Hello everyone.

Is there any method for determine native countries of a species of plant?

I am asking because I scanned at Nymphaea rubra Roxb. ex Andrews on 2 websites:

The first website said N. rubra native to Assam, Bangladesh, Cambodia, India, Jawa, Malaya, Myanmar, Philippines, Thailand, Vietnam while the second one does not mention the native countries.

Do I need to check herbarium specimens of the species and find those first collected ones? Or I need to do something else?

Thanks in advance.