These are some various posts on plants in crayfish tanks:
'Anachris and camobea (sp on both) are favorite snacks so they look pretty, but are gone fast. I have java ferns right now (red leafed sword) and they nibble but don''t just tear them down. I am buying about 10 every 2 months or so, but I like a heavily planted aquarium too.
'Mine tend to eat most of the plants I put in, but I found one called Cabomba that they just like to climb in. I have 3 clumps that have been in my tank for quite a while now and seems to be growing, though I don''t see any roots.
'you can let anachris float. my elvis loves chewing on wisteria, but that is not a floating plant. i also like java fern, which he doesnt tear up too much. java ferns dont need to be planted in gravel. just fixed on a rock or something, i even let them float sometimes and they grow like crazy in all my tanks