Alien Legacy of the Building Boom in Ireland

Winter Heliotrope, Petasites fragrans

This unseasonably warm winter has seen the blossoming of crocuses, daffodils and snowdrops in gardens throughout Ireland a lot earlier than usual. It makes a change from the previous two years, when this blog noted that daffodils had yet to bloom by March. One plant that will flower earlier than all of these regardless of the weather is the Winter heliotrope (Petasites fragrans). A native of the Mediterranian, it was seemingly introduced from Naples to gardens in France at the end of the 18^th century by Dominique Villars (1). Its flowers have a sweet, vanilla perfume, emerging from January to March (2) and it soon became a favourite. Populations produce either male or female flowers, with some florets of the opposite sex intermixed in the flower spikes (sub-dioecious) (3). It was introduced to England in 1806 (where, as in Ireland, only male flowers are found), where it was favoured as an ornamental in gardens and made its way to Ireland by about 1835 (4). Soon becoming naturalised, P. fragrans is now established and common throughout Ireland, and has proved to be , according to botantist Tony O'Mahony, the “greastest, single, alien plant threat to wildlife habitats in Ireland” (5).

Winter Heliotrope, Petasites fragrans, entirely covering a riverside verge

Growth and spread is by underground rhizomes and colonisation of new ground is swift. The round leaves remain on the plant all year, creating a blanket coverage of habitats and giving it a competitive advantage over most native shrubs (4). It is especially quick to colonise newly disturbed ground, something the building boom of the 2000s in Ireland provided in abundance. Embankments of new roads, riverbanks and banks throughout the country are now dominated by P. fragrans. Yet while it has been identified as a real and present threat to Irish native plant species (6), so far no legislative action has been taken to tackle the problem (4).

References:

1. Hogg and Johnson, 1864. The Wildflowers of Great Britain
2. Phillips, 1977. Wildflowers of Britain p. 26 
3. Toman, 1983. Folia Geobotanica 18 pp. 433-437  
4. O'Mahony, 2009. Wildflowers of Cork City and County pp. 348-350
5.  Killick, 2002. New Atlas of the British and Irish Flora 
6. Dolan, 2004. The Effects of Human Transport on Ecosystems: Cars and Planes, Boats and Trains pp. 15-62