'simple-flowered' originates from Modern English, formed by compounding the adjective 'simple' and the past participle 'flowered'. 'simple' ultimately comes from Latin 'simplex', where 'simplex' meant 'single', and 'flower' comes via Old English/Old French from Latin 'flos' (genitive 'floris'), meaning 'flower'.

'simple-flowered' developed in Modern English as a descriptive compound combining 'simple' (from Old French 'simple', from Latin 'simplex') and 'flowered' (from English 'flower', from Old English/Old French 'flor', from Latin 'flos, floris'), and has been used in botanical descriptions to mean 'bearing single flowers'.

Initially the elements meant 'single' ('simple') and 'flower' ('flos'); the compound 'simple-flowered' has consistently been used to mean 'having single (not double) flowers' and has retained that specific botanical sense.