they definatly look like phragmite australis, swim once went on an adventure trying to get some
, well swim did found it , but the truth is extracting the spice from it, is kind of a "nut cracker", cuz your really not shore if you gonna get anything if anything at all, also there is the danger of "gramine"/or other dangerous kemikalz innit, innit?
i reckon if it was that easy to get it from phragmites , everyone on this forum should be concentrating in getting it rather than buying "mimosa" from growers.
i hope you can find a safe way of extracting it , and please enligth us with your new found knowledge
maybe you can makes us all free from expenses in the future
good luck