American cudweeds (Gamochaeta; Gnaphalium s.l., Asteraceae) in Belgium and the Netherlands

In recent years several species of American cudweeds (Gamochaeta; Gnaphalium s.l.) have increasingly been recorded in Belgium and the Netherlands, especially (but not exclusively) in urban habitats. Since these species are naturalizing – at least one even on a relatively large scale – assessing their genuine identity is necessary. Three species are eventually accepted: G. coarctata (previously erroneously ascribed to G. purpurea), G. pensylvanica and G. subfalcata (surprisingly often overlooked for the native species Gnaphalium sylvaticum). In this paper all are copiously depicted and characters useful for their separation are discussed. A key for their identification is also presented, as are details about their distribution and habitat preferences in Belgium and the Netherlands. The naturalized populations reported in this paper are probably the northernmost known worldwide. Finally, the genome size was assessed for several accessions. It turned out that genome size does hardly allow to separate G. pensylvanica and G. subfalcata.