Morphology and anatomy of leaves in the succulent <i>Duseniella patagonica</i> (Barnadesioideae, Asteraceae) in relation to arid environments and saline soils of the Monte and Patagonia of Argentina

Abstract Barnadesioideae, consisting of 87 species distributed in mesic and xeric regions of South America, are the sister group of the remaining Asteraceae. Molecular phylogenetic hypotheses have revealed a consistent topology of relationships among the 10 currently recognized genera. Schlechtendalia is sister to two clades: (i) Dasyphyllum, Barnadesia, Huarpea, Archidasyphyllum, Arnaldoa, and Fulcaldea, and (ii) Chuquiraga, Doniophyton, and Duseniella. Chuquiraga consists of 22 species that are divided into two monophyletic sections, sect. Chuquiraga and sect. Acanthophylla. The former includes 13 species adapted to the Andean zone ranging from Chile and Argentina to Colombia. Sect. Acanthophylla encompasses nine species distributed primarily in arid zones in the southern Andes (Chile, SW Bolivia, and Argentina) and down into the Monte and Patagonia of Argentina. Doniophyton has two species with D. weddellii restricted to dry, higher elevations of the southern Andes between Chile and Argentina, and D. anomalum confined to the Monte and Patagonia, where the monospecific Duseniella (D. patagonica) is also located. Southern Andean and Patagonian taxa have morphological and anatomical adaptations for survival in arid environments. Chuquiraga sect. Acanthophylla has adapted by maintaining a shrubby habit with acicular leaves, whereas Doniophyton, although consisting of annual species, also has narrow, drought-resistant leaves. Duseniella patagonica is the most morphologically divergent species within the group, being annual and succulent, and the only succulent species within Barnadesioideae. Duseniella is distributed in arid and saline habitats in playas with seasonal rainfall. The leaves are succulent, amphistomatic, oriented vertically, with both surfaces sparsely pubescent or glabrous. The mesophyll is isobilateral with two or perhaps three palisade layers. Spongy mesophyll consists of large aquiferous cells that contain chloroplasts and have wavy contours. The vascular bundles are numerous from the base of the leaf, coalescing in a reticulate pattern at the apex. To meet the challenges of survival in environments of extreme water stress, it is proposed that, based on morphological and anatomical data, Duseniella may have a flexible C3/crassulacean acid metabolism (CAM) photosynthetic system, being C3 during its rapid growth during the spring rains followed by a transition to CAM in the extremely parched summer months.