20 ECU Carl Von Linne

The ECU — European Currency Unit — was never legal tender in Sweden, yet Sveriges Riksbank issued collector pieces denominated in it throughout the 1990s as a quiet gesture toward potential EU monetary integration. Sweden joined the EU in January 1995, the same year this piece was struck, but would later vote against adopting the euro in a 2003 referendum.

Linnaeus remains the choice here for obvious reasons: his 1753 Species Plantarum and the binomial nomenclature system he formalized are still the operative framework for botanical classification worldwide.