'mixed-leafed' is a compound formed from 'mixed' + 'leafed'. 'mixed' comes ultimately from Latin 'miscēre' (via Old French and Middle English) where the root meant 'to mix'; 'leafed' derives from English noun 'leaf' (Old English 'lēaf').

'miscēre' passed into Old French (e.g. 'mescler'), then into Middle English as verbs meaning 'to mix' (e.g. 'mixen'), becoming modern English 'mix' and its past participle 'mixed'. 'Leaf' comes from Old English 'lēaf', through Middle English to modern English 'leaf', and the adjectival suffix '-ed' formed compounds like 'leafed'. These elements combined in modern English to form descriptive compounds such as 'mixed-leafed'.

The components originally referred to the actions/objects 'to mix' and 'leaf', and their combined compound has retained the literal descriptive meaning 'having mixed leaves' with little semantic shift.