|Scientific Name:||Wahlenbergia angustifolia (Roxb.) A.DC.|
Roella angustifolia Roxb.
Wahlenbergia clivosa DC.
|Taxonomic Notes:||The St Helena's Wahlenbergia species are related to each other and probably radiated from a common ancestor on the island. The weakly woody habit and bilocular ovary is distinctive. They form a morphological and ecological series:
1. W. angustifolia – creeping leptocaul with small narrow leaves and few flowered inflorescence.
2. W. linifolia – upright, larger, few flowered inflorescence.
3. W. burchellii- larger leaves, many flowered inflorescence.
W. angustifolia is at the drier end of the series and is the only one which is relatively common. W. burchellii is extinct. (Cronk 2000).
|Red List Category & Criteria:||Vulnerable B1ab(iii,v)+2ab(iii,v) ver 3.1|
|Assessor(s):||Lambdon, P.W. & Ellick, S.|
Although one of the more widespread of St Helena’s endemic plant species, the range of Small Bellflower is comparatively very restricted in global terms. Both the extent of occurrence and area of occupancy are well below the thresholds necessary to qualify as Vulnerable under criterion B, and there is no issue in considering the number of locations to be less than 10. An ongoing decline is more difficult to demonstrate due to a lack of historical data against which conclusions can be drawn. However, it is relatively certain that at least one of the major subpopulations has experienced substantial recent losses, and there are serious threats posed by the spread of invasive species to several other important localities. We consider that these combined factors are sufficient to justify Threatened status.
|Previously published Red List assessments:|
|Range Description:||Small Bellflower is endemic to the island of St Helena, South Atlantic Ocean, where it is restricted rocky, mid-altitude habitats, principally in the south-west and along the Central Ridge.|
The extent of occurrence (EOO), based on the area of a minimum convex polygon around known localities, is 45.0 km2. The area of occupancy (AOO), based on a 2 km × 2 km grid, is 36 km2.
This slender herb is a local species on St Helena. It occurs on scattered ridges and rock outcrops in the south-west of the island, with the largest numbers on the hills around Manati Bay (at Wild Ram Spring and Devil’s Cap). Small subpopulations are also found on Joan Hill, in Thompson’s Valley and at Blue Point. Further inland, the population extends around the arc of the Central Ridge where the plants are more or less restricted to the south-facing crags just below the summit. Colonies occur reasonably continuously along this stretch of habitat, but barely extend further east than Cole’s Rock except for isolated clusters on a roadside embankment near Rock Rose and on cliffs in Deep Valley. The species is almost entirely absent from the northern half of the island, although a relict patch survives on Flagstaff Hill which now numbers only two plants.
Native:Saint Helena, Ascension and Tristan da Cunha (Saint Helena (main island))
|Range Map:||Click here to open the map viewer and explore range.|
Following a census of the species conducted in 2013-14, the world population was estimated at 8,803 mature individuals (approximate 95% confidence range: 5,466 – 16,729). By far the most important site was at Devil’s Cap Ridge, where numerous plants were scattered amongst rocks on the southern flank. Overall, this subpopulation accounted for 55.2% of the total. Less than two km away, another large colony (accounting for a further 14.2% of the total) occurred in the vicinity of Wild Ram Spring.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:|
Small Bellflower is a species of rocky escarpments which face the prevailing winds and receive moderate amounts of mist and rain. It typically occurs between 550 and 700 m altitude, but rarely extends down to 450 m or as high as 760 m. There is usually relatively little competing vegetation. Native associates may include the Crevice Fern (Cheilanthes multifida Sw.), Hen-and-Chicks (Asplenium lunulatum Sw.) and Tufted Sedge (Bulbostylis lichtensteiniana (Kunth) C.B.Clarke), with cushions of Mossy Fern (Elaphoglossum furcatum Christ) and the moss Macromitrium urceolatum (Hook.) Brid. at higher elevations. However, the habitats are more often dominated by non-native species which typically include a variety of sparse grasses and annual weeds (e.g. Common Cat’s-Ear Hypochaeris radicata L. and Pale Cudweed Gnaphalium luteoalbum L.).
|Continuing decline in area, extent and/or quality of habitat:||Yes|
Unlike most of St Helena’s endemic species, Small Bellflower has a creeping habitat which allows it to grow through even moderately dense grassland. This has conferred a degree of resilience against invasive competition, although tolerance decreases where the ground cover becomes too luxuriant. Some exceptionally large, shrubby individuals occur at Devil’s Cap, but many of these have now largely been swamped by tall growths of Cow Grass (Paspalum scrobiculatum L.). At Wild Ram Spring, thousands of plants were noted in 2008, but since then there has been a dramatic recent decline which appears to be mainly attributable to encroachment by a thick sward of Kikuyu Grass (Pennisetum clandestinum Hochst. ex Chiov.).
St Helena is currently in the process of developing a National Protected Areas Network, which will eventually encompass almost the entire population. Most importantly, the Central Peaks National Park (designated in 2013) already covers the upland colonies, whereas Sandy Bay National Park will occupy much of the south-west. The bulk of the network is expected to be in place by the end of 2015. The species will also be protected under the new Environmental Protection Ordinance, presently in the final stages of drafting and also expected to be issued in 2015.
|Citation:||Lambdon, P.W. & Ellick, S. 2016. Wahlenbergia angustifolia. The IUCN Red List of Threatened Species 2016: e.T43988A67371447.Downloaded on 21 September 2018.|
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