There is a parentElementArrayFinder attribute available on an ElementFinder object which, from I understand, may return a parent element of the current:
var myElement = $(".myclass");
var parentElement = myElement.parentElementArrayFinder;
It is, though, not documented as a part of Protractor's public API. Is parentElementArrayFinder a reliable and stable method to locate a parent element and would always return the same element as myElement.element(by.xpath(".."))?