We don't have synonyms for braken yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are broken, brazen and brake.
(n) :
Obsolete form of bracken. [(uncountable, countable) Any of several coarse ferns, of the genus Pteridium, that form dense thickets; often poisonous to livestock.]
(n) :
Obsolete form of bracken. [(uncountable, countable) Any of several coarse ferns, of the genus Pteridium, that form dense thickets; often poisonous to livestock.]