Phytolith analysis of the main species of Distichlis sp. (Chloridoideae: Poaceae) distributed in South America

Abstract

The Saltgrasses are pioneer plants in the early stages of succession in saline soils and constitute particular zonal communities of low species variability. Phytolith assemblage analysis of these species allows a community type to be characterized that consists mainly of species with well-defined environmental adaptations, which are significant because of their paleoecological importance. The aim of the present study is to characterize phytolith assemblages of Distichlis species in South America, emphasizing their leaf morphotypes. Four Distichlis species, mainly of South American distribution, and four chloridoids species from different clades of the subfamily (Lycurus, Eragrostis, Muhlenbergia and Sporobolus) were selected for this study. The phytoliths were obtained following Labouriau's calcination technique. Quantitative analysis of the morphotype abundance in the phytolith assemblages studied allowed the three main groups to be distinguished, with the common presence of multicellular phytoliths with long, short, bulliform and subepidermal silicified cells, as well as unicellular phytoliths, such as short narrow saddle, prickles and hairs, polyhedral and long elongate types. Conversely, the exclusive presence of horned towers, short truncated cones, circular/ovoid, papillae trichome, silicified microhairs, and isolated and articulated irregular epidermal cell phytoliths in Monanthochloinae clade species distinguishes them from the Muhlenbergiinae clade species with square/rectangular and subrectangular saddles and acute dumbbells. Eragrostis and Sporobolus species have shown some particular morphotypes (such as hairs with cushions, long truncate cones, dumbbell and dumbbell/saddle). The results not only allowed us to identify the Distichlis species, but also to distinguish them from other grasses, including those in their subfamily; and represent a potential tool to identified halophytes environments outside New World saltgrasses.