Spiraea fangii H.Y.Hu et X.J.He, 2016

Hu, Hao-Yu, Tan, Jin-Bo, Xie, Deng-Feng, Zhang, Jian & He, Xing-Jin, 2016, Spiraea fangii (Rosaceae), a new species from Sichuan, China, Phytotaxa 268 (2), pp. 155-162 : 156-161

Spiraea fangii H.Y.Hu et X.J.He sp. nova ( Figs. 1–2 )

Diagnosis:—The new species is most similar to Spiraea myrtilloides , but is distinct by having long prostrate branches sometimes rooting, follicles publerulous on adaxialy suture near apex, short branchlets with fascicled leaves and abaxially sparsely pilose near margins.

Type:— CHINA, Sichuan: Dayi County, Heishuihe Nature Reserve, Qi-zi Summit , on alpine screes of sunny slope, elev. 3604 m, 21 October 2015 Hao-Yu Hu & Jian Zhang, hhy2015102101, flowering & fruiting (holotype SZ ; isotype SZ ).

Shrubs deciduous, 0.1–0.3 m tall, with long prostrate branches sometimes rooting, irregularly branched. Long branchlets red-brown, turning brown-gray when old, terete or slightly angled, glabrous, stem bark longitudinally fissured when old; short branchlets gray, with dense triangular residual petioles; buds ovoid, 0.2–0.4mm, with several scales, pubescent on margin, apex acute. Leaves fascicled on short branchlets; petiole 0.5–1mm, glabrous; leaf blade ovate, 2–4 × 4–6 mm, abaxially sparsely pilose, glabrous near veins and lower, adaxially greenish, glabrous, margin entire or 1–2 obtuse near apex. Racemes umbellate, 1–2 × 1–3 cm, 2–5 or single flowered; rachis and pedicels glabrous or sparsely pubescent; pedicels 2–5 mm; bracts linear or lanceolate, 2–3 mm, glabrous. Flowers 3–5 mm in diam. Hypanthium campanulate, glabrous. Sepals triangular, 0.5–1mm, apex acute, spreading or reflecting in fruit. Petals white, suborbicular, 2–3mm, apex obtuse or with a tiny concave. Stamens 20, equaling or shorter than petals. Disk annular, 10-lobed, lobes triangular-ovate, apex emarginated. Carpels glabrous or slightly publerulous on adaxialy suture near apex; styles shorter than stamens. Follicles spreading, glabrous or slightly publerulous on adaxialy suture near apex; styles terminal, divergent.

Etymology:—The specific epithet honors the late Professor Wen-Pei Fang (1899–1983), one of the greatest taxonomists in China who dedicated his life to the study of Chinese flora and the development of Sichuan University Plant Herbarium (SZ).

Phenology:—Flowering from July to August and fruiting from September to October.

Distribution and habitat:— Spiraea fangii is known only from its type locality, Heishuihe Nature Reserve, Sichuan Province, southwest China. It was observed to grow in narrow stone crevices or among rocks on alpine screes of sunny slopes, at an elevation of ca. 3600 m a.s.l.

Discussion:— Spiraea fangii was found in an unusual habitat of alpine screes that has been rarely reported in the genus Spiraea . Similar habitats have been observed in some species such as S. alpina Pallas (1784) , S. myrtilloides and S. daochengensis L.T. Lu (1989) . However, despite of sharing habitats in high elevations, the latter species mostly grow in habitats with higher humidity and weaker wind, e.g., around alpine lakes and streams, alpine bushes, and meadows. The new species is known to grow only on alpine screes of sunny slopes at an elevation of approximately 3600 m. Comparatively speaking, these environments have apparent lower humidity, relatively higher UV intensity and stronger wind. Plant individuals usually reduce heights with increase of elevation gradient in order to adapt to the alpine habitats and sometimes they bear adventitious roots to fix themselves tightly in strong wind ( Körner et al. 1989). As we found in the field work, the new species has a procumbent plant shape and with long prostrate branches sometimes rooting. This particular habit form has never been reported before in this genus. Furthermore, some unique characters of leaf blade was found in SEM observations ( Fig. 3 ); that is, the stomata being present only on the adaxial surface and with risen shape. This stomata occurrence pattern and morphological characters have been reported as a character adapt to high mountains (David 1978, Körner et al. 1989).

Morphologically, Spiraea fangii is similar to S. myrtilloides at first glance by sharing ovate leaf blade, umbellate racemes and spreading follicles. However, the new species can be easily distinguished from S. myrtilloides due to its procumbent habit, adventitious root, leaves fascicled on short branchlets, leaf blades abaxially sparsely pilose near margin, racemes only 2–5-flowered, glabrous follicles, disk lobes apex emarginated and olivary seeds. Some additional characters under SEM observations also show significant difference. The cuticular membrane of S. fangii has papilla on the adaxial surface and striate ridges on the abaxial surface while S. myrtilloides has irregular ridges on both sides. Besides of the surface ornamentation, trichomes also show some difference. Leaf blades of S. fangii are sparsely pilose on abaxial surface and on margins but glabrous on adaxial surface while those of S. mrytillioides are only pilose on margins ( Table 1 ).

There are also several species documented that can occur at elevations up to 4000 m or higher, e.g., Spirarae alpina , S. schneideriana , S. mollifolia , S. arcuata , etc. However, our observations in the field and the herbarium study indicated that this new species has clear difference in multiple morphological characters (see Table 2 , voucher specimens see appendix 1).

Figures

FIGURE 1. Spiraea fangii A. Habitat in alpine screes. B. Habit. C. Inflorescence and flowers. D. Fruit. E. Adventitious root, bar=5mm. F. Short branch covered with residual petioles, bar=1mm. G. Leaves fascicled on short branchlets, bar=2mm.

FIGURE 2. Spiraea fangii A. Habit. B. Short branch. C. Adaxial of leaf blade. D. Abaxial of leaf blade. E. Flower F. Fruit.

FIGURE 3. Micromorphological characters of Spiraea fangii and S. myrtilloides A: S. fangii (from the isotype), B: S. myrtilloides (from hhy-20120824-01,SZ). (1–2. Adaxial of leaf blade. 3–4. Abaxial of leaf blade. 5. Stomata. 6. Follicle. 7. Seeds)