Characters for Tadaaki's family name were "千種" and are read as "chi-gusa" ("gusa" having the same pronunciation as "kusa" which means "grass" in Japanese); their title "Sanboku-Isso" was coined after their names as the character "木" (boku) is also read as "ki" which means "tree," leading to "Sanboku-Isso" which literally means "three trees and one grass."
千種は「チグサ」と4人の姓、あるいは呼び名からとられている。