An American mother who married her daughter has been sentenced to two years in prison.

Patricia Ann Spann, 45, pleaded guilty to the felony offence of incest and admitted wedding her biological daughter, Misty Velvet Dawn Spann, 26.

The two married in March 2016 after same-sex marriage became legal in Oklahoma state. Their marriage was annulled last October after a judge concluded the mother had induced her daughter "by fraud to enter the marriage."

Patricia Spann said she thought the marriage was legal because she lost custody of her daughter and two sons years ago and is not listed on their birth certificates.

Investigators found out she was also was married to her biological son in 2008 in Comanche County. The marriage was annulled 15 months later after the son, 18, said it was incestuous. 

No charges resulted from that marriage.