'unusual-flowered' is a modern English compound formed from 'unusual' and 'flowered'. 'Unusual' comes from the negative prefix 'un-' + 'usual' (from Latin 'usus' meaning 'use'), and 'flowered' derives from 'flower' (Old English/Old French influence from Latin 'flos, flor-' meaning 'flower').

'unusual' entered English via Middle English/Old French from Latin roots related to 'usus'; 'flowered' is formed from the noun 'flower' (from Old English/Middle English 'flor/flower', ultimately from Latin 'flos') with the adjectival/past-participial suffix '-ed'. The compound itself is a recent descriptive formation in Modern English, combining the adjective 'unusual' with the participial adjective 'flowered'.

Initially the components meant 'not customary' ('unusual') and 'having flowers' ('flowered'); combined, they now denote 'having flowers that are uncommon or atypical' with no substantial shift beyond the compositional sense.