Commidendrum rotundifolium 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Asterales Asteraceae

Scientific Name: Commidendrum rotundifolium (Roxb.) DC.
Common Name(s):
English Bastard Gumwood
Psiadia rotundifolia (Roxb.) Hook.f.
Solidago rotundifolia Roxb.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered D ver 3.1
Year Published: 2016
Date Assessed: 2015-06-20
Assessor(s): Lambdon, P.W. & Ellick, S.
Reviewer(s): Clubbe, C.P.
Contributor(s): Darlow, A. & Cairns-Wicks, R.

Given the extreme decline to a single individual, the Bastard Gumwood (Commidendrum rotundifolium (Roxb.) DC.) must qualify as Critically Endangered under criterion D based on the current static population. The loss of the second location at Horse Pasture has occurred within a single generation, and therefore there has been a reduction (this cannot be treated as a continuing decline as once the last remaining individual is gone the species will effectively become Extinct in the Wild until such time as the reintroduced cultivated plants can be counted).

The species was assessed as Extinct in the Wild by Cairns-Wicks (2003). The change of threat category does not represent a genuine increase in numbers because although the surviving wild tree had not been found at this time it was certainly already mature.

Previously published Red List assessments:

Geographic Range [top]

Range Description:The Bastard Gumwood is restricted to a single locality on the south-western coastal hills of St Helena, South Atlantic Ocean.

The extent of occurrence (EOO), based on the area of a minimum convex polygon around known localities, is 13 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 world population is now represented by only one remaining wild tree, discovered in 2009 growing on a cliff at Botley’s Ley, 375 m altitude.

The Bastard Gumwood has been very rare since at least the mid 18th Century, before which the botanical history of St Helena was poorly known. However, since the few recorded localities are very widely scattered, it is likely that the distribution once encompassed much of the mid-altitude zone. In the late 19th Century, plants survived only at Longwood (the last individual died in 1897) and Horse Pasture (two individuals, but the precise locality was subsequently forgotten). Throughout much of the 20th Century the species was assumed to be extinct, but a single tree was rediscovered, also at Horse Pasture (perhaps one of the original individuals), in 1982. This tree died just four years later.
Countries occurrence:
Saint Helena, Ascension and Tristan da Cunha (Saint Helena (main island))
Additional data:
Estimated area of occupancy (AOO) - km2:4
Extreme fluctuations in area of occupancy (AOO):No
Extreme fluctuations in extent of occurrence (EOO):No
Number of Locations:1Continuing decline in number of locations:Yes
Lower elevation limit (metres):350
Upper elevation limit (metres):450
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Only one wild individual survives, though a small cultivated population is also in existence on St Helena.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:1
Extreme fluctuations:No
No. of subpopulations:1
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:Yes

Habitat and Ecology [top]

Habitat and Ecology:

There is little information with which to reconstruct details of the ecology of this species. All known historical localities are between 350 and 450 m altitude, suggesting a preference for reasonably dry hill-slopes, perhaps in the transitional zone between the arid lowlands and the more heavily wooded uplands. Above 400 – 450 m, forests of the closely-related Gumwood (Commidendrum robustum (Roxb.) DC.) once dominated large areas.

The surviving Bastard Gumwood trees (wild and cultivated) generally flower in summer, but there is significant variation between individuals and between years. They are inhibited from self-fertilizing through a genetic incompatibility mechanism which operates at two positions on the genome. If pollen comes from an individual with the same alleles at both loci then it will be rejected when it germinates on the stigma surface. As a result of this mechanism, natural viability of seed in the surviving plants is very low, although approximately 0.01% remains fertile through ‘leakage’ (i.e., pollen evading the defences).

Movement patterns:Not a Migrant

Use and Trade [top]

Use and Trade: Was probably used as firewood and timber in the past.

