Fungus — Alien — What is a life form?

This is a relatively old story,, but I was reminded of it recently while working on conceptualized alien beings.  If we don’t truly understand or relate to Terran species as in a two thousand acre fungus and probably most of the deep sea trench residing critters, how can we hope to understand or even recognize a truly alien life form?

http://www.scientificamerican.com/article/strange-but-true-largest-organism-is-fungus/

This is relatively old (2007) but still valid conceptually.  Worth another look I think.