Manu Smriti describes marriage of eight types - 

(1) Braahm - In this father offers his daughter to the boy.

(2) Daiv

(3) Aarsh

(4) Praajaapatya

(5) Aasur

(6) Gaandharv

(7) Raakshas

(8) Paishaach

Among all these the first one is considered the best.

Putrikaa Dharm 
In this type of marriage, parents of the girl take their daughter's first son as their own son, even if the parents have their own son(s). Manu married his daughter Aakooti to Ruchi Prajaapati according to this Dharm and thus had her son as his own son, although he had already had his own two sons.