Chromosomal speciation processes gain increasing attention in plant systematics and evolution, and new approaches revealed a high diversity in chromosome numbers even within recognized taxa. Reliable counts linked to known accessions are thus needed yet often hardly available. We present a new online database for chromosome counts and ploidy estimates of the flora of Germany with a detailed documentation of the examined material, and its sampling locality. The chromosome database builds upon a relational database and includes standardized taxon identification, study date, georeferenced locality and additional collection as well as publication details from which the karyological information was extracted. In order to reach the best compatibility with other botanical publications of the study region, taxonomic concepts and nomenclature follow the “Rothmaler”, a widely accepted field flora of vascular plants in Germany. Our online database is available at http://chromosomes.senckenberg.de. The site consists of the main page with project information, a search tool, an interactive map display, a contact and a data submission form. The zoomable map shows the localities of the search result, allows to refine the geographic search as well as to select individual data points.