Before today, I’ve never seen a frond of Pteridium esculentum (Austral bracken) that was fertile - to the point that I stopped even looking long ago. Today, I happened to notice a fertile frond drooping over the path, and as I went on, some areas seemed to have more than half of the fronds near the path being fertile. In other areas, it was less common but they were generally still around. The only reason I can come up with for this is the recent (current…) fires in the national park, but a quick Google search turned up nothing connecting fertility in the species with fire. Has anyone else ever noticed such a (potential) connection? Or are there other causes that I’m not thinking of?
1 Like
In Britain you are advised not to walk through bracken at certain times of year because of the carcinogenic spores (Pteridium aquilinum). I have been cutting bracken for eight years and have never found a frond with spores on, and I think I would have noticed. The literature (can’t remember which paper) says P. aquilinum is more likely to produce spores following a fire. A fire passed through where I work in 2018 but I still didn’t see any spores here.
2 Likes
I think bracken can spread (sporulate) with any disturbance, including fire
There’s lots of bracken in the Long Island Pine Barrens, specifically Eagle Fern (Pteridium aquilinum latiusculum). Many hiking trails pass through areas where hikers are likely to brush against the ferns as they pass, or where they might breath in spores on windy days. The woods in my back yard are an example. I have noticed fertile fronds at times, but have not paid close attention to their abundance. How serious is the carcinogenic issue?
1 Like
Here (Wales, UK) it is a major invasive species. I can’t remember the figure but I think 10-15% of Wales is covered by bracken. The majority of the spread is vegetative, and that gets a boost after fire because competing vegetation is removed and there is a pulse of fertiliser from the ash. Apparently the rhizomes will creep some distance underground but not put up fronds until there has been a fire so it suddenly appears over a new area.
2 Likes
I don’t know how serious is the risk from spores. Certainly eating bracken is a bad idea, though it is practised in some countries. I have a suspicion that risk-averse H&S department in Countryside Council for Wales noted bracken is carcinogenic and bracken produces wind-blown spores, so decided to tell CCW staff not to work in or down wind of bracken in mid-summer so that H&S can’t be blamed if any staff claim working in bracken made them ill. I did ask them how far into the Irish Sea we needed to go in order not to be downwind of bracken but they didn’t reply.
Some notes from publications:
Pamukcu et al. 1978. Carcinogenic and mutagenic activities of milk from cows fed bracken fern (Pteridium aquilinum). Cancer Research, 38: 1556-1560.
Around a quarter of rats fed on milk from cows fed on bracken developed cancers of small intestine, kidney or bladder within 117 weeks, compared to zero in the control group.
Vetter, J. 2009. A biological hazard of our age: bracken fern [Pteridium aquilinum (L.) Kuhn.] - a review. Acta Veterinaria Hungarica, 57: 183-196.
Not read in detail. Suggests toxins from bracken can enter the water supply.
Cody, W.J., & Crompton, C.W. 1975. The biology of Canadian weeds. 15. Pteridium aquilinum (L.) Kuhn. Canadian Journal of Plant Science, 55: 1059-1072.
(p. 1061) Bracken poisoning is synonymous with chronic and acute enzootic haematuria in cattle, otherwise known as redwater disease. Bracken poisoning is difficult to detect and diagnose because of its delayed effects. It is equally toxic when fresh or dry.
Rogers, S. 1985. Bracken. Nature in Devon, no. 6: 31-49.
Individual cows may develop a craving for bracken but in general problems in cattle only arise in years when the spring growth of grass is delayed by cold or dry weather and the succulent emerging fronds may be eaten in quantity (on Dartmoor). Sheep are generally more tolerant than cattle and the disease known as bright blindness does not seem to be a problem in the south west.
Recouso et al. 2003. Clastogenic effect of bracken fern (Pteridium aquilinus v. arachnoideum) diet in peripheral lymphocytes of human consumers: preliminary data. Veterinary and Comparative Oncology, 1: 22-29.
Prolonged consumers of bracken (humans) had increased levels of chromosomal abnormalities in their lymphocytes.
Marrs, R.H. 2000. Is there life after bracken? Lecture given at Bangor University, 16 November 2000.
There are correlations between bracken and human cancers in North Wales. Rhizomes are eaten in Japan and China after blanching to remove toxins and those countries have the highest world incidence of human gut cancers, but this could be caused by other unusual aspects of their diet. Bracken is rarely eaten by people in Wales. The toxic secondary compounds are ptaquilosides and shikimic acid. These are not found in Welsh drinking water. Spores are rarely produced. So the cause of the Welsh correlation is not known. The effects on animal health are clearer:
Horse: bracken staggers
Pig: rhizome poisoning
Cattle: bone marrow toxin and tumours
Sheep: bone marrow toxin, tumours, blindness
Rats: in lab, causes thiamine deficiency and early death unless given vitamin B1.
4 Likes
John, you’re touching on a very interesting topic — the connection between plants and cancer — and I have a lot to say about this topic, but I won’t, in order to stay focused on the original topic of bracken spores. Which you did mention in your post.
It’s an exceedingly common plant which since centuries is covering vast areas of Europe, and yet it’s not associated with any increase in cancer rates. That should tell you how dangerous the spores or any leachate into the ground water are for humans.
Cows and pigs will however eat it when there’s no other food available, and be poisoned. Interestingly it’s apparently addictive - animals which get poisoned by it want to eat more.
1 Like
My question may have been what got us off-topic. However, the responses were very interesting, so thank you!
It would be great to read what you and others have to offer about that topic. If you start a new discussion about that, many of us would find it interesting.