This info is too late for this season, but in general, lands that are run by the USDA forestry service have the most permissible collection laws, in my experience. You still may need a permit depending on what you want to collect, but would have to contact your regional center. However, I'm not sure of your state or county laws, so collection permits may be feasible on state lands, too.
Some plants native to Maryland that may be available in stores include: lizard's tail (Saururus cernuus), cardinal flower (Lobelia cardinalis), creeping rush (Juncus repens), Elodea canadensis (IF legal), Cabomba caroliniana (again, may have legal issues), mermaid weed (Proserpinaca palustris), Eleocharis acicularis, and (if properly labeled) jungle val (Vallisineria Americana), and (if properly labeled) dwarf sag (Sagittaria subulata)
Edited by Fmajalis, 22 December 2018 - 12:46 AM.