Type:— BRAZIL. “Province of Goyas: dry upland sandy campos between Arrayas and San Domingos”, May 1841, G. Gardner 4259 (K 895327, photo!, lectotype designated here, isolectotype K 895326, photo!).

There are 14 specimens labelled as ‘Gardner 4259’. Most of them are bearing “ isotype ” labels, but none was pointed out as a holotype or selected as a lectotype, which indicates that they are all syntypes. The only specimen dated 1840, which is the date indicated in the protologue, is NY 232634, but it’s extremely depleted. The other ones present “1837”, “1841”, the periods “1836–1841” and “1837–1841”, or have no date on the label. So the criterion ‘date’ had to be pushed aside in selecting the lectotype. Then we decided for a specimen in good condition, with more information on the label and probably hermaphrodite (according to the personal communication of Dr. Sue Frisby from K). Therefore the specimen K 895327, which dates from 1841, was chosen as the lectotype.

Additional specimens examined (remaining syntypes): — BRAZIL. S.l., s.d., G. Gardner 4259 (GH 11434, photo!); s.l., s.d., G. Gardner 4259 (RB photo!); Goiás, s.l., s.d., G. Gardner 4259 (E, photo!); ibidem, s.d., G. Gardner 4259 (GH 11435, photo!); ibidem, s.d., G. Gardner 4259 (MNHN-P 2140862, photo!); ibidem, s.d., G. Gardner 4259 (MNHNP 2140863, photo!); ibidem, s.d., G. Gardner 4259 (MNHN-P 2140864, photo!); ibidem, s.d., G. Gardner 4259 (NY 232633!); ibidem, 1836–1841, G. Gardner 4259 (NY 232632!); ibidem, 1837–1841, G. Gardner 4259 (BR, photo!); Goiás: between Arrayas and San Domingos, May 1837, G. Gardner 4259 (BM, photo!); ibidem, May 1840, G. Gardner 4259 (NY 232634!).

In Brazil, the species occurs in Goiás, Minas Gerais, Mato Grosso and São Paulo, and its occurrence in Rio Grande do Sul was mentioned with doubt by some researchers as Malme (1931) and Petenatti & Ariza-Espinar (1997). Also, as cited by Zuloaga et al. (2016), the species occurs in Argentina (Provinces of Misiones and Entre Rios). Here we confirm the occurrence of this taxon in the coastal region of Rio Grande do Sul.

This species is close to Porophyllum obscurum (Sprengel 1826: 38) Candolle (1836: 651); however, P. angustissimum is more branched and has narrower (filiform) and more numerous leaves when compared to P. obscurum, whose leaves are linear to narrowly lanceolate. Gardner (1848) described P. angustissimum comparing it to P. lineare Candolle (1836: 649), currently a synonym of P. obscurum, and citing as differences “its numerous leaves, involucral scales a third longer, its very much narrower, shorter achaenia and narrower leaves” among other features.

In Brazil Porophyllum obscurum occurs in Rio Grande do Sul (further to the west), Paraná, São Paulo, Minas Gerais, Goiás, Distrito Federal, Mato Grosso, Mato Grosso do Sul and Bahia (Nakajima 2016). Also it was found in Argentina, Paraguai and Uruguai (Zuloaga et al. 2016). It has therefore a wider distribution when compared to that of P. angustissimum, showing some overlapping in Midwest and Southeast of Brazil.