'haplostemonous' originates from New Latin (botanical), ultimately from Greek: the element 'haplo-' meant 'single' and 'stemon' meant 'stamen'.

'haplostemonous' was formed in botanical New Latin from Greek components ('haplo-' + 'stemon' + adjectival suffix '-ous') and entered English technical botanical usage with essentially the same form.

Initially it described the morphological condition 'having a single whorl of stamens' and this specific technical meaning has been retained in modern botanical usage.