The genus Senecio L. (Asteraceae Bercht. & J.Presl, Senecioneae Cass.) in Chile was comprehensively revised for the first time by the Argentinian botanist A.L. Cabrera (Cabrera 1949). He recognized 208 species, which organized under an infrageneric classification based on sections and subsections. A few contributions were done afterwards, mainly concerning the description of new species or new records (e.g., Ricardi & Marticorena (1964); Marticorena & Quezada (1977); Moreira-Muñoz & al. (2016); Muñoz-Schick & al. (2016)). Recently, the new catalogue of the Chilean flora recorded 233 Senecio species (Rodríguez & al. 2018). These numbers are nevertheless tentative and a modern taxonomic revision is still lacking.

As part of ongoing studies on the genus Senecio in the Andes (Calvo & Fuentes 2018; Beltrán & Calvo 2019), we here describe a new species from northern Chile on the basis of morphological evidence. It belongs to the group of the caespitose Senecio and keeps morphological affinities with S. algens Wedd., S. altoandinus Cabrera, and S. cremnicola Cabrera. The new species is only known from El Loa Province (Antofagasta, Chile) and thrives in the desertic ‘puna’ ecoregion. Its presence in the neighboring regions of southern Sur Lípez (Potosí, Bolivia) and Jujuy (northwestern Argentina) is likely, and therefore, further field work in these areas is needed in order to improve the knowledge on its variability and distribution area.

This contribution is the result of an intensive revision of herbarium specimens, bibliography, and recent field work carried out in El Loa Province (Antofagasta, Chile). The herbaria visited were CONC and SGO; herbarium acronyms follow Thiers (2019). The main regional treatments consulted for Senecio were Cabrera (1949, 1985) and Freire & al. (2014).

Senecio toconaoensis J.Calvo & A.Moreira sp. nov. Type: Chile, región de Antofagasta, El Loa, Toconao, cordón S de los cerros de La Pacana, 23°9′28″ S, 67°27′56″ W, 4880 m a.s.l., 4–III–2019, J. Calvo 7911 leg. (holo-: SGO; iso-: CONC, MA, Z). Figs. 1 and 2.

LSID: urn:lsid:ipni.org:names:77201991-1

Within the discoid caespitose species with yellowish anthers, style-branches, and corollas, this species differs in its vertical hypogeous stems, fleshy spatulate leaves, entire or with a few incipient teeth, usually with the distal margin undulate or strongly recurved, its solitary capitula subsessile or short-pedunculate, and the long-pilose achenes.

Caespitose perennial herb. Rhizome 1–3 cm long, oblique. Stems 3–8 cm long, hypogeous nearly the whole length, usually with remnants of old leaves, glabrous, plainly white. Leaves spatulate, long-attenuate into a pseudopetiole, glabrous. Leaf lamina 6.5–9 × 3.6–7 mm, rounded at the apex, attenuate at the base, entire or with 3–6 incipient teeth on the margin, usually undulate or strongly recurved at the distal part (in living plants), with the midrib barely conspicuous, fleshy. Capitulum discoid, solitary, terminal, subsessile or short-pedunculate; involucre 7–9 × 6–7 mm. Involucral bracts 13(14), linear-oblong, 5.6–7 × 1.3–2.3 mm, smooth, glabrous. Supplementary bracts 1–2, linear-subulate, 3–4.5 × 0.4–0.8 mm, a third to a half as long as the involucral bracts, glabrous. Disc florets c. 55, 4.7–5.8 × 0.6–0.9 mm, 5-lobed, yellowish with the lobes deep-red. Anthers rounded, yellowish; filament collar balusterform. Style branches truncate with a crown of sweeping hairs, yellowish except for the abaxial surface that is deep-red. Achenes 3.1–3.8 × 0.7–0.8 mm, long-pilose, with trichomes 0.3–0.35 mm long, white; pappus 4.5–5.6 mm long, barbellate, white. Chromosome number: unknown.