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Mellissia begonifolia 

Scope:Global
Status_ne_offStatus_dd_offStatus_lc_offStatus_nt_offStatus_vu_offStatus_en_offStatus_cr_onStatus_ew_offStatus_ex_off

Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Solanales Solanaceae

Scientific Name: Mellissia begonifolia
Species Authority: (Roxb.) Hook.f.
Common Name(s):
English Boxwood
Synonym(s):
Mellissia begoniifolia (Roxb.) Hook.f. [orth. error]
Physalis begonifolia Roxb.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered B1ab(iii,iv,v)c(i,ii,iii,iv)+2ab(iii,iv,v)c(i,ii,iii,iv); C2a(i,ii)b; D ver 3.1
Year Published: 2016
Date Assessed: 2015-06-13
Assessor(s): Lambdon, P.W. & Ellick, S.
Reviewer(s): Clubbe, C.P.
Contributor(s): Cairns-Wicks, R.
Justification:
The world Boxwood (Mellissia begonifolia) population is confined to a single, very restricted locality. Plants are short-lived and the exact total varies substantially, but it does not exceeded 50 mature individuals, or at least it has not done so for a number of years. On occasions the standing crop has disappeared entirely, with survival of the population dependent on regeneration from a seed bank. These factors alone is sufficient to satisfy the requirements for Critically Endangered status under criteria B, C and D.
Previously published Red List assessments:
  • 2003 – Critically Endangered (CR)

Geographic Range [top]

Range Description:Boxwood is endemic to the island of St Helena, South Atlantic Ocean, where it survives at a single locality on the steep, dry slopes bordering the south coast.

The extent of occurrence (EOO), based on the area of a minimum convex polygon around known localities, is 113 m2. The area of occupancy (AOO), based on a 2 km × 2 km grid, is 4 km2. Following IUCN Red List Guidelines, the EOO is therefore increased to 4 km2 to match the AOO.

The much depleted population persists only in a single, very restricted patch on a boulder field below Lot’s Wife, where a dense cluster of several shrubby plants emerge in most years, crowded into an area no more than 6 m across.

The original native range of this species remains poorly known. It was already rare by the early 19th Century when the first detailed notes on St Helena’s flora were made. Burchell (1805-10) recorded it from Long Range and Little Stone Top (where one adjacent low summit still bears the name of ‘Boxwood Hill’). Melliss (1875) only specifically noted it from Long Range but also added “… and the south-eastern parts of the coast”.
Countries occurrence:
Native:
Saint Helena, Ascension and Tristan da Cunha (Saint Helena (main island))
Additional data:
Estimated area of occupancy (AOO) - km2:4Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):YesEstimated extent of occurrence (EOO) - km2:4
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):Yes
Number of Locations:1Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:NoLower elevation limit (metres):200
Upper elevation limit (metres):450
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Following the botanical works of the 19th Century, no further records were made for some time and the species was thought to be extinct by the late 20th Century. In 1998, the current patch was rediscovered by local conservationist Stedson Stroud. Despite the tiny extent of the population, it has persisted here for at least 17 years. This is all the more remarkable in view of the extreme fluctuations in population size. When rediscovered there were only 1 living and 6 dead plants present. In 2001 there were 6 and by 2003 numbers had risen to 16. In 2007-2008, efforts were made to water the plants during the dry summer months and numbers appear to have peaked at this time, with 33 in 2008 and 35 in 2009. However, by 2010, no mature individuals survived. In 2012 there were eight, but these also died. In 2013 several large immature plants reappeared, but none had matured by the summer and only 1-3 of them survived to flower in 2014.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:1-3Continuing decline of mature individuals:Yes
Extreme fluctuations:YesPopulation severely fragmented:No
No. of subpopulations:1Continuing decline in subpopulations:Yes
Extreme fluctuations in subpopulations:YesAll individuals in one subpopulation:Yes

Habitat and Ecology [top]

Habitat and Ecology:

The ecology of Boxwood remains something of a mystery as the current population can barely be said to be flourishing in a healthy, functioning state. At Lot’s Wife it grows on moderately rich soil accumulated in pockets between boulders. Situated at low altitude, the location receives little rainfall, with the few significant showers mainly confined to the winter months. This habitat may well be moderately representative of that formerly occupied. From what is known of the original range, there appeared to be a preference for dry, rocky places on the south-facing coastal hills at altitudes of 200 – 450 m.

Melliss (1875) described the species growing in ‘clumps’ of several stems up to 6 m across. It is not entirely clear whether he was referring to dense clusters of several individuals (as in the surviving colony) or to single large specimens. However, the height of 8 ft (approximately 2.4 m) which he recorded is considerably in excess of modern specimens. Today, the tallest individuals are little over 1 m. The ethnobotany collection at the Royal Botanic Gardens, Kew, also contains old fragments of trunk with a diameter of at least 9 cm, which is substantially larger than any individual stem has attained in recent times.

In addition to a reduction in size, there appears to have been a regression towards a shorter life-span. The historical specimens were clearly capable of growing to persistent shrubs. Whilst modern plants are somewhat shrubby, they are often reduced to an almost annual phenology, although large specimens can survive for 2-3 years. Generally, substantial numbers of seedlings germinate after the earliest winter rains, which typically fall in March or April. In good years, up to 300 have been recorded. However, most of these die rapidly and only a few survive to adulthood. Maturation takes up between 7 and 12 months depending on the winter conditions.

