|Scientific Name:||Anogramma ascensionis|
|Species Authority:||(Hook.) Diels|
|Taxonomic Notes:||Unambiguously distinct from other Anogramma species, both morphologically and ecologically.|
|Red List Category & Criteria:||Critically Endangered B1ab(iii)+2ab(iii); D ver 3.1|
|Assessor/s:||Lambdon, P.W., Stroud, S., Gray, A., Niissalo, M., Renshaw, O. & Sarasan, V.|
|Reviewer/s:||Clubbe, C.P. & Hilton-Taylor, C.|
Until recently, Anogramma ascensionis was considered to be Extinct (Gray 2003). The only confirmed 20th Century record was made in 1958, when a small population was found on the north side of Green Mountain by Eric Duffey. However, four individuals were rediscovered by Stedson Stroud, Olivia Renshaw and Phil Lambdon in July 2009 (Duffey 1964). Subsequent searches of nearby locations have revealed other small clusters of plants. The total population was estimated to be approximately 40, although as the sporophytes appear to be short-lived and survive for only a few months, not all of these were present concurrently.
The main cause of decline in A. ascensionis has almost certainly been competition from non-native weeds. Aggressive colonists now form relatively dense colonies across many of the areas which probably once constituted optimum habitat (see Threats section). There is no evidence that the spread of such competitors has now ceased, and therefore it seems advisable to consider that the population is threatened by ongoing declines in habitat quality.
|Range Description:||Known only from the Green Mountain area of Ascension Island (to Saint Helena), South Atlantic Ocean.
Rare throughout the recorded botanical history of Ascension Island, although the population was perhaps reasonably healthy at the time of Hooker in 1843, who recorded it from wet banks and rocks on the south and east sides of Green Mountain at an altitude of 350-550 m. The altitude is clearly an error, as these elevations coincide with the drier ground below and at the foot of the mountain. The plants found by Duffey and by the current assessors all lie between 600 and 750 m, where the climate is indeed often moderately damp. The extant population is extremely thinly scattered along the southern slopes, from Summerhouse Ridge westwards. Several plants are dotted along a knife-edged ridge running down to Breakneck Valley, and a group of approximately 25 plants was found on a cinder cliff just beyond the western-most tunnel on Elliot’s Path. The extent of occurrence is approximately 7 ha, and the area of occupancy less than 10 m².
Native:Saint Helena, Ascension and Tristan da Cunha (Ascension)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||With the exception of one larger patch of approximately 25 plants (see Geographic Range), all subpopulations known are extremely small and number only a few individuals. The sporophytes are very small, short-lived and occur in inaccessible locations, and furthermore, the gametophytes are extremely difficult to locate in the wild as they are inconspicuous and are probably confined to deep crevices. This leads to the possibility that numbers may be higher than that currently estimated (40 mature individuals). However, as searches have been reasonably thorough, the current total is unlikely to be a substantial underestimate.|
|Habitat and Ecology:||
All extant individuals occur on sparsely vegetated, vertical cinder banks exposed to the prevailing wind, and thus receive moderately regular moisture from incoming mists. However, those sites at lower altitudes may be subject to arid conditions for long periods. Before the introduction of a large number of weed species to the island from the mid 1800s onward, it seems likely that there would have been much similar habitat across the rock faces of Green Mountain, although most suitable areas are now covered with dense growths of aggressive non-native species, particularly in the damper locations which may once have represented optimum habitat conditions. Known localities are often associated with the native thallose liverwort Plagiochasma rupestre (G. Forst.) Stephani.
A. ascensionis produces green spores which must germinate soon after dispersal. In other Anogramma species, the gametophytes can persist for long periods, propagating vegetatively via gemmae which may have some dormancy capabilities. The sporophytes are short-lived, and only produced under suitable conditions. These features are probably also characteristic of A. ascensionis, which suggests that desiccation of the delicate gametophyte thallus may be a critical limiting factor in survival. Most recently observed plants are very small, reaching no more than 2-4cm high, although from older specimens it is known that heights of at least 10cm were once attained. The diminutive size and persistence of the minute gametophytes ensures that the competitive ability is very low. It is clearly an ephemeral, colonist species, exploiting relatively bare, harsh habitats before later successional communities develop. Potentially suitable habitat areas are now rare on Green Mountain and are likely to suffer further declines.
Invasion by introduced weeds is a serious threat to the long term survival of the species. Relatively bare cinder banks are now rare due to gradual encroachment by a variety of species. Amongst the most important of these are the grasses Sporobolus africanus (Poir.) Robyns & Tournay and Paspalum scrobiculatum L., and broadleaved species such as Clidemia hirta (L.) D.Don and Begonia hirtella Link. Probably the most serious threat is from the maidenhair ferns, Adiantum capillus-veneris L. and A. raddianum C. Presl. These now occur over large areas of moist cinder bank on Green Mountain, the former species predominantly on the south side and the latter on the north side, and are likely to be direct competitors for the moist crevice habitats required by Anogramma gametophytes.
Bank slippages represent another potential threat. As the population is so small, a single slippage could destroy a large proportion of the world total. Grazing by sheep and rabbits could also be harmful, although most plants currently known are too inaccessible to be reached by either species.
In the longer term, increases in exposure to drying conditions on the mountain, brought about by global warming, could further restrict the habitat available to the species.
Green Mountain was declared a National Park in 1996. Due to the low population density on Ascension, there is little human interference in the area and further legislation is not a priority.
Regular weeding is conducted by the Conservation Department to keep invasive species in check. However, larger scale clearance to create new open habitat areas, and restoration of functioning native communities is needed to boost the long-term future of the species.
Recently, attempts have been made to germinate Anogramma ascensionis in cultivation. Staff from the Royal Botanic Gardens, Kew, U.K. have successfully used in vitro techniques to rear gametophytes from spores, achieving a high germination rate. Sporophytes have also been reared on Ascension Island from soil collected around known sites. A long term, sustained programme of cultivation is required to ensure that viable living material is secured.
|Citation:||Lambdon, P.W., Stroud, S., Gray, A., Niissalo, M., Renshaw, O. & Sarasan, V. 2010. Anogramma ascensionis. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 12 December 2013.|
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