Commidendrum rugosum 

Scope: Global
Language: English

Translate page into:

Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Asterales Asteraceae

Scientific Name: Commidendrum rugosum (Dryand ex Aiton) DC.
Common Name(s):
English Scrubwood
Aster glutinosus Roxb. in Beatson
Aster rugosus (Dryand) Melliss
Conyza rugosa Dryand. ex Aiton
Taxonomic Notes: Anomolous plants at Deep Valley and Horse Point are possibly hybrids between Gumwood and Scrubwood. There is considerable variation to be found in leaf shape in different parts of the island, possibly due to genetic drift but probably partly related to local environmental conditions.

Assessment Information [top]

Red List Category & Criteria: Vulnerable B1ab(iii)+2ab(iii) ver 3.1
Year Published: 2016
Date Assessed: 2015-07-31
Assessor(s): Ellick, S. & Lambdon, P.W.
Reviewer(s): Clubbe, C.P.
Contributor(s): Cairns-Wicks, R.

Scrubwood (Commidendrum rugosum) has an extent of occurrence and area of occupancy of less than 100 km2 and is found at less than ten (approximately seven) locations across St Helena. As the population trend is somewhat complex, with expansions in some areas and declines in others, it is somewhat difficult to be certain of a continuing overall decline. However, it seems more likely that the trajectory is still downward, and the future threat posed by African Fountain Grass (Pennisetum setaceum (Forssk.) Chiov.) is likely to shift the balance further in future years. We therefore adopt a cautious approach and conserve the species’ threatened status for the time being. This stance could change if a clearer pattern emerges by the next revision.

In the most recent previous red list assessment, Cairns-Wicks (2003) listed the species as Vulnerable under D2. This category no longer applies because, as a result of more detailed survey data, the area of occupancy and number of locations have both been revised upward. However, the population trend has also been reassessed from “Increasing” to ”Decreasing”, and Vulnerable status is therefore maintained under criterion B.

Previously published Red List assessments:

Geographic Range [top]

Range Description:

The extent of occurrence (EOO), based on the area of a minimum convex polygon around known localities, is 94.8 km2. The area of occupancy (AOO), based on a 2 km × 2 km grid, is 84 km2.

Found mainly scattered on the Crown Wastes, mostly above south and east-facing coasts, with the largest subpopulations in the south-west (Man & Horse cliffs; around Blue Point and Distant Cottage Cliffs), where extensive colonies still persist on the less accessible slopes. Elsewhere, small fragments of Scrubwood habitat survive in a number of localities, including Flagstaff Hill, Pipe Path, The Barn, Great Stone Top and along the lower elevation south-facing crags of the Central Ridge. In total, Scrubwood habitat may cover over 50 ha.

Countries occurrence:
Saint Helena, Ascension and Tristan da Cunha (Saint Helena (main island))
Additional data:
Estimated area of occupancy (AOO) - km2:84
Number of Locations:7
Lower elevation limit (metres):100
Upper elevation limit (metres):580
Range Map:Click here to open the map viewer and explore range.

Population [top]


A census carried out in 2013- 2014 estimated the world population to consist of 34,603 mature individuals (approximate 95% confidence range: 30,310 – 43,174). The various localities can be approximately divided between seven locations. The two largest subpopulations are found along Man & Horse cliffs (43.6%) and around Blue Point and Distant Cottage cliffs (43.2%). Smaller subpopulations are located at The Barn (3%), Flagstaff (2.8%) and along the Central Ridge (2%). The Scrubwood is one of the more successful dryland endemics, and in a few areas such as Man & Horse cliffs, is the dominant species.

This assessment gives a much larger estimate of the population total than previous assessments (e.g. cairns-Wicks 2003); however, it is likely that the number of plants has been greatly underestimated in the past, due to the difficulty of accessing and counting the Scrubwoods located on the cliffs. In this census, photographs of the cliff faces were taken and studied in detail in order to estimate the number of Scrubwoods on the cliffs. Thus, there is no real evidence to show an overall increase in the global population. 

Current Population Trend:Decreasing
Additional data:
Number of mature individuals:34603
No. of subpopulations:14

Habitat and Ecology [top]

Habitat and Ecology:

Scrubwood is a species of dry, predominantly coastal habitats between 100 – 580 m. As such, it is able to tolerate moderate drought conditions and cope with slightly saline soils. There is some variation in leaf shape between and within subpopulations.

