A new method of measuring differences between dicotyledonous families – the ‘evolutionary distance’ (ED) – is proposed. This aims to complement Sporne's ‘advancement index’ of correlated characters. The EDs of families from the Chloranthaceae and Magnoliaceae are used to predict which families may have been in existence the longest. As the Hamamelidaceae and Saxifragaceae appear to be most ancient by this method, the EDs from the Hamamelidaceae have been calculated to test this. From these EDs, other ancient or core families can be proposed. Most notable are the Sphaerosepalaceae, Buxaceae, Canellaceae, Cunoniaceae, Euphorbiaceae, Rosaceae and Tetracentraceae. By considering the ED and advancement index together, the Quiinaceae, Dipentodontaceae and Trochodendraceae can be added to this list.