Sorbus calcicola W. B. Liao et W. Guo, 2016

Guo, Wei, Fan, Qiang, Jing, Huijuan, Hu, Xiu & Liao, Wenbo, 2016, Sorbus calcicola (Rosaceae), a new species from Guangxi Province in China, Phytotaxa 261 (3), pp. 260-266 : 261-265

Sorbus calcicola W. B. Liao et W. Guo , sp. nov. (Fig. 2 & 3)

TYPE:— CHINA. Guangxi: Huangjiang County, Mulun National Nature Reserve, Zhonglun , on the top of a hill, 835 m, 25°08 ′ 28.51 ″ N, 107°55 ′ 35.76 ″ E, 9 April 2015, W. Guo 956 (holotype SYS; isotypes IBSC) .

Trees or shrubs, 3–4 m tall. Branchlets purplish brown when young, grayish brown when old, terete; grayish white tomentose when young, glabrous when old; buds ovoid, 0.4–0.7 cm, apex acute. Leaves simple; petiole 0.2–0.4 cm, white tomentose; leaf blade elliptic, elliptic-obovate, or ovate, 3–5 × 1.5–2 cm, both surfaces puberulent when young, adaxially glabrate when old, abaxially also glabrate but with few tomentose hairs in axils of veins when old, lateral veins 5–6 pairs, nearly parallel and terminating in marginal teeth, slightly raised abaxially and impressed adaxially.

Inflorescences in corymbs, 1–2 × 2–2.5 cm, 3–7-flowered, rachis and pedicels white tomentose. Flowers 0.8–1.0 cm in diam; pedicels 2–3 mm. Hypanthium campanulate, abaxially densely white tomentose. Sepals long triangular, 2–3 mm, apex acute. Petals white, ovate or triangular-ovate, ca. 4 × 3 mm. Stamens 18–20, shorter than or nearly as long as petals. Styles 2–3, basally connate and white tomentose. Fruit subglobose, 5–8 mm in diam., sparsely gray tomentose at base and apex when young, with or without few small lenticels, sepals persistent.

Phenology:—Flowering from March to April and fruiting from June to September.

Diagnosis and relationships: — Sorbus calcicola is closely related to Sorbus pallescens ( Rehder 1915: 266) , Sorbus thibetica ( Cardot 1918: 349) Handel-Mazzetti (1933: 467) and Sorbus cuspidata ( Spach 1834: 106) Hedlund (1901: 89) . But it can be easily distinguished from the above similar species mainly by the shorter petiole (2–4 mm long), smaller leaf blade (3–5 × 1.5–2 cm), fewer lateral veins (5–6 pairs), shorter and narrower corymbs with only 3–7 flowers (1–2 × 2–2.5 cm). Characters to differentiate S. calcicola and the other three similar Sorbus species are summarized in Table 1.

Distribution and habitat:— Sorbus calcicola is currently known only in the karst landform of Mulun National Nature Reserve in Huangjiang County, Guangxi Province, China. The species mainly grows at sunny thickets on the top of rocked hills at about 835 m above sea level, and 50 meters below the peak with sporadic distribution. Two adjacent hills were investigated. And each site more then thirty trees were found including the diameter of 8 cm trees, young trees and even some seedlings which suggested that a reasonable population structure was distributed for the species. The surrounding forests for the species all belonging to the Mulun National Nature Reserve are being protected well. And nearby residents have been moved out in the survey and surrounding areas. The local associated species include Eriobotrya seguinii (H. Léveillé) Cardot ex Guillaumin , Spiraea kwangsiensis T. T.Yu , Fokienia hodginsii (Dunn) A. Henry & H. H. Thomas , Litsea elongata (Nees) J. D. Hooker , Cyclobalanopsis gracilis (Rehder & E. H. Wilson) W. C. Cheng & T. Hong and Photinia lochengensis T. T. Yu. However , the closely related species for S. calcicola are mainly distributed in the southwest of China with S. pallescens recorded in west of Sichuan, south of Xizang and northwest of Yunnan; S. cuspidata in Xizang; S. thibetica in northwest of Yunnan and southeast of Xizang ( Lu & Stephen, 2003).

FIGRUE 1. The Bayesian 50% majority rule consensus tree based on nrITS datasets.

Notes: The parsimony strict consensus tree (270 steps, CI=0.6778, RI= 0.8415) is similar to the Bayesian tree but less resolved. Numbers above the branches are Bayesian posterior probabilities and numbers below are parsimony bootstrap values.

FIGRUE 2. Sorbus calcicola W. B. Liao et W. Guo , sp. nov. A. Fruit branch. B. Flowering branch; C. Fruit in cross section ; D. Fruit; E. Petal ; F. Flower ; G. Style (Drawn by Yunxiao Liu from the holotype) .

Discussion: —The phylogeny analyses indicated that S. calcicola and S. pallescens form a clade with S. cuspidata , S. thibetica , S. coronata (Cardot) T. T. Yü & H. T. Tsai and S. hemsleyi (C. K. Schneider) Rehder. The clade shares morphological features including fruit apically with persistent sepals, carpels mostly adnate to hypanthium but only separate at apex. However, the characters for S. calcicola including leaves abaxially glabrous or tomentose in vein axils, lateral veins 5–6 pairs and corymbs inflorescence with only 3–7 flowers are obviously different from other species. In all, S. calcicola should be treated as a distinct new species combined with the morphological differences and the molecular phylogenetic results.

FIGRUE 3. Sorbus calcicola W. B. Liao et W. Guo , sp. nov. A. Fruit branch; B. Flowering branch; C. Fruit persistent in last year; D. Flower; Photos taken by Guo Wei.

FIGRUE 4. Known distribution of Sorbus calcicola and related species in China.