Threats [top]

Major Threat(s):

The presumed dramatic decline of the Bastard Gumwood is thought to have been largely attributable to very high grazing pressure from Goats (Capra hircus). Goats were introduced by Portuguese sailors in the early 16th Century, and flourished in large numbers until concerted control measures lead to their near eradication between the 1950s and 1970s. Across the dry, mid-altitude hills, much of the original native vegetation cover was lost during the intervening years. In the early days of the British colony, there was also a great demand for timber and firewood, and it is likely that a substantial number of trees were felled with little heed given to stewardship of such important resources. However, as the island was not settled for more than 150 years after the first Goats arrived, it is unclear how many trees survived into The Colonial Period. Later accounts indicate that the species was extremely rare by the mid 1700s.

Today, the main barrier to the persistence of the population in the wild is a lack of recruitment. The self-compatibility mechanism ensures that almost all seed is sterile, and there is thus very little chance of seedlings establishing naturally. Meanwhile, artificial cross pollination has proved difficult. The tree is growing on a sheer cliff, only accessible by abseiling, and is also in an awkward position which makes it very difficult to reach the flowers.

In addition, the health of the tree is threatened by outbreaks of Jacaranda Bug (Insignorthezia insignis (Browne)). Thus far, these outbreaks have been periodic and at least partially curtailed by the presence of the ladybird (Hyperaspis pantherina Fürsch), which was introduced to St Helena as a biocontrol agent in the 1990s. Cultivated trees have been similarly affected by Mealybug (Pseudococcus spp.) and various Aphid species, which may require periodic chemical treatment. The honeydew from these pests sustains  growths of black, sooty mould, which can quickly coat the leaves and reduce photosynthesis if left unattended.

Conservation Actions [top]

Conservation Actions:

Following the rediscovery of the Horse Pasture tree, seed was collected and several daughters were propagated (Cairns-Wicks 2009). By 2009 these had dwindled to a single individual located at Pouncey’s, which was in poor condition. Further propagation attempts had been unsuccessful because, although germination was found to be moderately good, all saplings proved to be of hybrid origin. The tree had crossed with False Gumwoods (C. spurium (G.Forst.) DC.),  growing at a nearby nursery, to produce fertile offspring.

In order to rectify the problem, in 2010 a cage of insect-proof mesh was erected around the remaining Bastard Gumwood to exclude pollinators, and an intensive programme of hand-pollination and seed collection was undertaken by a collaboration of Government staff, the St Helena National Trust and local volunteers. Large quantities of seed were sown, and despite the low germination rate, over 100 saplings were reared in the first year.

Whilst the emergency rescue programme was being implemented, the wild tree at Botley’s was discovered. The presence of a second individual offered the possibility of increasing genetic diversity and overcoming the self-incompatibility barrier (assuming that the two plants belonged to different compatibility groups). A small amount of pollen was obtained from Botley’s in the first season and crossed to a few inflorescences at Pouncey’s, but the seed was accidentally mixed during collection and thus it is not know whether viability was enhanced.

Subsequently, the intensive propagation work has continued as a result of two restoration projects (funded by JNCC and OTEP). Seed from both parents have now been cultivated, and saplings reared together at three locations. Those transplanted to High Hill have not fared particularly well, but over thirty mature trees are now growing at Drummond’s Point. These have flowered and produced seed. The extent of cross pollination between the genotypes is not clear, but the germination rate has increased by at least 1000% in these second generation plants (pers. comm., A. Darlow 2014). In March 2015 two self sown seedlings were discovered beneath these second generation plants. A third group of over 100 plants has been established in the Agriculture and Natural Resources complex at Scotland.

The success of the recovery work to date has provided some hope of re-establishing a stable Bastard Gumwood population in the future. However, while numbers are still very low, the cultivated sites are very vulnerable and plants remain in need of regular attention as they are subject to heavy pest outbreaks. Ants are very abundant at Drummond’s Point, and actively spread sap-sucking pests between hosts in order to feed on their honeydew. Furthermore, the work will soon have to be taken forward without dedicated funding. It is hoped that staff of St Helena Government’s Environmental Conservation Section will maintain a more limited maintenance programme in the short-term.

Citation: Lambdon, P.W. & Ellick, S. 2016. Commidendrum rotundifolium. The IUCN Red List of Threatened Species 2016: e.T37591A67370300. . Downloaded on 22 June 2018.
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