I wouldn't freeze seeds.

Ipomoea aquatica

http://plants.ifas.ufl.edu/misc/pdfs/SP ... 067%29.pdf

This species is on the FL DACS Prohibited Aquatic Plant List – 5B-64.011. According to Florida Statute 369.25, “No person shall import, transport, cultivate, collect, sell, or possess any noxious aquatic plant listed on the prohibited aquatic plant list established by the department without a permit issued by the department.” See 5B-64.011 for more information.

This species is also on the Federal Noxious Weed List – (7 CFR 360). No person may move a Federal noxious weed into or through the United States, or interstate, without a federal permit. See 7 CFR 360 for more information.