Biological Flora author (and editor) Anthony Davy introduces a fascinating coastal species that offers many more ecological insights than one might imagine.
This account of the Sea Campion (Silene uniflora) is the latest contribution to the long-running Biological Flora of Britain and Ireland series. The article itself has a long history: unusually, the authors include the Editor of the series since 2004 (Tony Davy), his late predecessor (Arthur Willis) and Alan Baker, whose PhD study of the species enjoys its half-centenary this year.
The showy, white flowers of Sea Campion grace cliffs, dunes and shingle banks around the Atlantic and Baltic coasts of Europe all summer long, where they are conspicuous enough to attract people’s attention, not least that of a British Poet Laureate.
“The seagulls plane and circle out of sight
Below this thirsty, thrift-encrusted height,
The veined sea-campion buds burst into white”
Cornish Cliffs by John Betjeman
Silene uniflora has a remarkable breeding system. Some plants have only hermaphrodite flowers, others just female-only flowers (i.e. lacking stamens), and yet others both types of flower on the same plant. They are particularly attractive to long-tongued Hymenoptera and night-flying moths, who are the prime pollinators. Less well-endowed insects rob the nectar by piercing the side of the inflated calyx to reach the base of the corolla.
Hermaphrodite (left) and female-only (right) flowers of Sea Campion. Photos: A.J. Davy
Nevertheless, Sea Campion’s interactions with its pollinating benefactors are ambiguous. Some pollinating moths may oviposit in the flowers and resulting caterpillars subsequently consume the capsules and seeds, whereas pollinating insects commonly also transmit the spores of castrating fungal diseases, so-called ‘anther smuts’ because of the sooty appearance of their spore masses (mainly of the genus Microbotryum). S. uniflora and its close congeners have been widely used as model systems in studies of these plant venereal diseases.
Although less common than on the coast, populations also occur on mountains and heavy-metal mine waste tips, where the plants show considerable tolerance to heavy metals in the soil. Again, it has featured as a model species, ever since the pioneering studies of Alan Baker, for physiological and molecular studies of the evolution of zinc-tolerant populations. In contrast, plants of coastal populations are halophytic, showing substantial tolerance to salt and low water potential in their environments; we report that seed germination can occur at salinities of up to 200 mM NaCl (about half that of seawater) in controlled conditions.
An historical claim to fame for S. uniflora has been its role in long-term experiments that were seminal to the development of ‘experimental taxonomy’ in the early-to-mid 20th century. Its close relationship with the more widespread, ruderal S. vulgaris was investigated by examining diverse populations from all over Europe and subjecting them to crossing experiments. A key feature involved transplanting them to a common garden, with a range of different soils, to distinguish the contributions of genotypic and phenotypic (plastic) effects to trait variation. The British Ecological Society was instrumental to this by sponsoring, establishing and maintaining transplant experiments at their gardens at Potterne in Wiltshire between 1928 and 1938. This approach might be thought of as a precursor to the Biological Flora series itself, founded in 1941. Much of the work on Campions is summarised in a monograph by E.M. Marsden-Jones and W.B. Turrill published by The Ray Society in 1957.
Details of these varied aspects of Sea Campion ecology can be found in the Biological Flora account.
Tony Davy and Alan Baker express their warm appreciation of Prof. Arthur Willis (1922-2006) as mentor and friend.