The large bellflower, Wahlenbergia linifolia, is currently St Helena’s most threatened flowering plant. It is an inhabitant of the cloud forest which still clings-on to the very summits of the island’s central ridge. In the 19th Century, large bellflowers were a familiar sight amongst the tree ferns and cabbage trees, thriving in the damp, mossy conditions around their bases and on the trunks. However, only a few plants now remain, scattered between High Peak and the Depot. Invasive weeds have claimed much of the suitable habitat and the remaining plants are restricted to a few isolated peaty cliffs which are prone to land slips.
Recently, a more insidious threat has emerged: the species is believed to hybridise with a more widespread relative, the small bellflower, This problem has pushed the large bellflower to the edge of extinction. It is probable that many of the individuals, other than a core population of 20-30 plants, are no longer genetically pure. The small bellflower is generally a species of lower altitudes but a little overlap may always have thrown-up a few hybrids. However, now that the large bellflower is so acutely threatened, pollen carried to the sites is much more likely to come from the more abundant sister species.
In order to save the last relicts of the large bellflower, we urgently need to identify which of the surviving plants are pure. This is not necessarily straight forward as some hybrids may have crossed back with pure parents, providing offspring which look quite similar to the thoroughbreds. We are currently collaborating with Quentin Cronk at the University of British Columbia, Canada, in order to perform genetic tests on all the known individuals. The information should also enable us to identify the most genetically diverse individuals, so that we can preserve as much of the original gene pool as possible. Once this information is known, we hope to obtain pure seed and cultivate large numbers of offspring. This will not only help us to build-up a healthy gene and seed bank, but will also provide material for a reintroduction programme to other suitable sites.
In addition to our Canadian partners, the work is being conducted in collaboration with St Helena Government’s Endemic Plant Nursery, and has been generously funded through a grant awarded by the Mohammed Bin Zayed Foundation.