Shtuki-One who does not know the identity of his father:<a href="#_ftn1" name="_ftnref1">[1]</a>
Mother: A person who is Halachically defined as a Shtuki, which is that he does not know the identity of his father even though he knows the identity of his mother, is [nonetheless] liable for hitting and cursing his mother. [Accordingly, it is understood that such a son is equally obligated to honor his mother even though he does not know the identity of his father.]
Acclaimed father: A person who is Halachically defined as a Shtuki is not liable for hitting and cursing his father. This applies even if the mother claims a certain man to be his father, nonetheless, she cannot cause him to get punished due to her word.
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<a href="#_ftnref1" name="_ftn1">[1]</a> Michaber 241:7; Rambam Mamrim 5:9

Shulchan Aruch HaRav | Shtuki-One who does not know the identity of his father:

Shtuki-One who does not know the identity of his father:[1] Mother: A person who is Halachically defined as a Shtuki, which is that he does not know the identity of his father even though he knows the identity of his mother, is liable for hitting and cursing his mother.