Bioaccumulation is the gradual accumulation of substances in an organism, in this case; alum. There are a few plants that are bio-accumulators of alum. For example, the fallen leaves of the Symplocos tree, tea leaves can contain very high concentrations of aluminum (up to 5,000 mg/kg in old leaves), and a few ferns.
Clubmosses (Lycopodiopsida) are also rich in aluminium, there are around 400 species of this seedless vascular plant that is actually not a moss but an evergreen fern, and the one that we use now for natural dyeing on the website is organic Lycopodium clavatum and it is mindfully harvested from Romania.
Clubmoss has a long history of use in traditional herbal medicine, clubmoss teas and poultices can be used to treat urinary tract problems, diarrhea, relieve headaches and skin ailments. I have no personal experience with this, and do not recommend trying this without consulting a physician.
As a mordant, it looks like Clubmosses were known and used in ancient times in Northern Europe (Anglo Saxon and Viking cultures) and the Americas regularly in combination with locally grown natural dyes. I certainly think it has a place to try and work with this material as an alternative to regular alum but care is warranted; in countries such as the Netherlands and Belgium, Clubmoss is protected by law and you may not harvest it for your own use.
I prepared different sets of fabrics with clubmoss and one without clubmoss
Set 1: 100% WOF (17 grams) of Clubmoss
Set 2: no clubmoss
I warmed the set with the mordant materials in plenty of water to 40ºC for about two hours, and then let it soak for another two days. I have 3 liter beaker glass beakers for this. The Clubmoss mordanted samples turned a faint green. Next time I would probably brew some kind of tea from it and sieve the plant bits before adding the fibers, cleaning the bits and pieces was annoying and clogged my sink. My new heater stirrers are amazing and I am so happy I made the purchase!
Samples with walnut hulls, heated to 80ºC; left mordanted with clubmoss, bringing out more of the yellows in some of the samples, right no mordant at all.
More testing will follow for different dyes, but this was a nice beginning.