Adults flower prolifically and appear to be pollinated mainly by small flies. The semi-dry capsules later drop close to the adult, along with large numbers of dead leaves which eventually decay and help to improve the soil for subsequent generations.

Systems:Terrestrial
Continuing decline in area, extent and/or quality of habitat:Yes
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s):

Boxwood is threatened with imminent extinction in the wild, and faces a number of problems. The first of this arises from the very small extent of the world population, which leaves the only colony very vulnerable to chance catastrophes. It is possible that seed could occasionally be taken and distributed by non-native finches or Mynas (Acridotheres tristis L.), but there appear to be few natural dispersal mechanisms and the chances of spread are low. Attempts to seed individuals more widely on the boulder field have been unsuccessful.

Plants are vulnerable to desiccation and require wet winter conditions to survive to maturity. Rainfall patterns can be highly unpredictable, and persistence therefore depends heavily on the presence of a large seed bank. There are probably tens of thousands of seeds buried amongst the few inhabited boulders, which have accumulated over a number of years. However, there is some concern that this resource may have become depleted recently. Peak germination typically produced 300 seedlings between 2008 and 2010, but fewer than 80 seedlings emerged in 2013 and 2014. The decline may have been partially attributable to heavy seed collection, but also to a succession of poor years for adult survival, resulting in little replenishment. Unfortunately, it is difficult to be certain whether the trends are meaningful, and the downturn may yet lie within the boundaries of normal variability.

It is more certain that the modern Boxwood population suffers considerably from herbivory by introduced insect pests. Plants are often densely infested with aphids and Mealybugs (Pseudococcus spp.). These in turn attract predators such as hoverflies and ladybirds (Cryptolaemus montrouzieri Muslant) which may help to limit the infestations. However, the plants usually sustain obvious signs of impairment and appear to experience considerable mortality as a result. A further threat could come from Spider Mite (Tetranychus spp.), which has not yet been detected in the south of St Helena but is already prevalent in the gardens in Jamestown, where it attacks and kills cultivated Solanaceae species and can be very difficult to control.

Invasive weeds present a less serious threat, although species such as Lantana (Lantana camara L.), Tree Tobacco (Nicotiana glauca Graham) and Wild Mango (Schinus terebinthifolia Raddi) are widespread in the locality and could overgrow the Boxwood patch. Periodic weeding by conservationists has probably kept the problem under control thus far. In addition, there are a number of other introduced annual and perennial herbs scattered across the dry coastal hills of St Helena which act as hosts for Mealybug, and probably represent a more substantial management problem.

A large part of the historical loss was a likely consequence of the huge goat population (Capra hircus.) which built-up on St Helena following their release by Portuguese mariners in the early 1500s. These are widely thought to have devastated the vegetation of dry coastal areas over the following centuries. The Goats have now been almost eradicated, but rabbits (Oryctolagus cuniculus) remain widespread and efficiently destroy seedlings of many species.

 

Ultimately, the decline of the Boxwood may have been largely a result of an inability to cope with introduced pests, competitors and diseases, against which most of the arriving non-native flora has some resilience. However, the loss of vigour which appears to have occurred since the 1800s seems extreme, and is difficult to explain. It may be a result of inbreeding amongst the tiny population, greatly reducing the gene pool and causing associated health problems. Melliss noted that the leaves had a strong scent, whereas modern plants often have little. This may indicate a declining ability to produce the toxic alkaloids which confer protection against many herbivores. It is therefore not necessarily the case that Boxwood is intrinsically a ‘weak species’, and could have fared better had it survived to the modern era of conservation in greater numbers.

Conservation Actions [top]

Conservation Actions:

St Helena is in the process of developing a National Protected Areas Network, and the wild Boxwood population is due to fall within the Sandy Bay National Park. It  will thus be protected under the National Conservation Area development plans. The species will also be protected under the new Environmental Protection Ordinance, in the final stages of drafting and expected to be issued in 2016.

Following the rediscovery in 1998, seed was collected and used to establish a cultivated population on St Helena and at the Royal Botanic Gardens, Kew, in the UK. By 2003 there were approximately 50 plants in cultivation and seed orchards were established at Distant Cottage. However, these proved to be difficult to maintain due to their remote locality. The plants need regular attention to provide water, treat pests and collect the capsules which falls relatively soon after maturing. A further seed orchard was later established on Weather Station Ridge and healthy quantities of seed have now been amassed by St Helena Government’s Environmental Conservation Section. Samples have been placed in long-term storage on-island and at Kew's Millennium Seed Bank in the UK.

Despite the successes, the short lifespan of the modern Boxwood plants ensures that regular effort is necessary just to maintain numbers in cultivation. Production has currently dropped due to declines in the Weather Station Ridge seed orchard. An alternative, more convenient location is required, together with a plan to provide dedicated long term management of the resource, as ECS staff are currently stretched due to numerous other demands.

In the longer-term, some form of reintroduction efforts are clearly needed. It is unlikely that these will be successful unless large soil seed reserves can be established in very localised areas, much as in the wild population. The micro-sites also need protection from grazers, and sufficient winter rain to regenerate, but not too much since this will encourage excessive weed competition. Even if these requirements can be fulfilled, the vulnerability to invertebrate pests is still a significant barrier. Additional genetics studies and a selective breeding programme may offer the only realistic hope of restoring a viable population to the hills of St Helena.


Citation: Lambdon, P.W. & Ellick, S. 2016. Mellissia begonifolia. The IUCN Red List of Threatened Species 2016: e.T44011A67372413. . Downloaded on 01 July 2016.
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