Septimus Weasley is the father of Arthur Weasley.
Cedrella Black's marriage to Septimus Weasley caused her to be "blasted" from the Black Family Tree (see BFT and my notes).
Weasley="In Britain and Ireland the weasel has a bad reputation as an unfortunate, even malevolent, animal. However, since childhood I have had a great fondness for the Family Mustelidae; not so much malignant as maligned, in my opinion." (JKR) This genus includes weasels, stoats, polecats, ferrets, mink, wolverines, badgers, skunks, otters, and others.