What Plant is This?

[Cloud]

I agree it does look a bit like a Datura but the flowers don't seem quite right somehow.

I'd go with Datura. They have quite a variation in phenotype and lots of genetic hybrids, like many weeds. It should soon be getting little seed pods that look like chestnuts.

[Brother of four]

Yes, it appears to be a Datura "type" called Jimson Weed or ranchers call it Loco Weed. Active ingredients are Belladonna alkaloids, atropine, scopolamine. You can smoke it for the hallucinations but one leafs potency is different from the next so overdoses are common. Former medicinal uses were for asthma, it being an anti-spasmodic.