Ivy-leaved toadflax
The ivy-leaved toadflax, with its clusters of trailing stems, shiny, kidney-shaped leaves and lilac flowers, is a familiar feature of old, shaded walls across Britain. This plant, which looks so much at home in such man-made habitats, was introduced before the mid seventeenth century as a garden curiosity. The species epithet, muralis ('of a city wall'), reflects the species' habitat outside its native range. Its native home is the southern Alps, the Apennine and Balkan peninsulas and Sicily, where it grows in rocky habitats.
Cymbalaria comprises ten species distributed around the Mediterranean Basin. Although recognised as distinct today, historically it has been included in genera such as Antirrhinum (snapdragons) and Linaria (toadflaxes).
One of the plant's common names, Oxford weed, reflects a belief it first colonised Britain after escaping from Oxford Botanic Garden, where it was recorded growing in 1648. However, in 1640, the English apothecary John Parkinson had already recorded Cymbalaria muralis outside gardens; it was growing 'naturally in divers places' and 'upon the thatched houses in North parts'. The nineteenth-century vogue for using it to adorn walls means today it is naturalised in many temperate regions of the world.
Confusion afflicts another of the plant's common names, bastard (or false) navelwort. Seventeenth-century Italian apothecaries used Cymbalaria muralis as a substitute for navelwort (Umbilicus rupestris), another unrelated species commonly found on walls, in certain medicinal applications.
Cymbalaria has long, spur-like nectaries at the back of the flowers and a bright yellow spot towards the centre of each flower to guide pollinating insects to the pollination rewards. Moreover, Cymbalaria has an unusual means of short-distance seed dispersal that is based on movements of the flower stalk (pedicel). As the flower bud develops, the pedicel grows towards the light. However, once the flower has been pollinated, and seed development has started, the pedicel grows away from the light. The result is that mature seeds are pushed into crevices between rocks, where they will germinate. However, there must also be effective methods for long-distance dispersal since the species has become so widespread since the seventeenth century.
In the late twentieth century, flowering in ivy-leaved toadflax has been used as a biological indicator of climate change. Analysis of a long-term dataset of flowering behaviour of hundreds of flowering plant species in Britain showed on average Cymbalaria muralis flowered 35 days earlier between 1991 and 2000 than it did in the previous four decades.
Further reading
Carnicero P. et al. 2017. Different speciation types meet in a Mediterranean genus: The biogeographic history of Cymbalaria (Plantaginaceae). Taxon 66: 393-407.
Fitter AH and Fitter RSR 2002. Rapid changes in flowering time in British plants. Science 296: 1689-1691.
Junghans, T and Fischer, E 2008. Aspects of dispersal in Cymbalaria muralis (Scrophulariaceae). Botanische Jahrbücher 127: 289-298.
Stephen Harris