Homostylium Nees

Chen, Xinyu & Fu, Zhixi, 2025, Resurrection of the genus Homostylium Nees for the former Aster ser. Albescentes Y. Ling (Astereae, Asteraceae), with an updated generic synopsis, PhytoKeys 259, pp. 27-66 : 27-66

Homostylium Nees , Del. Sem. Hort. Bot. Vratisl. 3. 1844, emend. Z. X. Fu

= Aster ser. Albescentes Y. Ling , Fl. Reipubl. Popularis Sin. 74: 357. 1985.

= Sinosidus G. L. Nesom , Phytoneuron 2020-64: 12. 2020.

Type.

Homostylium cabulicum (Lindl.) Nees.

Description.

Perennial shrubs. Stems erect to spreading, profusely branched. Leaves alternate, leathery, subleathery, herbaceous, or chartaceous, basal leaves withering at flowering, middle cauline leaves ovate, lanceolate to linear; margins entire to remotely apiculate, serrulate, or coarsely serrate, revolute or flat; adaxially glabrous or sparsely appressed pubescent; abaxially closely gray- to white-tomentose or sometimes glabrous, sometimes glandular beneath the tomentum with sessile, resinous glands. Capitula pedunculate, solitary or in corymbose or paniculate-corymbose inflorescences at branch tips. Involucres campanulate, cylindrical or obconic, 5–9 mm wide (pressed). Phyllaries in 3–5 - seriate, imbricate, strongly graduate, keeled, oblong, ovate, ovate-lanceolate to lanceolate, glabrous to nearly glabrous, or sparsely short pubescence, tomentum; margins membranaceous or scarious, sometimes ciliate, abaxially herbaceous or sometimes leathery. Florets heteromorphic, numerous, outer ray florets 1 - seriate, pistillate, white, pink, or violet-blue, lamina 3 - lobed, glabrous, glabrescent, sparsely filiform-pilose or puberulent; central disc florets numerous, bisexual, yellow, tubes glabrous or sparsely to moderately pilosulous basally or apically, limb 5 - lobed, lobes equal or unequal, glabrous or sparsely puberulent, sometimes glandular. Anthers linear, base obtuse, subauriculate, or caudate, apical appendage lanceolate. Styles glabrous or distally papillate; bifid in disc florets, branches linear, abaxially glabrous or sparsely papillate, adaxially two stigmatic lines of densely papillate cells from base to appendages; apical sterile appendages triangular or lanceolate, papillate; filiform in ray florets, not bifid. Receptacles flat or convex to conic, alveolate, sometimes lacerate, epaleate, glabrous. Pappus persistent, white, straw-colored, or reddish-brown, with numerous subequal strigose bristles, outer layer extremely short strigose bristles. Achenes white, straw-colored, tan, or reddish brown, compressed, fusiform, cylindrical, oblong, or obovoid, strigillose, (3 -) 5–8 - ribbed, pilose, pubescent, or glandular-pubescent.

Distribution.

6 of 7 species endemic to SW China. Only Homostylium albescens distributed widely in SW China and the Himalayan region ( Nepal, Bhutan, India, Myanmar, Bangladesh, and Kashmir) (Fig. 1 ).

Habitat.

Alpine and subalpine forests and shrubs, aridly hot river valleys, rock cliffs, and streambanks.

Phenology.

Flowering June to October. Fruiting August to November.

Etymology.

It is derived from the Greek “ Homo - ”, meaning “ same ”, and “ - styl - ”, meaning “ pillar / style ”, combined with the Latin “ - ium ”, a common neuter genus suffix. The genus name probably refers to the uniform style in the florets of Homostylium species.

Notes.

Among the seven species names in Aster ser. Albescentes , the earliest published was Amphirhapis albescens DC. in 1836 by A. P. de Candolle, with no type cited. Jeffrey (1982) later typified the genus Amphirhapis DC. with Amphirhapis heterotricha DC. However , this species was subsequently treated as a synonym of Duhaldea eupatorioides (DC.) Steetz in the genus Duhaldea DC. of the tribe Inuleae ( Anderberg 1991) . It made the name Amphirhapis no longer applicable to accommodate Aster ser. Albescentes . The second earliest name was Homostylium Nees published in 1844 by Mr. C. G. D. Nees von Esenbeck. Homostylium was originally a monotypic genus including only Homostylium cabulicum (Lindl.) Nees. This species is currently treated as a synonym for Aster albescens . The genus is characterized by its shrubby habit, dentate leaves, corymbose inflorescences, cylindrical involucres, imbricately arranged lanceolate-acuminate phyllaries, 1 - seriate pistillate pale violet ray florets, bisexual disc florets with 5 - lobed limb, and compressed, pubescent, cuneate achenes, as described in its original protologue (https://seedlists.naturalis.nl/content/homostylium-cabulicum-nees). The original morphological characters of Homostylium are generally consistent with those of Aster ser. Albescentes . However, no type specimen information was provided in the protologue.

In the Flora Reipublicae Popularis Sinicae ( Ling et al. 1985), we found that Homostylium cabulicum was cited as a synonym under the name Aster albescens . However, Mr. Rong Ling marked this synonym as “ nom. nud.? ”, suggesting it might be a nomen nudum with uncertainty. This was probably due to him not having seen the original literature. After reviewing the original literature published in 1844, we found the monotypic genus Homostylium had a detailed description of its characteristics and essential traits, confirming it as validly published and not a nomen nudum. Notably, the name Homostylium has not also been used for other taxa. Therefore, we adopted the validly published genus name Homostylium with nomenclatural priority to accommodate 7 species of Aster ser. Albescentes , in accordance with Articles 11, 41.2, and 42.1 of International Code of Nomenclature for Algae, Fungi, and Plants (Shenzhen Code) ( Turland et al. 2018). Initially, Homostylium was published as applicable only to Aster albescens . However, to include the remaining six species ( A. lavandulifolius , A. argyropholis , A. fulgidulus , A. motuoensis , A. hypoleucus , and A. polius ) and its varieties, the genus concept is broadened.

Figures

Figure 1. Distribution of the genus Homostylium Nees. China is centrally located on the map.