins when young, gradually glabrate (not both surfaces densely rusty tomentose), shorter petioles and pedicels, only 2 styles (not 3–4), sparsely brownish hairy hypanthium and sepals (without densely rusty tomentose), and subglobose pome with small lenticels (not ovoid).

Epiphytic; shrubs or small trees, 2–4 (–6) m tall. Branchlets slender and stretchy, cylindrical, glabrous, prominent and numerous lenticels, purplish brown when young, purplish black when old; buds ovoid, apex acute or ±obtuse, 2–3 mm long; scales brown or purplish brown, without scarious margin, glabrous. Leaves simple; petiole 3–6 mm, brownish tomentose when young, gradually glabrescent; leaf blade pale grayish green abaxially, green adaxially, ovate-lanceolate, oblong-elliptic, or elliptic-lanceolate, 2.5(3)–5 × 1–2 cm, apex short and acuminate, base cuneate-attenuate, margin serrate, entire near base, lateral veins 6–8 pairs, branched and anastomosing toward margin, abaxially densely rusty-brownish tomentose along raised veins when young, gradually glabrate or sparsely tomentulose only abaxially along midvein. Compound corymbs terminal, 3–4 × 3–3.5 cm, densely flowered, ca. 10; rachis and pedicels distinctly rusty-brownish tomentose when young, with numerous lenticels when old; pedicel 2–5 mm. Flowers 6–7 mm in diam. Hypanthium campanulate, sparsely rusty-brownish tomentose. Sepals triangular, apex acute, abaxially sparsely tomentose, usually spreading, deciduous. Petals white, irregularly ovate or narrowly ovate, 2.5–3 mm long, 2–2.5 mm wide, adaxially sparsely rust-brown pilose, apex obtuse. Stamens 20, nearly as long as or slightly longer than petals; anthers brown, broadly ovate. Styles 2, nearly as long as stamens, glabrous, connate, nearly 1/2 of the length. Fruit subglobose, 8–10 (–12) mm in diam., glabrous at maturity, 2-loculed, with an annular scar and few small lenticels; seeds brown, obovoid, compressed.

Habit: —An epiphyte on tree trunks of Lithocarpus variolosus (Franch.) Chun (1928: 154) and Picea asperata Mast. (1906: 419) .

Phenology: —Flowering from April to May. Fruiting from August to October.

Etymology: —The epithet prunifolia refers to the fact that the leaves of the species look like the leaves of some Prunus species.

Ecology and Distribution: — Sorbus prunifolia is distributed in Yunnan Province of China, known only from Gaoligong Mountain in Gongshan County, Biluo Mountain in Fugong County, and Wutai Mountain in Jinping County. It is an epiphytic shrub on the tree trunks of Lithocarpus variolosus and Picea asperata , growing in coniferous and broad-leaved mixed forests on slopes and under dense forest, at elevations of 2500–3000 m. Associated species are Tsuga dumosa (D. Don) Eichler (1887: 80) , Rhododendron spp. (1753: 392), and Sorbus harrowiana (Balf. f. et W. W. Smith) Rehder (1920: 263) .

Additional collections examined (Paratypes): — CHINA. Yunnan: Gaoligong mountain, Gongshan County, epiphytic, 2921 m, 98°27 ′ 16 ″ E; 27°50 ′ 30 ″ N, 3 Jun 2015, H. J. Jing YN2015010, YN2015011, YN2015012, YN2015013, YN2015014 (SYS!); Biluo Mountain, Fugong County, Tsuga forests on slopes, 2500 ‒ 2700 m, 28 May 1982, Qinghai-Xizang Team 6956 (KUN!), which has been identified as S. aronioides by L. H. Zhou. Correspondingly, the voucher of new species also included the following specimen identified as S. aronioides by Y. M. Shui: Wutaishan, Ma-an-di, Jinping County, Honghe Hani & Yi Autonomous Prefecture. epiphytic, 2600 m, 2 Oct. 1996, S. K. Wu, L. H. Liu et al. 3307 (KUN!).

