Maternal relatives

Thanks for your question! The maintenance of family ties, or at least its duty, is irrespective of whether it is the paternal relatives or maternal relatives. I know of no source that differentiates the two in that respect. They are simply differentiated in terms of inheritance (Ref. Ahkaam). 

As for a hadith about maternal aunts, I don't readily know if there is a hadith to that respect, but in terms of the judgements, they are considered as mothers. Imam al-Haadi (as) said in his Ahkaam:

Similarly, Allah prohibited marrying paternal and maternal aunts because they are counted as parents and mothers. 

So, in terms of the prohibition of marrying them and their offspring, maternal aunts are considered as mothers. However, in terms of anything else, such as obedience similar to the mother, I know of no such relationship.

And Allah knows best!

IRS 

Thank you for asking for clarification! I mistakenly added 'and their offspring'. The Qur'an, Sunnah and consensus permit marriage with the children of uncles and aunts. It is simply the marriage to aunts and uncles that is forbidden.