Lifeforms As Criterion for Species Delimitation: Are Aristida Adscensionis and A. Coerulescens (aristidoideae, Poaceae) Two Species?

The distinction of the perennial Aristida coerulescens from the annual A. adscensionis and its taxonomic treatment has been subject of long discussions. We here include accessions from the Mediterranean and Macaronesia for molecular phylogenetic analyses and conducted a morphometric analysis. A lineage of A. adscensionis, A. coerulescens and A. effusa is well supported in phylogenetic trees. Moreover, a group of Mediterranean, Macaronesia and Arabian A. coerulescens and A. adscensionis is revealed where both taxa are intermingled. A morphological analysis of traditionally used spikelet characters did not indicate a clear separation of both taxa. We therefore conclude that A. coerulescens should best be treated as synonym of A. adscensionis. The differential character of annual and perennial life forms seems to be plastic in this taxon indicating rapid shifts between these two strategies.