Aster oliganthus W.P. Li & Z. Li, 2017

Li, Zhi, Yin, Gen-Shen, Tang, Ming & Li, Wei-Ping, 2017, Aster oliganthus (Asteraceae, Astereae), a new species from western Sichuan, China, based on morphological and molecular data, Phytotaxa 326 (1), pp. 54-62 : 57-61

Aster oliganthus W.P. Li & Z. Li , sp. nov. ( Figs. 2 and 5 )

Type:— CHINA. Sichuan, Tianquan, Mt. Erlangshan, 29°51ʹ N, 102°19ʹ E, forest margins, 2153 m, 2 September 2016, LWP1608201 (holotype HNNU).

Herbs perennial, 20–115 cm tall, solitary or sometimes caespitose. Rhizomes slender, up to ca. 20 cm. Stems ascending or erect, usually branched in upper part, subglabrous in lower to middle parts, sparsely hispidulous in upper parts and densely pubescent on synflorescence branches. Leaves basal and cauline, 3-veined above base (triplinerved). Basal leaves ovate, on long and narrowly winged petioles, papery, densely pubescent, dark reddish-purple beneath, withered by anthesis. Cauline leaves thinly papery, adaxially subglabrous or sparsely hispidulous, linear-lanceolate, oblonglanceolate or narrowly lanceolate, usually falcate; apex long acuminate to caudate; midvein prominent abaxially; margin shallowly toothed in 3–8 pairs; lower leaves 4–16 × 0.7–2 cm, petiole 0.2–1.2 cm, withered at anthesis; middle leaves (0.3–)0.6–1.7(–2.7) × 4.4–15.2 cm, shortly petiolate to sessile; upper leaves 0.5–1.5 × 4.5–13.5 cm, shortly petiolate to sessile. Capitula 18–339 in terminal paniculate-corymbiform to corymbiform synflorescences, shortly pedunculate. Involucres campanulate, 2–4 mm in diameter. Phyllaries 3–5-seriate, imbricate, herbaceous; apex rounded to acute and ± deep green; midvein greenish and abaxially glabrate to villosulous; margin narrowly to broadly scarious, erose and ciliate; outermost phyllaries ovate to lanceolate, 0.9–2.6 × 0.4–0.8 mm, second-row phyllaries oblong, 1.6–2.6 × 0.6–1 mm, third-row phyllaries oblong, 2.2–4.6 × 0.8–1.1 mm, fourth-row phyllaries oblong, 2.5–5.6 × 0.7–1.3 mm, inmost phyllaries oblong or obovate-oblong or oblong, 4.0–4.4 × 0.8–1 mm. Disk florets yellow, 4–6.5 mm, tube base flared, limb campanulate, 2.2–4 mm, base sparsely strigillose, lobes spreading, narrowly triangular, 1.3–2 mm, glabrous, sparsely to moderately minutely stipitate-glandular. Ray florets 5–7(–9), white, glabrous, eglandular; tube 2–2.6 mm; lamina 3.1–8.3 × 0.4–2.3 mm, shallowly 2–3-lobed. Disk florets 2–5, yellow; tube 2.2–3.6 mm, hairy, lobe 0.7–1.3 mm, recurved; stigmatic appendage (style branch appendage) lanceolate, 0.7 mm, stigmatic lines 0.53–0.83 mm. Achenes oblong, slightly compressed, 0.7–1.5 mm, strigose, 2-ribbed. Pappus dirty white or brown, 2.5–4.3 mm. Fl. and fr. Jul–Dec.

Etymology: —The specific epithet reflects the lower flower number per capitulum in the new species, in comparison to the related A. ageratoides ( Table 1; Figs. 2a , 5 ).

Distribution and Habitat: — Aster oliganthus is currently known only from the eastern margin of the Mt. Hengduan region, Mt. Erlangshan in Tianquan County and Mt. Donglashan in Baoxing County, western Sichuan, China ( Fig.1 ). It grows at the forest margins and along roadsides at elevations of 1500–2200 m above sea level, in shade or half-shade and in wet habitats on steep slopes, rock walls and cliffs ( Fig. 2D ).

Phenology: — Aster oliganthus flowers from late July to October, and produces fruits from late September.

