Petasites fragrans (Vill.) C. Presl, Winter Heliotrope
Account Summary
Introduced, neophyte, a frequent, naturalised garden escape. European temperate.
1900; Praeger, R.Ll.; Co Fermanagh.
January to October.
Growth form, history of introduction and identification
P. fragrans is a dioecious perennial geophyte that survives overwinter by means of underground dormant buds. A native of N Africa (Libya, Tunisia and Algeria), it was first introduced to English gardens in 1803 from Italy, probably originally as a decorative subject that provided winter flowering interest (Sell & Murrell 2006; Mabberley 2017). It soon escaped garden confines and, in England, was recorded 'in the wild' by at least 1825, in Bayswater, Middlesex (VC 21) (H.J. Killick, in: Strohl et al. 2023). As the common name Winter Heliotrope suggests this species is one of the few that flowers in December and January, the flowering period sometimes extending into March in B & I.
Significant differences displayed by P. fragrans that distinguish it from P. hybridus (Butterbur) are the very sweetly vanilla- or almond-perfumed, pink-mauve or pinkish-white flowers borne in six-20 flowerheads in a loose column inflorescence on stems 10-25 cm tall, and the much smaller leaves (10 cm to only 20 cm in diameter), which are produced simultaneously with the flowers, not after them (Sell & Murrell 2006; Parnell & Curtis 2012).
The question of the perfume is a typical one, for all our noses are different: one person's vanilla is another's almond, and we should never regard the difference between these two scents as taxonomically significant (Genders 1971; Hoare 2000). The flowers attract flies and honey bees that feed on the nectar and pollen provided by the functionally male flowers (Sell & Murrell 2006).
P. fragrans is an exceedingly rampant plant with a rhizome which, depending on soil nutrition and texture, can creep horizontally and burrow deeply underground, spreading up to a metre or more in a year. It can therefore quickly form large and very persistent, clonal patches of dense leaves and was sometimes planted to provide groundcover in demesnes, possibly as additional shelter for chicks of game birds (an association with wealthy landowners that is very obviously demonstrated in Fermanagh).
Another, probably subsequent reason for the introduction and planting of P. fragrans beyond decorative gardens, was as a winter source of nectar and pollen for honey bees (Cat Alien Pl Ir). In common with P. hybridus, which is the only other Petasites species we have in Ireland, all Winter Heliotrope plants are males, which is the sex that provides food for insect visitors (see the current authors P. hybridus account on this website).
Preferred 'wild' habitats
The garden escapes and/or deliberate ex-garden planted clones are most frequently noticed along roadside verges, but they are also found along more or less shaded hedge-, river- and stream-banks, as well as on waste ground, and in places like abandoned quarries where garden rubbish and excess plant material is all too often fly-tipped (Garrard & Streeter 1983).
Fermanagh occurrence
P. fragrans has been recorded in 41 tetrads in Fermanagh, 7.8% of the VC total and, as the tetrad map indicates, it is quite frequent and widely scattered in the lowlands, especially to the N & E of Lough Erne.
Vegetative reproduction and dispersal
All P. fragrans plants throughout B & I are male, making vegetative reproduction obligatory. As is also the case with Japanese Knotweed (Fallopia japonica), any portion of rhizome, however small, provided it bears a node is capable of growth, can serve as a dispersal unit. Both of these alien species manage to spread despite their total lack of seed, rhizome fragments being transported either accidently in soil, or on the wheels of vehicles and, more naturally, floating along waterways after flood spates.
British and Irish occurrence
Once garden confines were broached, P. fragrans soon became thoroughly naturalised in lowland areas throughout B & I, although the species is still much less common and the distribution remains very local in Scotland, where coastal and lowland tendencies become increasingly obvious northwards (Perring & Walters 1962, 1976; Preston et al. 2002; Stohl et al. 2023).
In Ireland, by the mid-19th century, Winter Heliotrope had become well naturalised near the gardens and shrubberies where it had first been introduced, and by the beginning of the 20th century it had been recorded in 34 VCs, reaching all 40 Irish VCs by mid-century (Praeger 1901; Scannell & Synnott 1987; Reynolds 2002). Although these Irish vice-county statistics and the relatively brief timescale of the dispersal might suggest P. fragrans is frequent and widespread throughout the whole island, the New Atlas hectad map indicates that it is much less frequent along the W coast and, rather surprisingly, gaps remain in its occurrence scattered throughout the island.
Despite the severe limitation imposed on its dispersal ability by obligatory vegetative reproduction, the New Atlas survey 1987-1999, indicated that naturalised P. fragrans was still managing to spread in both B & I since the calculated Index of Change during the 40 years between the two BSBI Atlases (1962, 2002) had a positive value as high as + 0.80 (H.J. Killick, in: Preston et al. 2002).
Competitive and colonising ability
The extremely vigorous, far-creeping rhizome of P. fragrans produces relatively large, heavily-shading leaves carried on long stalks. What is probably even more ecologically significant, the foliage is continuously borne, since new leaves are produced before the old ones die off (Salisbury 1964, p. 298). Together these vegetative features must confer a high competitive ability on Winter Heliotrope compared with its neighbours in rough grassy habitats. The established strategy of P. fragrans is categorised as C/CR, meaning it is intermediate between a Competitor and a Competitive Ruderal species (Grime et al. 1988, 2007).
The fact that the species is a native of warmer N African climes must limit the ability of P. fragrans to colonise or to compete quite so rampantly in the cool, mild, wet, oceanic climate of the N & W of the British Isles and in upland areas, but it is not obvious what biological mechanism, or exactly which environmental threshold sets the species limits. The prospect of 'global warming' suggests this alien may become even more prevalent and thus a greater threat to native species in the future.
European and world occurrence
P. fragrans is now reckoned to be native in NW Africa (Stace & Crawley 2015) and is a widespread introduced and naturalised alien in S & W Europe and an occasional alien in C Europe. Functionally female plants have not been recorded anywhere in B & I (Sell & Murrell 2006). As far as anyone is aware, there are no female clones of P. fragrans present anywhere in Europe (Stace & Crawley 2015).
Threats
In Fermanagh, the species is too local and of insufficient frequency in semi-natural vegetation to pose a significant threat, although it would be wise to keep it under review, especially in a more rapidly changing, warming environment.
References
Praeger 1901; Perring, F.H. and Walters, S.M.(eds.) (1962, 1976); Garrard, I. and Streeter, D. (1983); Scannell, M.J.P. and Synnott, D.M. (1987); Preston, C.D., Pearman, D.A. and Dines, T.D. (2002); Salisbury, Sir E. (1964); Reynolds, S.C.P. (2002); Genders, R. (1971); Hoare, A.G. (2000); Parnell & Curtis 2012; Sell & Murrell 2006; Grime et al. 1988, 2007; Stace & Crawley 2015; Stohl et al. 2023; Mabberley 2017.