I found this on a site called Goddess School. I cannot find any info on Fluxwort. It may be an old name for something else. Hedgeberry appears to be any red or dark berry grown on a hedge.Do not ingest Mistletoe Berries, they can cause convulsions.In her mysterious cauldron, according to ancient Celtic legend, Cerridwen prepared a potion of enlightenment for her son that consisted of the yellow flowers of the cowslip, fluxwort, hedgeberry, vervain, the berries of the mistletoe (a plant sacred to the Druids), and the foam of the ocean. It was warmed by the breath of nine maidens, and required brewing for a year and a day.ETA: I did finally find something on flux wort. It is in the same family as Milkweed. Also called Pleurisy Root.
I can see why substitutions where used. Foam of the ocean is not easy to come by. Distilledwater would work.
We get sea foam here all the time. It happens when a storm comes in and waves crash against the rocks. The wind catches it and sends it all over the place. It can be really slippery when its on the roads. You would think it would be kinda pretty(think sea foam green paint) but its not. Dirty looking and smells terrible... Wonder if I could bottle it with date/time gathered and location and ship it... LOL