Answer: I searched and searched and managed to come up with a database of native plants for the Texas Gulf Coast. You'll have to go through the over 700 entries to determine which are considered weeds (most are classified as wildflowers), but at least it's a step in the right direction. You might also try contacting a local branch of the Native Plant Society. Someone there may be able to supply you with a list. Here's the database: http://tpid.tpwd.state.tx.us/species_commonname.asp
Hope it's helpful!
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