Senecio tridentatus DC., Prodr., DC. & Prodr.

Calvo, Joel & Granda, Arturo, 2022, On the taxonomic identity of five Senecio species (Compositae) described by Candolle on material collected by Haenke during the Malaspina Expedition, Candollea 77 (2), pp. 145-158 : 156

5. Senecio tridentatus DC., Prodr. 6: 424. 1838, syn. nov.

Lectotypus (designated here): ARGENTINA /URUGUAY: sine loco, s.d., Haenke s.n. ( PRC [ PRC453191 ] image!; isolecto-: P [ P01816571 ] image!, PR-616648 image!) .

= Senecio crassiflorus (Poir.) DC., Prodr. 6: 412. 1838. Cineraria crassiflora Poir., Encycl., Suppl. 2(1): 267. 1811. Holotypus: ARGENTINA. Prov. Buenos Aires: Buenos Aires, s.d., Commerson s.n. (P-LA [P00342427] image!).

Notes. – CANDOLLE (1838) indicated “Peruviâ” as the provenance of the original material of Senecio tridentatus . Any information in this regard lacks in the three type specimens we studied. DILLON & HENSOLD (1993) stated that the presence of this species in Peru remained to be confirmed and VISION & DILLON (1996) recorded it with no information about its distribution. The study of the type material reveals that S. tridentatus is identical to S. crassiflorus , a very distinctive species frequent in the sandy shore habitats of SE Brazil, Uruguay, and E Argentina (F REIRE et al., 2014). It is a rhizomatous perennial herb characterized by having whitish-lanate indumentum covering most parts of the plant, leaves oblanceolate, attenuate at base, dentate at upper half to tridentate at apex (sometimes entire or almost so), capitula radiate, large, arranged in lax corymbiform synflorescences or solitary, composed of 21–25 involucral bracts, and achenes c. 5 mm long, pubescent.

As in the case of Senecio adscendens (see above), the species S. crassiflorus is not rare in the region of Río de la Plata (ARECHAVALETA, 1906; CABRERA , 1963; F REIRE et al., 2014). Then, Haenke most probably collected it during the three months that he remained between Montevideo and Buenos Aires or when he left the latter city westward to Mendoza, Santiago, and Valparaíso. Mislabeling in Haenke’s specimens is well documented, and therefore, the name S. tridentatus is included in the synonymy of S. crassiflorus .

The type material of Cineraria crassiflora Poir. is known from a single specimen in P-LA collected by Philibert Commerson (1727 – 1773) in Buenos Aires. Another collection by Commerson made in November 1767 shows the locality Montevideo; in disagreement with F REIRE et al. (2014), we prefer do not consider it as original material because of the mismatch in the locality.