Notes: —This new species is of interest for its very small leaves and the epiphytic habit, which are rarely recorded in other taxa in sect. Micromeles .

Relationships: —The new species is assigned to section Micromeles because of the old leaves, which are subglabrous abaxially (distinctly rusty-brownish tomentose along raised veins when young, gradually glabrate); the curved secondary veins, which anastomose toward the leaf margin; and the styles, which are connate from base to middle. It is easily distinguished from all the other Micromeles species by the epiphytic growth form and smaller leaves. In the simple-leaved group of Sorbus , only the new species and S. epidendron Handel-Mazzetti (1923: 135) are epiphytic species. However, S. epidendron belongs to sect. Ferrugineae (T. T. Yü) Aldasoro (2004: 61).

The closest relative of Sorbus prunifolia on morphological grounds could be S. aronioides . They share several similar characteristics, e.g., the ovate or elliptic-lanceolate leaves, the brownish hairs on the central and secondary vein of the youngest leaves, and the basally connate styles. Many specimens of S. prunifolia were misidentified as S. aronioides due to these morphological similarities. In fact, S. prunifolia can be readily separated from S. aronioides by the different habit (epiphytic vs. terrestrial), the smaller leaves (2.5–5 × 1–2 cm vs. 6–8 × 2.5–5 cm), the tomentose (vs. glabrous) petioles, rachis and pedicels, the shorter petioles (3–6 mm vs. 5–10 mm), 2–loculed (vs. 2- or 3-loculed, rarely 4-loculed) ovary, and the subglobose (vs. ovoid) fruits ( Table 1 & Figure 3 ). Our examination of the collections in KUN has revealed that a specimen (S. K. Wu, L. H. Liu et al. 3307, collected in Jinping County, Yunnan, China; identified as S. aronioides by Y. M. Shui) exhibits an epiphytic shrub habit with small leaves (2.9–5.3 cm × 1.2–1.8 cm), tomentose petioles and subglobose fruits. Other three fruiting materials collected in the same locality (S. K. Wu, L. H. Liu et al. 3284, 3287, 4170) and one flowering material (Qinghai-Xizang Team 6956 from Biluo Mountain, Fugong County, Yunnan) show the same morphological characters though the habit data were not recorded. Thus we designated these specimens as the paratypes of S. prunifolia .

Another probable close relative of Sorbus prunifolia is S. thomsonii (King ex Hooker f.) Rehder (1915: 277) . However, it differs from S. thomsonii by the leaf margin (sharply serrate vs. shallowly minutely serrate apically) and the tomentose (vs. glabrous) petioles, rachis and pedicels. It is also related to S. astateria ( Sorbus sect. Ferrugineae (T. T. Yü) Aldasoro (2004: 61)) in leaf shape, with tomentum on rachis, pedicels, hypanthium and sepals. According to the classification of Aldasoro et al. (2004), the main differences between sect. Micromeles and sect. Ferrugineae are the indumentum of the leaves, rachis, pedicels, hypanthium and sepals (glabrous vs. densely rusty tomentose). Therefore, S. prunifolia may form a link between S. aronioides (sect. Micromeles ) and S. astateria (sect. Ferrugineae) owing to the intermediate characteristics of the indumentum, as described above.

Figures

FIGURE 1. Sorbus prunifolia W. B. Liao & H. J. Jing A. Fruiting branch; B. Flowering branch; C. Flower with calyx and bracts; D. Calyx; E. Petal; F. Flower, in longitudinal section; G. Fruit. A from Y. Yu & W. Guo YN013 (holotype, SYS); B–F from Qinghai-Xizang team 6956, G from S. K. Wu, L. H. Liu et al. 3307 (Paratype, KUN). Drawn by Ling Wang.

FIGURE 2. Sorbus prunifolia W. B. Liao & H. J. Jing A–B. Living condition (An epiphyte on tree trunks, as indicated by the yellow arrows.); C. Fruit branches. Photos were taken by Huijuan Jing.

FIGURE 3. Specimens of Sorbus aronioides (A) and S. prunifolia (B).