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Wahlenbergia angustifolia 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Asterales Campanulaceae

Scientific Name: Wahlenbergia angustifolia (Roxb.) A.DC.
Common Name(s):
English Small Bellflower
Synonym(s):
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).

Assessment Information [top]

Red List Category & Criteria: Vulnerable B1ab(iii,v)+2ab(iii,v) ver 3.1
Year Published: 2016
Date Assessed: 2015-06-17
Assessor(s): Lambdon, P.W. & Ellick, S.
Reviewer(s): Clubbe, C.P.
Contributor(s): Cairns-Wicks, R.
Justification:

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.

In the most recent previous Red List assessment, Cairns-Wicks (2003) classified the species as Endangered B2ab(i,iii), on the basis that no more than five localities were confirmed at the time. Depending on how a location is defined, there may still be an argument for maintaining this status. However, large colonies have since been identified which have substantially expanded the known population, and it seems less appropriate to persist with this higher threat category. It should be noted that the number of plants is unlikely to have increased in real terms since 2003, and has probably contracted to some degree.

Previously published Red List assessments:

Geographic Range [top]

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.
Countries occurrence:
Native:
Saint Helena, Ascension and Tristan da Cunha (Saint Helena (main island))
Additional data:
Estimated area of occupancy (AOO) - km2:36Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:45.0
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:7Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:NoLower elevation limit (metres):450
Upper elevation limit (metres):760
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:

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.

The majority of the remaining population was confined to the Central Ridge, with 1.3% between Hooper’s and Red Rock, 15.0% around High Peak and Mt Vesey and a further 12.7% extending eastward to Cole’s Rock. A large number of the eastern plants were concentrated on one area of crags above Sheep Pound.

Due to substantial recent improvements in coverage, it is difficult to determine whether the population has genuinely changed in recent times. Most locations occur on steep terrain which is often difficult to access or view. The entire sweep of the Central Ridge has probably never been subject to a detailed count previously, and the importance of this habitat greatly underestimated. Other subpopulations were known from verbal reports handed down by past generations of local conservationists, but detailed knowledge had faded with time. However, a few brief accounts provide some indications of declines. There have been clear and dramatic reductions at Wild Ram Spring since 2008, when the colony was very extensive (P. Lambdon and A. Darlow pers. obs.). Cronk (2000) also recorded the species from Great Stone Top, but it has not been detected here for a number of years. Cairns-Wicks (2003) noted the Joan Hill population to be important whereas only 21 plants were recorded there in 2013-14, although it is possible that some patches were missed on the area’s vast expanses of cliff.

Current Population Trend:Decreasing
Additional data:
Number of mature individuals:8803Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:No
Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

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.).

The association with inhospitable crags and crevices has probably allowed this resilient endemic to persist in isolated patches when most of the other native vegetation of the upper-middle altitude belt has vanished. Along the Central Ridge, it survives on a number of rocky scars which have been completely surrounded by dense plantations of New Zealand Flax (Phormium tenax J.R.Forst. & G.Forst.). It overlaps to some degree with species of the cloud forest zone and in a few places may be found near its sister taxon, the Large Bellflower (Wahlenbergia linifolia (Roxb.) A.DC.). The two species are believed to hybridize, which is a source of substantial conservation concern as the latter is now severely threatened with extinction.

Flowers are produced throughout most of the year, but are less plentiful during dry periods or if the plant is heavily shaded. Bees and larger flies are probably the most efficient pollinators. It is unlikely that self-fertilization can occur without them as the anthers shed their pollen in masses on the undersides of the stigmas where they are shielded from the receptive surface. Never the less, there is a regular production of seed with high viability.

Systems:Terrestrial
Continuing decline in area, extent and/or quality of habitat:Yes

Threats [top]

Major Threat(s):

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.).

At a smaller scale, various other competitors may have adverse affects on abundance. In parts of the south-western range, Thatching Rush (Ficinia nodosa (Rottb.) Goetgh., Muasya & D.A.Simpson) is often prevalent, whereas sporadic growths of shrubs such as Lantana (Lantana camara L.), Furze (Ulex europaeus L.) and Wild Mango (Schinus terebinthifolia Raddi) infest suitable areas at all altitudes. In the future, there are serious concerns over the spread of African Fountain Grass (Pennisetum setaceum (Forsk.) Chiov.). This introduced species already blankets large parts of the far western coastal hills with dense, tussocky growths, and it appears to be spreading rapidly westward. The invasion front already borders Manati Bay and Blue Point, where it threatens to overwhelm the major population centres. At high densities, the stands form virtual monocultures and are likely to cause substantial changes to important habitat areas.

Grazing by introduced herbivores presents another threat. The problems are likely to be somewhat less serious than in the past, when feral goats (Capra hircus) were extremely abundant on St Helena. In previous centuries, Goats were probably responsible for destroying most of the native vegetation of lower and middle altitudes. The population was largely eradicated between the 1950s and 1970s, but another introduced species, the rabbit (Oryctolagus cuniculus) is still very widespread and is probably responsible for preventing regeneration of Bellflowers away from the less accessible crags.

Overall, there is little doubt that Small Bellflower is one of the more adaptable of St Helena’s endemic species and is unlikely to be seriously threatened with extinction for the foreseeable future. However, there is almost certainly a trend towards gradual loss of habitat leading to slow, long-term declines, and this insidious problem requires some attention.

Conservation Actions [top]

Conservation Actions:

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.

There is currently little practical management to protect Small Bellflower colonies from invasive threats, and conservation efforts are often constrained by the difficult terrain. Some sites are certainly in deteriorating condition and would benefit from intervention, particularly at Devil’s Cap and Wild Ram Spring. In addition, a management plan to address the spread of African Fountain grass is much needed. It is unlikely that the advance can be stopped, but it may be possible to reduce the rate of spread, and to mitigate against the effects.

Seed collections have been made from a number of localities and stores are currently banked on-island (at St Helena Government’s Endemic Plant Nursery) and at the Millennium Seed Bank in the UK. The species is relatively easy to grow in cultivation, and could even make an attractive garden plant.


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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