Ask Mr. Smarty Plants

First of all, I'm sorry, but we no longer accept photos of plants for identification.  We were overwhelmed with photos and don't have enough staff and volunteers to do the research to identify the plants in the photos.  As you can read on our Plant Identification page:

"We would love to spend all day identifying native plants for you folks! However, we already spend all day (and most of the night) answering your native plant questions. Luckily, there are some excellent forums available to help you identify those mysterious unknowns."

However, I am going to suggest two possibilities for your plant from your description as being a "flowy bambooish" plant.  One is Ipomopsis rubra (Standing cypress) and the other is Baccharis neglecta (False willow).  Both look rather like bamboo before they bloom.  You didn't mention whether it had bloomed or not.  The standing cypress is a biennial and doesn't bloom the first year it comes up; so, if that is what it is, you certainly don't want to pull it up before you get to see its spectacular bloom.  It is certainly a nectar source for butterflies and hummingbirds, but I couldn't find any mention of it being a larval host for butterflies.  The other plant, Baccharis neglecta (false willow), grows rapidly and will bloom the first year.  I found one species of moth, Condica charada, whose larvae feed on Baccharis neglecta and it does serve as a nectar source for butterflies.

If you still have the label for your butterfly plant seed mix, you might check the different species that are listed on it (if they did list them) and search in our Native Plant Database to see the what the species look like.  If they are given as botanical names, use those for searching.

If neither of these is your plant, then your best bet is to visit our Plant Identification page where you will find links to several plant identification forums that accept photos for identification.