The most abundant plant during the first day of my BSBI New Year Plant Hunt 2020 was undoubtedly Winter Heliotrope, Petasites pyrenaicus. It has officially changed its Latin name from Petasites fragrans since my Botanist in the Frost blog last year. Clive Stace officially revised the name in the Fourth Edition of his New Flora of the British Isles. The name was already a query in his Third Edition.
Name Update via Twitter
The name change formed part of an informative Twitter exchange before Christmas between Issy Bryony Hardman, Dan Ryan and Mick Crawley. It resulted from additional, improved Spanish research. The change maintains important consistency with the Flora Gallica and Flora Iberica. Mick Crawley explained in his tweet of 23 December 2019 that the earliest epithet takes precedence even though the genus name is not maintained as the original (basionym):
- Tussilago pyrenaica L. (1758)
- Tussilago fragrans Vill. (1792)
The name hasn’t been a simple matter to resolve. Pyrenaica or pyrenaicus suggests that the plant is native to the Pyrenees. There is doubt as to whether it originated in Europe at all. Stace’s Third Edition mentions North Africa. It won’t be the first time that this confusion has occurred and remains uncorrected in the botanical world.
My own nose would dispute the suggestion of fragrant too. An individual’s sense of smell can be highly personal. Fragrant has to be a pleasant perfume for me. I might accept almond-scented at a stretch. There is a pervasive musty smell to my nose. Perhaps I should put this down to the damp conditions in Somerset this New Year or the frequency of dog-walking in the area? The smell simply doesn’t appeal. The fragrant epithet can go without a fight from me.
Genuine Winter Flower
The majority of the flowers on my New Year Plant Hunt list seem to be members of the Daisy, Asteraceae or Compositae family. The difference with Winter Heliotrope is that we expect it to flower between November and March. Most other plants seem to be late hangers-on this year. To date, I haven’t found any exceptionally early flowering plants.
Winter Heliotrope seems to favour damp streamsides in my neighbourhood. It can also be found on grass verges, rough ground and in waste land habitats.
I tend to think of Winter Heliotrope as having a lopsided inflorescence. Compare the more regular distribution of florets in Butterbur, Petasites hybridus and you may see what I mean. The Butterbur flowers later.
UK plants are all male flowers. There are no female flowers here. The plant does not seem to have any difficulty in spreading vegetatively using its underground rhizome network. The plant can be considered invasive, but it isn’t one of the uncontrollable horrors. Most people appreciate the sight of a rare winter flower.
Poland describes the leaves as regularly sinuate-denticulate with purple hydathodes. This basically means wavy with small teeth at regular intervals around the leaf margins. You can see this in the image below. The leaf shape itself is quite unusual. Poland chooses to include photographs in Plates 12 and 23.
Hand Lens Revelations
Hydathodes are a revelation for which you simply must invest in a hand lens. You don’t need a microscope to see them. Poland illustrates hydathodes using Rosaceae leaves in Plate 22. A hand lens will also open your eyes to red streaks in the stems (petioles). You will end up marvelling at the wide variety of plant hairs that can help in correct plant identification.
Hydathodes are modified pores found on leaves that exude water droplets. These droplets are xylem sap emerging from the plant and should not be confused with dew. This process is called guttation and occurs at night. Transpiration, the process by which water moves through a plant and evaporates, does not usually occur at night as the stomata are closed. When soil moisture is high, root pressure may force some accumulated water to exude from the hydathodes.
I noticed that a number of the Winter Heliotrope leaves had black spots. Research has shown that hydathodes can be a conduit for disease. This may not be of concern in this potentially invasive, naturalised plant, but it does carry implications for food and wine crops.
Plants are fascinating. You start by observing and identifying. You get hooked on looking at tiny characteristics with a hand lens. You notice more and more. The learning never stops. The BSBI New Year Plant Hunt is a good way to get started as a botanist. Winter Heliotrope demonstrates the many different directions in which learning can take you.
Increasing concerns about world food production reveal just how little we understand about plants. Climate change and biodiversity threats make further research critical. Despite Man’s adventures and massive investment in space research, there is still so much to learn about the neglected plants under our feet on this planet.
© Karen Netto (Andrews)
References and Further Reading
Cerutti, Aude et al. (2017): Immunity at Cauliflower Hydathodes Controls Systemic Infection by Xanthomonas campestris pv campestris. Plant Physiology. June 2017, 174 (2) 700-716; DOI: 10.1104/pp.16.01852 Last accessed 3 January 2020.
Chaffey, Nigel (2017): Hooray for the Hydathode! Botany One. July 4 2017. Last accessed 2 January 2020.
Cowing, Bryan (2003-2020): Guttation: Definition and Mechanism. Chapter 9. Lesson 9. A Brief Overview of Guttation Video. Study.com. Last accessed 3 January 2020.
Flora Iberica (2020): Flora Iberica: Vascular Plants of the Iberian Peninsula and Balearic Islands. Last accessed 2 January 2020.
Hardman, Issy Bryony (2019): Missed #wildflowerhour due to an intense family quiz. But pleased to find Winter Heliotrope, Petasites fragrans, growing at Winspit today. Twitter Thread with Dan Ryan and Mick Crawley 22 and 23 December 2019. Last accessed 2 January 2020.
Poland, John & Clement, Eric (2009): The Vegetative Key to the British Flora. Botanical Society of British Isles.
Rand, Martin (2019): Stace 4 Changes. Taxon Lists. pdf. BSBI. Last accessed 3 January 2019
Stace, Clive (2016): New Flora of the British Isles. Third Edition. Cambridge. (83. Petasites Mill. – Butterburs pp.770-771).
Tison, Jean-Marc & De Foucault, Bruno (Ed.) (2014): Flora Gallica. Flore de France. Société botanique de France.
Wildflower Finder (?): Winter Heliotrope, Petasites fragrans. Last accessed 3 January 2019.