Why is this called the Black Widow?

Hi Ajay. I've seen it called a mourning widow before, apparently because the purple of the flowers looks sultry.

Mourning widow the flowers hold themselves down

I think it is to do with the purple colour of the flowers. In Christian symbolism, the colour purple is associated with mourning. This colour asociation extends even beyond Christendom. For instance, purple-coloured cloth is used to signify mourning and death in the Pacific Islands (the recent Royal death in Tonga being a case in point).

Thank you for your answers

It's also called Dusky widow...or dusky cranesbill...it's a geranium.

Geranium phaeum, useful for shady places and seeds about gently. The Mourning Widow.
Jardiniere

Goldfinches like the seeds.

Also supposed to be that the flowers resemble the bonnets worn by widows.