Additional specimens examined (paratypes): — CHINA. Sichuan: Tianquan, Mt. Erlangshan , forest margins, 1500 m, 30 October 2012, LWP 1208006-09 ( HNNU) ; 1900 m, 10 October 2005, LWP0508097-98 ( HNNU) ; 2153 m, 2 September 2016, LWP1608202-35 ( HNNU) ; Tianquan , 4 September 1939, F. C. Tai & C. M. Teng 4370 ( PE) ; Baoxing, Mt. Donglashan , forest margins, 1980 m, 30 July 2016, LWP1607028-44, LWP1607046-49 ( HNNU) ; Baoxing, Mt. Donglashan , 30°28ʹ N, 102°41ʹ E, forest margins, 1980 m, 30 July 2016, LWP1607045 ( HNNU) .

Discussion: — Aster oliganthus is similar to A. ageratoides in habit, triplinerved leaves, lower and basal leaves withering at anthesis, terminal paniculate-corymbiform to corymbiform synflorescences, and 3–5-seriated phyllaries, and, specially, to A. ageratoides var. micranthus in being diploid (2 n = 2 x =18) ( Li & Liu 2005) and in having thinly papery and linear-lanceolate leaves. The new species could be easily distinguished from A. ageratoides var. micranthus by long (vs. short to long) rhizomes, its falcate (vs. not falcate) leaves with long acuminate to caudate (vs. shortly acuminate) apex, 5–7(–9) (vs. 7–16) ray florets, and (2–)4–5 (vs. 8–14) disc florets. It is easier to differentiate the new species from the other varieties of A. ageratoides by leaf morphology and number of florets.

Molecular markers, especially nrDNA ITS and ETS, have been used to establish new species in the genus Aster ( Zhang et al. 2015) . Our phylogenetic analysis based on ITS and ETS shows that the two populations of A. oliganthus form a highly supported (PP = 1.00, MP = 99) clade ( Fig. 4 ), and are not nested within the A. ageratoides clade represented here by its four varieties, var. micranthus, var. heterophyllus, var. lasiocladus , and var. ageratoides . As a result, both the phylogenetic and morphological data ( Fig. 4 , Table 2) support its taxonomic status as a new species. Furthermore, the phylogeny ( Fig. 4 ) also shows that A. oliganthus is closest to A. ageratoides . According to the infrageneric classification of Aster by Li et al. (2012), A. oliganthus belongs to A. subg. Aster sect. Ageratoides . Though morphological and karyotypic differentiation between the two populations of A. oliganthus was not found, there was some molecular divergence between them, which indicates that the new species is not newly originated and is evolving. The karyotype parameters of A. oliganthus show low karyotype asymmetry, which is largely similar to those of A. ageratoides ( Li 2002, 2005, Li & Liu 2005). However, A. oliganthus has higher karyotype asymmetry than an A. ageratoides var. micranthus population closely adjacent to the variety’s type locality ( Li & Liu 2005). For example, A. oliganthus has two sm-type chromosomes, an average ratio of 1.27 and a longest/shortest chromosome ratio of 1.84, whereas these values of the A. ageratoides var. micranthus population are 0, 1.21 and 1.52, respectively ( Li & Liu 2005).

The Mt. Hengduanshan region is one of the world’s most important hot spots of biodiversity ( Nie et al. 2002), and A. oliganthus is endemic to its eastern part. Aster oliganthus can be regarded as a characteristic species of the flora of the eastern Mt. Hengduanshan region.

Figures

FIGURE 1. Distribution of Aster oliganthus in the eastern Hengduanshan Mountains region, China.

FIGURE 2. Aster oliganthus. A. Synflorescence (Mt. Erlangshan, Sichuan, China); B. Stigma branches and style (left) and the inside of opened synantherous stamens (right) of a disk floret; C. Disk floret (left) and ray floret (right); D. Habit (Mt. Erlangshan, Sichuan, China); E. A plant with falcate cauline leaves and long rhizomes.

FIGURE 4. Phylogenetic relationships among Aster oliganthus and other sampled Aster species based on nrDNA ITS-ETS sequence data. Bootstrap support values (1,000 replicates) for maximum parsimony (MP≥50 %, right) and Bayesian posterior probabilities (PP≥0.90, left) are provided above the branches. The tree is rooted to Callistephus chinensis and Myriactis nepalensis.

FIGURE 5. Aster oliganthus (from the holotype). A, Habit; B, Apex of a middle cauline leaf; C. A ray floret; D. A disc floret; E–I. Phyllarie (outer surface) in 5 series from the outermost to the inmost; J. Opened synantherous stamens (inside surface) of a disc floret; K. Stigma branches and style of a disc floret. Drawn by Gen-Shen Yin.