For yesterday’s blog post about bees and pesticides I used a picture, taken last week, of a bumble bee visiting some Pulmonaria rubra 'Redstart' that I have for ground cover under some trees at the bottom of the garden.
It made me think about the Pulmonaria genus because Pulmonaria angustifolia 'Blue Ensign' was present in the Alnwick Garden Poison Garden.
The task for the ‘garden historian’, as she describes herself, who provided the original plant list for the Poison Garden was a difficult one. The need was to provide a display of poisonous plants whilst trying to ensure that there was something to see throughout the year. There was also the further complication that, due to a misunderstanding on one side or the other, a number of plants were included that were really antidotes or herbal remedies. I’ve written before about the challenge of finding poison stories to attach to some of those plants.
Looking back at the manual I prepared for the guides, I see that the Pulmonaria has the shortest entry of any plant. This just says that it contains hepatatoxic pyrrolizidine alkaloids (PAs). In theory, that would mean that ingestion would lead to liver failure as PAs are the toxins found in Jacobaea vulgaris, common ragwort, formerly Senecio jacobaea.
I now regret that when I prepared that guide I didn’t make any note of where I had found the information I used. Obviously, for plants like Atropa belladonna, deadly nightshade, there is no doubt about its toxicity and there are plenty of references, easily found but, with some of the more questionable plants, I do wish I could go back to the source I used to see more detail.
Pulmonaria rubra 'Redstart'
Since I don’t have that shortcut available I’ve had to go through my library and see if I could find any reference. The four or five books I usually turn to had nothing to say about Pulmonaria and John Gerard’s refers only to its medicinal uses. I’ll return to those, shortly. To complete my checks I turned to what is, almost certainly, the strangest publication in my collection. This is a bound version of a print U.S. Department of Agriculture, Agricultural Research Service, Technical Bulletin No. 1264.
It is called ‘Alkaloid-bearing Plants and Their Contained Alkaloids’ and was published in 1961. It is a long schedule, organised by family giving all the substances then known to be present in plants. There are a great many unknowns i.e. where alkaloids have been identified as being present but they have not been fully characterised. There are also many, many alkaloids that are named for the plant. The well-known ones are aconitine and aconine from Aconitum napellus, monkshood, but just opening the book at random, Mucuna pruriens contains mucunine and four other alkaloids with names beginning ‘muca’.
It illustrates how much there was still to be learnt about botany, fifty years ago, because I think we can be certain that many of these individually named alkaloids are structurally identical, or, at the very least, extremely similar. One reason that I don't refer to it that often is that much more has been discovered since 1961. So, it is really just a curiosity and, of course, no-one is ever going to produce another document like it because that sort of information is best kept electronically.
Technical Bulletin No. 1264 lists 3,671 plants but none of them is a member of the Pulmonaria genus.
Finally, I found a reference online saying that Pulmonaria falls within the Boraginaceae family and many of the genera within that family contain PAs so the assumption is that Pulmonaria will also have PAs present. But it is only an assumption.
Still, if the Pulmonaria’s claim to be poisonous is rather limited it was a useful plant to have in the Poison Garden. Not only did the Pulmonaria angustifolia 'Blue Ensign' produce some stunning colour early in the spring when there was little else to see, its common name, lungwort, derived from its use to treat chest problems, which use was based on the appearance of the leaves, was a good example of the flaws in the Doctrine of Signatures.