It turns out that California is already on the case, and banned taxifolia and several other species of caulerpa back in 2001:
CALIFORNIA CODES
FISH AND GAME CODE
SECTION 2300
2300. (a) No person shall sell, possess, import, transport, transfer, release alive in the state, or give away without consideration the salt water algae of the Caulerpa species: taxifolia, cupressoides, mexicana, sertulariodes, floridana, ashmeadii, racemosa, verticillata, and scapelliformis.
(b) Notwithstanding subdivision (a), a person may possess, for bona fide scientific research, as determined by the department, upon authorization by the department, the salt water algae of the Caulerpa species: taxifolia, cupressoides, mexicana, sertulariodes, floridana, ashmeadii, racemosa, verticillata, and scapelliformis.
(c) In addition to any other penalty provided by law, any person who violates this section is subject to a civil penalty of not less than five hundred dollars ($500) and not more than ten thousand dollars ($10,000) for each violation.
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I wonder how many dealers are aware that it's illegal to sell these varieties to Californians?