Senecio festucoides (Senecioneae, Compositae), a new species from northern Chile

Abstract Senecio festucoides is described from northern Chile. The new species is morphologically similar to the discoid caespitose Andean species and belongs to the subgroup displaying yellow corollas and yellowish anthers and style branches. It is characterized by a weak, not self-supporting stem, narrowly linear leaves, long pedunculate capitula with (17–)21 involucral bracts, and minutely papillose achenes. Among other characters, the color of the corollas, anthers, and style branches and the number of involucral bracts differentiate it from S. scorzonerifolius, which is the morphologically closest species. The new species thrives in the desertic Puna ecoregion and grows amongst tufts of Festuca chrysophylla (Poaceae). Detailed pictures of living plants are provided, as well as a distribution map and a dichotomous key to the discoid caespitose Senecio species from northern Chile.

In Chile, the first comprehensive revision of the genus recognized 208 species and treated 11 taxa as dubious (Cabrera 1949). Some of the species accepted by Cabrera are currently placed in new or resurrected genera as a result of efforts to redefine the generic delimitation of Senecio (Nordenstam et al. 2009). This is the case for S. yegua (Colla) Cabrera and S. cymosus J.Rémy, which are widely accepted as being part of the genus Acrisione B.Nord. Likewise, traditionally accepted genera such as Culcitium Bonpl. and Robinsonia DC. are currently treated within Senecio in order to move towards a monophyletic generic concept of this genus (Pelser et al. 2007;Pelser et al. 2010). Further contributions aimed at improving the understanding of the Chilean species mainly concerned nomenclatural adjustments (Marticorena and Quezada 1974;Soldano 1998) and the addition of new records and species (Cabrera 1954(Cabrera , 1955Ricardi and Marticorena 1964;Quezada 1974, 1978;Moreira-Muñoz et al. 2016;Muñoz-Schick et al. 2016;Rodríguez et al. 2018;Calvo and Moreira-Muñoz 2019;. The species described in Chile after the taxonomic revision by Cabrera (1949) are detailed, and taxonomically updated if needed, in Table 1.
The checklist of the Chilean flora records 233 Senecio species (Rodríguez et al. 2018), however, this is an estimated number that will require adjusting following further taxonomic revision of the group. Here, we describe a new species from northern Chile as a result of field work carried out during 2019 and 2020. It is similar to discoid caespitose species and belongs to the subgroup displaying yellow corollas and yellowish anthers and style branches (see ). The morphologically closest species is S. scorzonerifolius Meyen & Walp. A detailed taxonomic discussion, a distribution map, and pictures of living plants are provided, as well as a dichotomous key to the discoid caespitose Senecio species from northern Chile.
Distribution and habitat. Chile (Antofagasta, Tarapacá). Considering the proximity of both populations to the Bolivian territory and the presence of similar environments across the border, its presence in this latter country is likely. It thrives in exposed grassy slopes and plains of the desertic Puna ecoregion, between elevations of 4325-4550 m (Fig. 3).
Senecio festucoides grows amongst tufts of Festuca chrysophylla Phil. (Poaceae) [= F. orthophylla Pilg. according to Ospina et al. (2013)] (Fig. 1F); indeed, the tufts provide  support for S. festucoides stems, which are not self-supporting. If the new species is not in flower, it is difficult to detect because its leaves are easily confused with those of Festuca (Fig. 1C, D). The following species were observed in the same habitat: Astragalus minimus Vogel ( Etymology. The epithet festucoides refers to the conspicuous resemblance of the leaves to those of Festuca chrysophylla, amongst which the new species grows. Conservation status. Thus far, the new species is only known from two locations and has an extent of occurrence of ca. 2000 km 2 . This would fit the category Endangered (EN) according to the B1a criteria (IUCN 2012). However, it is preliminarily assigned to the category Near Threatened (NT) considering that further data on distribution and population dynamics are essential to firmly establish that the species is facing a very high risk of extinction in the wild.
Discussion. Senecio festucoides shows morphological affinities with the sympatric species S. scorzonerifolius (Fig. 3), which is known from southern Peru, western Bolivia, northwestern Argentina, and northern Chile. Although these species have a similar appearance, they belong to different subgroups within the discoid caespitose Andean Senecio, i.e. the new species is a member of the subgroup displaying yellow corollas and yellowish anthers and style branches whereas S. scorzonerifolius belongs to the subgroup with white corollas and blackish anthers and style branches (Fig. 2B). They also differ in leaf indumentum (glabrous in S. festucoides vs. densely to barely arachnoid, rarely almost glabrous in S. scorzonerifolius), peduncle bract type (linear bracts up to 6 mm long in S. festucoides vs. leaf-like bracts up to 30 mm long that gradually decrease in size upwards in S. scorzonerifolius; see Fig. 2A), involucral bract number and length ((17-)21, 10-11 mm in S. festucoides vs. (9)13-15, 8-9 mm in S. scorzonerifolius), supplementary bract length (3.9-6 mm, a third as long as the involucral bracts in S. festucoides vs. 6-8 mm, a half to two thirds as long as the involucral bracts in S. scorzonerifolius; see Fig. 2A), and achene indumentum (minutely papillose in S. festucoides vs. papillose in S. festucoides). Moreover, S. festucoides has longer stems and does not develop crowded tufts as S. scorzonerifolius usually does (Fig. 2C, D). In living plants, their leaf color is also different (yellowish green in S. festucoides vs. dark green in S. scorzonerifolius; see Fig. 2C).
The leaf shape of the new species might lead any botanist to confuse it with S. bolivarianus Cuatrec., a species endemic to Peru known from Ancash to Moquegua (Beltrán and Roque 2015). They can be readily differentiated by the abaxial leaf surface (densely silky-villous except for the midrib in S. bolivarianus vs. glabrous in S. festucoides), leaf margin (revolute in S. bolivarianus vs. flat in S. festucoides), leaf base (broadened into a sheath-like base that bears long silky trichomes in S. bolivarianus vs. uniform in width and glabrous in S. festucoides), and number of supplementary bracts (12-16 in S. bolivarianus vs. (3-)5-8 in S. festucoides). Moreover, S. bolivarianus has linear to narrowly lanceolate leaves rather than narrowly linear as in S. festucoides.
It should be noted that S. festucoides is characterized by its narrowly linear, entire leaves but we also observed a few specimens displaying both entire and distantly dentate leaves. Such leaf dimorphism is usual in other related species such as S. digitatus Phil. ) and S. scorzonerifolius (Cabrera 1985 ; Fig. 2D).

Key to the discoid caespitose Senecio species from northern Chile
The dwarf shrubs developing erect stems are excluded (e.g. Senecio puchei Phil., S. socompae Cabrera, S. trifurcifolius Hieron.). Senecio festucoides is not a strictly caespitose species but it is included in this informal group on the basis of the taxonomic placement of its morphologically similar species. As pointed out in , the color of the corollas, anthers, and style branches has taxonomic value within this group and is readily noticeable in living plants. However, a careful study of these characters on dried specimens is required to avoid misidentifications.