Gutierrezia mendocina ( Asteraceae , Astereae ) , a new South American species

Gutierrezia mendocina (AsterAceAe, AstereAe), A new south AmericAn species.— A taxonomic revision of the South American species of Gutierrezia has revealed a new species from Argentina, characterised by its stems with the base prostrate and rooting, turbinate heads and white ray florets. This species, found in the Department of Tunuyán of Mendoza Province (Argentina), is described and illustrated and a key to differentiate it from allied species is given.


INTRODUCTION
Gutierrezia Lag. is a New World xerophytic genus of the tribe Asteraeae, subtribe Solidagininae (Funk et al., 2009).It is present in North America, where 18 species are recognised (Nesom, 2006), it does not occur in Central America, but reappears in southern South America with ca. 13 species, of which one was recognised in Bolivia and has been collected in La Paz and Santa Cruz Provinces (Solbrig, 1966); and finally six in Chile where they inhabit in the regions Metropolitana, I, II, II, IV, V, VI, XI and XII (Zuloaga et al., 2008).In Argentina, according to Zuloaga et al. (2008), the genus Gutierrezia grows from Jujuy to Territorio Nacional de Tierra del Fuego and is represented by eight species, six of which are endemic to this country .
The South American species were monographed by Solbrig (1966), who recognized 11 species, of which six inhabit Argentina with five being endemic.
More recently, Sancho & Ariza Espinar (2003) published a floristic survey of Argentina where eight species are described, of which six are endemic.Recently, Sancho (2013) cited two species for the province of San Juan.However, since Solbrig (1966) there has not been a further taxonomic revision of the genus Gutierrezia.
During the revision of the genus Gutierrezia we found one herbarium specimen collected by O. Boelcke in 1963 in western Argentina, near Mendoza city (Boelcke 10082, BAA).It was quite different from other South American species by its stems prostrate and rooting at the base, the shape of the leaves (the inferior elliptic-spathulate and the superior linear-elliptic), the turbinate involucre, and longer lamina of the ray florets, which are white in colour.A member of the team (F.Ratto) went to the original site of collection in the Department of Tunuyán (Mendoza Province) and found two populations of this species, all in a small area near Puesto de Gendarmería Alférez Portinari.

Etymology:
The specific epithet refers to the Argentine province where it has been collected.Phenology: Gutierrezia mendocina has been collected in flower in January; it was found in full bloom.
Distribution and habitat: Gutierrezia mendocina has only been collected in the Department of Tunuyán in Mendoza Province (Argentina).This species inhabits the transition of phytogeographical province of the Monte belonging to the Domain Chaco and phytogeographical province of Patagonia of the Domain "Andino-Patagónico" (Cabrera, 1971).This area, whose characteristic vegetation is a xerophytic steppe, has a relatively low mean annual precipitation, from 80 to 270 mm.Mean annual temperature varies from 13°C to 17°C (Cabrera, 1971).Gutierrezia mendocina grows on rocky hillsides (Figs. 3 and 4), orientated towards the north, at about 2100 m in scattered populations and is associated with Larrea Cav., Cassia L., Chuquiraga Juss., Grindelia Willd., Prosopis L. and Junellia Moldenke.Due to the scattered populations all having been found in a small area near Puesto de Gendarmería Alférez Portinari, this species could be considered endangered.However, this is subject to further exploration in the area.
Taxonomic position: Gutierrezia mendocina is akin to G. spathulata (Phil.)Kurtz also from Mendoza province and G. taltalensis Phil.from the north of Chile due to its prostrate habit and the head grouped in corymbiform cymes and it also shares white ray florets with G. taltalensis.However, the new species can be distinguished from G. spathulata and G. taltalensis by its stems rooting at nodes and dimorphic leaves.

Figure 3 .
Figure 3. General view of type locality of Gutierrezia mendocina.In the background, the Cordillera de los Andes.