Improving Checklists of Alien Plants with Digitised Herbarium Collections: The Example of D.R. Congo (Africa)

Abstract The Democratic Republic of the Congo (D.R. Congo) represents a striking gap of knowledge on alien plant species. In this paper, we use digitised herbarium collections to assemble a checklist of alien plant species in D.R. Congo and to examine patterns in the alien flora. The new checklist comprises 426 alien species i.e., 182 (42.5%) casuals, 244 (57.5%) naturalised of which 80 (19% of aliens) are invasive. Discrepancies with previous databases are discussed. For many species in previous databases, we failed to find evidence for occurrence outside cultivation. A total of 158 taxa were not included in previous lists, 44 of which are new to D.R. Congo. Considering the size of the country and its rich native flora, the alien flora of D.R. Congo does not appear to be species rich. The alien flora is particularly rich in Fabaceae (15%) and in annual species (36%). America is by far the most important source continent (65%) and the proportion of annuals of American origin is particularly large among the most widespread species. Invasive success is discussed in terms of residence time. The very low number of new species records after 1960 is most likely accounted for by decreasing sampling effort. The results illustrate how herbarium collections can be used to critically revise existing checklists of alien species in tropical Africa. Field work is urgently needed to improve coverage of recent introductions and to monitor the status of alien species, especially in protected areas and around botanic gardens.