It seems that he was genetically related to Tadamune OBU whose home ground was Obu no sho like Suesada's, so it is sometimes said that he was of Seiwa-Genji Yoshitada lineage, which was founded by Tadamune's father, MINAMOTO no Yoshitada.
同じ飯富庄を本拠地とした飯富忠宗との血縁関係があったのではないかということから、忠宗の父、源義忠を流祖とする清和源氏義忠流といわれることもある