Over de volledigheid van de tweede inventarisatieronde van het IVON (1950-1980)

The second series of inventories by the IVON (Institute for the Investigation of the Vegetation in the Netherlands) is evaluated as to its completeness. A minor number of hour-squares appears to be insufficiently investigated; one of the main gaps is found in the (until recently rather inaccessible) Flevoland polders. Notably incomplete are the distribution data of some species flowering in spring and disappearing before summer (fig. 4). Finally, in the IVON investigation lists several 'aggregate taxa' were only split up into subspecies or microspecies in the 1970 's; distribution data from areas investigated before that time are rather scarce. A list is given of 42 'ubiquitous' species, which are to be expected in every 'normal' hour-square. Referring to the meaning of the abbreviation IVON, the author stresses the need for co-operation between floristic workers and vegetation investigators.