The species flowers year round, with pollination occurring via by insects: small moths, flies, bees and butterflies. Unlike some other Commidendrum species Scrubwood is strongly self-fertile and produces abundant seed which spreads efficiently and germinates well in the wild; however, few seedlings survive to adulthood.

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

Threats [top]

Major Threat(s):

The settlement of St Helena and the consequent introduction of goats (Capra hircus) led to a decline in the Scrubwood population and the species became confined to refuges on the cliffs, where the Goats could not reach the plants. Extirpation of feral livestock led to re-colonization of a few slopes from the 1960s onward. In particular, the Turk’s Cap subpopulation increased from 10 plants in 1986 to 325 in 2014. At Blue Point, numbers may well also be increasing naturally, especially at Distant Cottage; observations by local conservationists assert that the species has expanded substantially from cliffs refuges onto the adjacent plateau over the past 30 years. However, at other sites Scrubwood numbers have almost certainly declined, most heavily at Flagstaff and Powell’s Valley where competition from invasive weeds has resulted in considerable habitat degradation. The colonies at Cole’s Rock and in Turk’s Cap Valley are also likely to be under threat, with little recruitment.

Scrubwood is very sensitive to grazing as the leaves do not regenerate once shoots have been grazed. Present grazing threats include rodents (particularly Mice (Mus musculus) which feed on the gummy petiole bases), Rabbits (Oryctolagus cuniculus) and feral livestock (mainly Sheep, Ovis aries); these pose a severe threat to the population if not controlled. There is also aggressive competition in some areas from invasive species such as Wild Mango (Schinus terebinthifolia Raddi), Tungy (Opuntia elatior Mill. and O. ficus-indica (L). Mill.) and Creeper (Carpobrotus edulis (L.) N.E.Br.) which is highly likely to be the cause of future continuing decline to the extent and quality of Scrubwood habitat. African Fountain Grass, a competitive non-native species which excludes competitors by forming dense monocultural stands, also poses a significant threat for future Scrubwood habitat. Fountain grass is spreading rapidly across the south-western part of St Helena and presents an imminent threat to the main strongholds at Man & Horse and Blue Point.

One subpopulation has sustained some losses through damage resulting from the construction of the island’s new airport, though with construction almost complete this activity is not a long-term threat to the population.

There is also concern over the potential threat of hybridization of this species with the Gumwood (Commidendum robustum (Roxb.) DC.); however, the rate of introgression appears to be low and the species grow (or recently grew) together at two entirely wild localities with most specimens remaining apparently pure bred.

Conservation Actions [top]

Conservation Actions:

 The species is currently protected under the Endangered Species Ordinance, which will be superceded by the Environmental Protection Ordinance (presently in the final stages of drafting) which is hope to be introduced in 2016.

In addition, several populations are located within the recently designated National Conservation Area (NCA) network; the two largest subpopulations are included within the Sandy Bay National Park. Within the boundaries of the NCAs the species will have further protection under via specific NCA Development Plans (in development).

Attempts have occasionally been made to plant Scrubwood back into the wild at Blue Point, but establishment success is low. The dry, nutrient-poor soils exposed to strong winds present a challenging environment. Rodent baiting and some control of invasive plants has also been undertaken at this site, although this has been entirely dependent on project funding and is unlikely to continue in the future.

The St Helena Government’s Terrestrial Conservation Section undertakes invasive plant control at Powell’s Valley, as well as operating a Scrubwood seed collection and storage programme to aid future conservation work. Seed is also held at the Millennium Seed Bank in the UK.

Scrubwood is also planted in endemic gardens in schools and in gardens around the island to raise awareness of the island’s endemic species.

Citation: Ellick, S. & Lambdon, P.W. 2016. Commidendrum rugosum. The IUCN Red List of Threatened Species 2016: e.T37828A67370570. . Downloaded on 20 June 2018.
Disclaimer: To make use of this information, please check the <Terms of Use>.
Feedback: If you see any errors or have any questions or suggestions on what is shown on this page, please provide us with feedback so that we can correct or extend the information provided