Acer yui W.P. Fang (1934: 235)

Liu, Fu-Rong, Wang, Hai-Feng, Peng, Pei-Hao & Luo, Jian-Xun, 2022, Supplementary description of floral characters and nomenclatural note for the rare maple Acer yui W. P. Fang (Sapindaceae) from western China, Phytotaxa 538 (3), pp. 249-256 : 252-255

Acer yui W.P. Fang (1934: 235) .

≡ A. buergerianum subsp. yui (W.P.Fang) A.E. Murray (1982: 13) , figs. 1–3.

Type:— CHINA. Sichuan [Szechuan]: Jiuzhaigou [Nan-ping hsien], Shaba [Sa-pa], elev. ca. 1950 m, 11 October 1933, T. T. Yü 2672 (SZ00135302, lectotype designated by Fang 1939; isolectotypes CQNM0006335, CQNM0006336, IBSC0002085, PE00023478 & PE00935398) .

= Acer yui var. leptocarpum W.P.Fang & Y.T.Wu in Fang (1979: 79).

Type:— CHINA. Sichuan [Szechuan]: Jiuzhaigou [Nan-ping Hsien], Anlegou [Anlokou], elev. ca. 1550 m, 25 August 1964, C. S. Li (李全 Î) & S. C. Chao (IJ兴ł) 2754 (NWTC, not traced) .

Description with special attention on floral characters:— Deciduous tree 5–10 m tall, diameter of breast height to 30 cm. Bark brownish gray or blackish gray. Branches glabrous; lenticels small on two years or older branchlets; winter buds terminal or axillary, scales numerous, outmost ones glabrous abaxially and ciliate on margin, inner ones pubescent. Leaves developed with or after flowering, petiole 3–7 cm long, mostly dull green to purplish, leaf blade mostly ovate to broadly ovate in outline, 3–7 × 2–6 cm, papery, abaxially yellowish pubescent at vein axils (but usually whitish pubescent when fresh), adaxially glabrous, base rounded or broadly obtuse, margin with two lateral lobes below middle to lower 1/3 from above base (which made the leaves 3-lobed or 3-dentate), rarely with blade integrate and narrowly ovate; lobes margin entire or slightly undulate, middle lobe triangular-ovate, apex acute, lateral lobes similar to the middle lobe and 1/5–4/5 as long as the middle lobe, mostly spreading and usually making about 90° angle sinus on two sides of the blade; primary veins 3, reticulate veins conspicuous abaxially. Andromonoecious ( Fig. 3B ); inflorescence arising from terminal or lateral buds of 1-year-old branchlet, corymbose panicles ( Fig. 3A–C ); peduncles ca. 1 cm long, slender, glabrous; involucrate bracts 1–2 pairs on node of floral branchlet, linear-lanceolate, ciliate along margin, caducous ( Fig. 3D ), to 1.6 cm long and less than 0.5 mm wide (widest at base). Staminate inflorescence 3–4 cm long, 3–4 cm in diameter; pedicel 0.8–2 cm long, slender ( Fig. 3A ); staminate flowers ca. 4 mm in diameter ( Fig. 3I ); sepals 5(–6), obovate, 1.2–1.5 mm long, ca. 1 mm wide, yellowish white, apex obtuse, ciliate along margin ( Fig. 3J ); petals 5, yellowish white, 1–1.5 mm long, 0.3–0.5 mm wide, narrowly spatulate, apex obtuse, base cuneate, sparely ciliate along margin ( Fig. 3K ); disk slightly lobed, glabrous ( Fig. 3L ); stamens 5–8, inserted near inner margin of disk ( Fig. 3L ); filaments glabrous, 2–3 mm long; anthers ovoid, ca. 0.8 mm long; pistillode compressed, caducous. Pistillate inflorescence mostly shorter than staminate ones, 2–3 cm long, with numerous pistillate flowers and a few staminate flowers ( Fig. 3B ); pistillate flowers ca. 4 mm in diameter; sepals and petals similar to those of staminate flower; staminode 5–8; filaments glabrous, 0.8–1 mm long (shorter than sepals; Fig. 3E–H ); ovary glabrous ( Fig. 3E ); styles 2, glabrescent, ca. 0.4 mm long, base united, the free portion curved downward; stigmas 2, simple. Infructescence 5-7 cm long; fruiting pedicel 3–5 mm, slender; nutlets convex, ca. 7 × 5 mm, almost glabrous, veined; wing including nutlet obovate, ca. 2.2 × 1 cm, apex obtuse, wings spreading obtusely (for vegetative and fruiting descriptions also referring to Fang 1939, 1981, Fang & Wu 1981 & Xu et al. 2008).

Phenology:— Flowering is observed in April and fruiting from May to October.

Distribution and habitat: — Acer yui is currently known to be restrictively distributed in northwestern Sichuan (Jiuzhaigou) and southern Gansu (Zhouqu & Diebu) (distribution map see Fig. 4 ). It was observed to grow in dry mountainous areas along streams, in broad-leaved forests, at elevational range of 1800–2250 m.

Conservation status: —According to the IUCN Red List Categories and Criteria ( IUCN 2019), the conservation status of Acer yui has been listed as Endangered (EN, B2ab(iii)) for the severely fragmented distribution and threatened habitat ( Crowley et al. 2020).

