Ixeris is a genus of annual and perennial herbs in the family Asteraceae (order Asterales), native to East and South Asia. The genus belongs to subtribe Crepidinae within the vast daisy family and is sometimes called the Asian hawk's-beard group.
Plants are typically rosulate, with stems that are ± erect; some species also produce long creeping stems with erect flowering branches. The leaves vary from undivided and spatulate to pinnately or palmately lobed. Flower heads (capitula) are arranged in corymbiform synflorescences and bear (12–)15–25(–40) florets per head. The involucre is cylindric to narrowly campanulate, with glabrous phyllaries arranged in several series; inner phyllaries are usually 8, linear-lanceolate, and roughly equal in length. Florets are ligulate and yellow, occasionally whitish or purplish. The achenes are brown, ± fusiform with 10 prominent, wing-like ribs, tapering into a filiform or slender beak; the pappus consists of white, scabrid bristles.
About eight species are currently recognized, distributed across East and South Asia, with six species recorded in China. The genus was published by Cassini in 1822 (based on his 1821 subgenus of Taraxacum), and its modern circumscription was established by Pak and Kawano (1992) through carpological and karyological investigations. The basic chromosome number is x = 8.
The boundaries of Ixeris have shifted considerably with advances in molecular systematics. Numerous species once assigned here have been transferred to related genera including Crepidiastrum, Ixeridium, Paraixeris, Youngia, Lactuca, and Paraprenanthes, reflecting a recircumscription of subtribe Crepidinae supported by phylogenetic analyses. The former monotypic genus Chorisis (accommodating I. repens) is now included within Ixeris.
Etymology
The genus name Ixeris derives from the basionym Taraxacum subgenus Ixeris coined by Henri Cassini in 1821, elevated to genus rank by Cassini himself in 1822. The Chinese common name 苦荬菜属 (ku mai cai shu) means roughly "bitter lettuce genus," reflecting the plant's membership in the chicory tribe and the characteristically bitter latex shared by many relatives in Asteraceae.
Distribution
Ixeris is distributed across East and South Asia. About eight species are recognized, with six occurring in China; the genus also extends to Japan and Korea. Species such as I. repens occupy coastal and strand habitats, while others such as I. chinensis and I. polycephala are widespread across a range of disturbed and open habitats throughout the region.
Taxonomy Notes
The circumscription of Ixeris has been substantially revised. Pak and Kawano's 1992 treatment (based on carpological and karyological data) is the framework adopted in Flora of China and has since been corroborated by molecular phylogenetic analyses of subtribe Crepidinae. Under this concept, the former genus Chorisis (containing I. repens) is synonymized into Ixeris, and the basic chromosome number is established as x = 8. Prior to molecular work, many species now placed in Crepidiastrum, Ixeridium, Paraixeris, Youngia, Lactuca, Agoseris, Paraprenanthes, and Sonchella were included in Ixeris in the broad sense.
