New to science: Petasites japonicus x P. fragrans

Source: Hoare, Arthur. “New to science: Petasites japonicus x P. fragrans.” Sussex Botanical Recording Society Newsletter, no. 82 (May 2016).


Janette and I decided to take a walk round Borde Hill Garden near Haywards Heath: unfortunately we found the garden closed, but there is a farm track which is also a public footpath running alongside the garden, so rather than return home we chose to take a walk along the track. We had only covered a couple of 100 metres when serendipitously I saw a plant that was a mystery to me. My first thoughts were of Petasites but it did not look like any species I knew. There was a large patch so I collected enough material to take and study once I got home. Still not able to get a positive identification, I sent a note to Eric Clement about the find along with a voucher specimen and as much detail about the plants as I could. Eric suggested the possibility of the female Petasites fragrans but not having a herbarium specimen to compare it with he advised me to contact Dr Fred Rumsey at the Natural History Museum where they may have a herbarium specimen. He also mentioned that Stace 3rd ed. states that the female Petasites fragrans is not known in Britain and that if the specimen was what he thought it was, then this would be a most important find.

Dr Rumsey was contacted by email giving him all the details that I had given to Eric Clement to see if he was prepared to accept the challenge and if possible confirm the identity of this Petasites. Thankfully, he readily agreed. This necessitated a return visit to the site to gather fresh material. Since my original find just over a week had passed and the plants were not in a pristine state. However, I managed to collect fresh material that I hoped would be acceptable as a voucher specimen. Arriving at the garden and finding it was open; I entered to inquire at the reception if there was anyone I could speak to about the plants in the garden and in particular my mystery plant. I was kindly directed to Andy Stevens the head gardener. When asked about the plants he said he knew them only as Petasites and that there were a number of patches scattered about the garden. He also said that they were a problem plant, which didn’t surprise me. He was not sure of the actual species and unaware of the female plant of P. fragrans; nor did he know how or when the plants arrived in the garden. One can only assume it was an accidental introduction but going by the size of the patches, and having an idea of the rate of spread of P. fragrans, these colonies must be at least 50 years old. I was in no doubt that the source of this alien invasion was in the garden. Although a frequent visitor to the garden I had not noticed these plants before; but then when walking around a large garden I suppose it is easy to overlook the less showy specimens when confronted by the splendid displays of the gaudy horticultural show-offs.

The collected plants were prepared and voucher specimens pressed and sent to the Natural History Museum.  Then only few days later the reply I was hoping for arrived. Dr Fred Rumsey confirmed my mystery plant as the female Petasites fragrans and that my voucher specimen is now housed in the Museum’s herbarium.

A note was submitted to BSBI News and shortly after publication I was surprised to receive an email from Prof. Clive Stace expressing his interest in my account and wondering if it would be possible to get hold of some growing material.  It was agreed that living material was available and a suitable amount was collected and despatched to Prof. Stace so that he could proceed in carrying out his studies.  He indicated that he would like to visit the site, and I arranged a visit with Paul Harmes, Mike Shaw, David Streeter and Clive Stace in attendance.

It soon became apparent that what we were looking at was something quite special, with certain characters of other Petasites species present in the plants so this could not possibly be the female P. fragrans. This meeting closed with many more questions to be answered before a conclusion could be reached. Subsequently, Prof. Stace requested DNA samples to be collected and then sent away for molecular analysis.  The results of the analysis proved beyond all doubt that the ‘Borde Hill Butterbur’ is in fact a hybrid between Petasites japonicus and P. fragrans – a plant that is new to science.


See also: Dawn Nelson. “Arthur’s Butterbur.” Sussex Botanical Recording Society, 9 March 2017 <>.