Saxifraga viridipetala, Gao, Qingbo, Zhang, Zhuoxin, Chen, Shilong & Gornall, Richard J., 2018

Gao, Qingbo, Zhang, Zhuoxin, Chen, Shilong & Gornall, Richard J., 2018, A new species of Saxifraga in section Ciliatae subsection Gemmiparae (Saxifragaceae) from Sichuan province, China, Phytotaxa 333 (2), pp. 228-234 : 230-233

Saxifraga viridipetala Z-X. Zhang & Gornall, sp. nov. ( Figs. 1 and 2 )

Type:— CHINA. Sichuan: Huili xian, Xiaoheiqing xiang, open ground of forest, 2315m, 26°36 ′ 26.8 ″ N, 102°02 ′ 46.9 ″ E, 19 September 2015, Gao 2015006 (holotype HNWP; isotype HNWP) .

Description:—Herbs perennial, cespitose, 5–26 cm tall. Stem many branched, proximally and medially brown or white eglandular villous (hairs ca. 1 mm long), distally short glandular hairy. Proximal cauline leaves reduced, often scale-like, sessile, ca. 3 × 1.5 mm, subtending axillary leafy buds. Median cauline leaves aggregated into a distinct rosette, sessile; leaf blade narrowly elliptic to oblanceolate, 7 ‒ 29 × 2 ‒ 9 mm, base cuneate, apex acute, adaxial surface strigose, abaxial surface glabrous and shining silvery-striate when dry, margin entire, cartilaginous, eglandular setoseciliate. Distal cauline leaves reduced, narrowly elliptic, 5 ‒ 20 × 0.5 ‒ 5 mm. Cyme usually corymbose, 5 ‒ 25 mm, 2 ‒ 8 flowered; pedicels 2 ‒ 20 mm, short glandular hairy. Sepals erect to spreading, ovate to triangular, 2 ‒ 4 × 1 ‒ 2 mm, abaxial surface eglandular hairy, adaxial surface and margin glabrous; veins 3 ‒ 7, confluent at apex, apex acute. Petals pale green, purple spotted except towards the tip, narrowly elliptic, remote from each other, 2 ‒ 5 × 1 ‒ 2 mm, 2 ‒ 4- callose, 3 ‒ 7-veined, base contracted into a claw ca. 1 mm, apex subobtuse or acute. Stamens 10, ca. 4 mm, filaments linear, anthers reddish-pink. Ovary subsuperior, ovoid, 2 ‒ 3.5 mm, encircled proximally by a greenish or greenishyellow nectary disc; styles 2, ca. 1.5 ‒ 3 mm.

Distribution and habitat:— Saxifraga viridipetala is known so far only from the type locality in south-western Sichuan province in China, where it is sympatric with S. gemmipara . It grows on rocks and cliffs in forest clearings and margins or in the open, at an altitude of ca. 2300 m.

Phenology:—Flowering occurs from September to October.

Etymology:—The specific epithet refers to the green petals.

Relationships:—The new species has stems with axillary leafy buds subtended by the proximal leaves and a median rosette of leaves whose abaxial surface is silvery-striate ( Fig. 2c ). These features indicate a position in section Ciliatae Haworth (1803: 160) subsection Gemmiparae Engler & Irmscher (1912: 140) . It is closest morphologically to S. gemmipara Franchet (1896: 262) , from which it is indistinguishable in the vegetative state. In flower, however, it produces remote (i.e. separated and not contiguous or overlapping), pale green petals whose adaxial surface is spotted with purple in the proximal 4/5, and which are arranged such that the sepals are exposed to full view from above ( Fig. 2e ). Furthermore, a greenish nectary disc encircles the proximal portion of the ovary ( Fig. 2d ). This is in contrast to S. gemmipara , in which the petals are contiguous, white, typically spotted yellow, green or purple in the proximal half only, and which tend to obscure the sepals when viewed from above; the nectary tissue encircling the base of the ovary is not differentiated into a disc. We believe that these differences in floral morphology are sufficient to establish the taxon as a new species rather than as an infra-specific variant of S. gemmipara . Phylogenetic analysis based on the combined dataset of trn L-F and ITS sequences support the phylogenetic position of S. viridipetala in subsect. Gemmiparae , sister to S. gemmipara ( Fig. 3 ), in agreement with the morphological data.

Green petals are unusual in the genus Saxifraga , occurring in section Ciliatae only in S. hirculoides Decaisne (1841: 67) , where they were erroneously reported as yellow by Pan et al. (2001). Petals of a greenish hue are otherwise found in a very few species, but occur in the chiefly European section Saxifraga , viz. S. paradoxa Sternberg (1810: 22) , S. seguieri Sprengel (1807: 40) , S. aphylla Sternberg (1810: 40) , S. cespitosa Linnaeus (1753: 404) and some variants of S. exarata Villars (1779: 47) and its relatives.

Figures

FIGURE 1. Saxifraga viridipetala Z-X. Zhang & Gornall. A. Plant. B. Adaxial leaf surface. C. Flower. D. Abaxial sepal surface. E. Adaxial sepal surface. F. Petal. All from the holotype Gao2015006 (HNWP). Drawn by Chen Zhang (Nanjing Xiaozhuang University).

FIGURE 2. Saxifraga viridipetala. a) whole plant showing cespitose habit; b) stems in vegetative phase with distal leaf rosettes; c) abaxial surface of rosette leaves, showing silvery-striation; d) original photograph of a flower; e) inflorescence with one open flower. Photographs by Qingbo Gao (a, e), Zhenguo Dong (d) and Zhuoxin Zhang (b, c).

FIGURE 3. Fifty percent strict consensus tree based on the concatenated sequences of trnL-F and ITS from Saxifraga viridipetala and additional 104 Saxifraga species. Numbers on the branches are bootstrap values from maximum parsimony (left) and maximum likelihood (middle) analyses and posterior probabilities (right) from Bayesian inference.