Nomenclatural note:— Fang (1934) did not indicate the herbarium where the single gathering T. T. Yü 2672 was deposited when describing Acer yui . He mentioned that the epithet was dedicated to the collector, Te-Tsun Yü (1908– 1986), who was then based at the Science Institute of West China. It was hinted that the specimens of this gathering might be available at the present CQNM, where most of the former Science Institute of West China were bequeathed to ( Hou 2012, Chen & He 2022). There are two duplicates of the gathering T. T. Yü 2672 at CQNM, both bearing identical annotations with handwriting signatures by W. P. Fang in 1933, which should be considered syntypes together with the other available duplicates if there are other duplicates according to Art. 9.6 of ICN ( Turland et al. 2018). Later in a monograph of Chinese maples, Fang (1939) stated that the type of A. yui was deposited at Sci, which stands for the Herbarium of the Biological Laboratory of the Science Society of China, Nanking, China, and most of the materials were left to NAS. Although Fang (1939) erroneously cited the gathering as ‘ T. T. Yü 2633 ’, his statement of herbarium unintentionally validated the lectotypification of this species since only single gathering was cited in the protologue. Now six duplicates of the gathering T. T. Yü 2672 are traceable, and only SZ00135302 bears a label with the project title of “the Herbarium of the Biological Laboratory of the Science Society of China, Nanking, China ”. It is therefore assumed that duplicate SZ00135302 is the lectotype designated by Fang (1939), and it make sense because W. P. Fang was based at Sichuan [Szechwan] University since 1937 ( Anonymous 1947). The fact that Lin et al. (2018) considered the duplicated PE00023478 is the holotype of this species is incorrect.

Similar species and notes:— Morphologically, Acer yui is most similar to A. buergerianum Miquel (1865: 88) in habit, leaf blade shape, infructescence and nutlets, and Murray (1982) has treated it as a subspecies of the latter. From our observation during the field works in Jiuzhaigou County, A. yui could be distinguished from A. buergerianum (specimens cited afterward) in both vegetative and floral characters (comparison between the two species is summarized in Table 1 ).

Acer yui var. leptocarpum was described based on one collection at Anlegou, not far from the type locality of the species type in Jiuzhaigou ( Fang 1979), Sichuan Province, Southwest China. The type material (C. S. Li & S. C. Chao 2754) is deposited at the herbarium of former Gausu [Kansu] Normal University (now Northwest Normal University, Lanzhou, NWTC), and no information concerning the duplicates of that gathering due to the present difficult access to the herbarium. From the field observation we conclude that both the leaf blade and fruit size as described by Fang (1979) falling in with the variation range of the type species, and synonymizing it within A. yui by Xu et al. (2008) is here adopted.

Additional specimens examined:— Acer yui . CHINA. Gausu: Diebu County, Lazikou township to Lazikou, elev. ca. 2110 m, 27 July 1988, Bailong Jiang Exped. 913 (PE); near Lazikou township, elev. 2100–2400 m, 8 June 1999, Bailong Jiang Exped. 1987 (PE); Lazikou, elev ca. 1943, 27 September 2005, A. Aiello et al. 071 (PE). Sichuan: Jiuzhaigou, Yanziya [Yentsuya, formerly recorded as in Sungpan Hsien], elev. ca. 1650 m, 22 October 1937, K. T. Fu 2204 (PE); Zhangzha Town, elev. ca. 2200 m, 25 June 1982, W. H. Li et al. H82-0575 (PE); Baihe Township, Erdaoqiao Village, elev. ca. 1852, 4 October 2018, B. Chen et al. JZG0679 (CDBI); Heihe Township, Baiyushan, elev. ca. 2171 m, 20 April 2019, F. R. Liu et al. JZG1012 (CDBI); Heihe Township, Yanli Village, elev. ca. 1966 m, 21 May 2019, Y. Q. Liu et al. JZG1060 (CDBI); Heihe Township, Dashegou, elev. ca. 1933, 17 April 2020, F. R. Liu et al. JZG1333 (CDBI); Zhangzha Town, Saba village, elev. ca. 2074 m, 19 May 2020, F. R. Liu et al. JZG1349 & JZG1350 (CDBI).

Acer buergerianum . CHINA. Sichuan: Jiuzhaigou County, Yongle Town, Balagou village, elev. ca. 1885 m, 18 September 2018, H. He et al. JZG0017 (CDBI); Anle Township, Anle village, elev. 1650–1700 m, 17 April 2020, F. R. Liu et al. JZG1328 & JZG 1329 (CDBI); Anle Township, Anlezahi village, elev. ca. 1559 m, 18 April 2020, F. R. Liu et al. JZG1354 (CDBI).

Figures

FIGURE 3. Acer yui. A. Male flower branch; B. Female flower branch; C. Inflorescence with staminate flowers; D. Involucrate bracts; E. A pistillate flower; F. Sepals of a female flower; G. Petals of pistillate flower; H. Ovary and staminodes of a pistillate flower; I.A staminate flower; J. Sepals of a staminate flower; K. Petals of a staminate flower; L. Stamens and disk of a staminate flower.

FIGURE 4. Distribution map of Acer yui (green triangle stands for the site with specimen record).