The name louseworts share really isn’t deserved.
They aren’t ‘lousy’, by any means, or at least not in appearance and in the modern sense of the word; indeed, Flowers of India (which has become my Bible for these biweekly posts) describes this individual – the rattle lousewort – as “beautiful”.
So why lousewort? It’s an old wives’ tale, as it appears: apparently, should you ingest these flowers – though I don’t know why you would – lice will appear in your stock. Hence, lousewort.
Lousewort, therefore, here is applied in the sense of the creature rather than the adjective. A saving grace, perhaps, for such a lovely, delicate flower.
But it’s immediately doomed again: louseworts belong, unfortunately, to the broomrape family. And as it happens they’re parasitic anyways, so perhaps the name is deserved.