Diversity and Conservation of Comoro Island Palms: Mission Report 2023 & 2024

The Comoro Islands is an archipelago of four main oceanic islands, volcanic in origin, lying in the Mozambique Channel of the Indian Ocean between the northern tip of Madagascar and the east coast of Africa (Plate 1). The plant diversity of the Comoros, which total just over 2,000 km² in surface area across four main islands, is extraordinarily rich with around 1,000 native species, 30% of which occur nowhere else. The fauna is equally remarkable, including 17 endemic bird species, nine endemic reptiles and two endemic fruit bats (such as the charismatic Livingstone’s fruit bat). The fauna is largely dependent on the forest. However, limited intact forest remains on Anjouan and Mayotte, while the forests of Mohéli and Ngazidja (Grande Comore) are badly degraded, except at higher elevations. The major drivers of vegetation transformation are land clearance for agriculture and construction, and invasive exotic plant species, the impacts of which are exacerbated by cyclones that are frequent in the region and likely to intensify due to climate change.

Palms are keystone species in tropical forests, acting as “ecosystem engineers” and providing numerous services to other wildlife. Four species of palm are endemic to the Comoro Islands. Three are already known to be threatened with extinction according to the IUCN Red List of Threatened Species: Ravenea moorei (Critically Endangered), Ravenea hildebrandtii (Endangered) and Chrysalidocarpus lanceolatus (Vulnerable). The fourth, C. cabadae, was discovered in cultivation, having been described from material growing in a garden in Cuba (Moore 1962), but reports have emerged of its presence in the wild in Mayotte (Barthelat & Viscardi 2012). A further species name exists, C. humblotianus, but it has not been reported in the wild since 1884. A further species known in cultivation as Chrysalidocarpus “Mayotte” has also been reported, but confirmed field observations are lacking. To better understand this important group of plants, a concerted field campaign with associated taxonomic research is required. The inadequate taxonomic foundations of the Comoro palms represent an existential threat to their long-term survival.

Uniquely among botanic gardens, all three of the better-known species of Comoro palm are cultivated in the Palm House at the Royal Botanic Gardens, Kew. However, a forthcoming renovation of the Palm House will result in the removal of all plants from the building. This raises concerns about the long-term survival of these important collections. Of intense concern is Ravenea moorei, which is unknown from cultivation in any other botanic or private garden. Moreover, prior to the missions described in this report, little was known of the state of wild populations (Keith et al. 2006). Ravenea moorei is a majestic, coconut-like palm with stems reaching 20 m tall and 11-35 cm diameter, and leaves up to 3 m in length. The first specimens of R. moorei were made in Ngazidja in the 1960s, although these were at first confused with R. hildebrandtii (Moore 1965, Dransfield & Uhl 1986). It is known only from forest on basalt at 600-1000 m on the western flanks of Mt. Karthala, an active volcano. The extent and current state of the population is unknown, raising concerns that it may be on the brink of extinction. Although seeds of R. moorei from the type collection were distributed to multiple gardens, the Kew palm is the last authenticated survivor in cultivation. The palm is dioecious, the Kew specimen being male, and therefore cannot be propagated. Given its size and maturity, it is unlikely that this palm can be moved successfully. It was the potential global significance of this cultivated palm, which will likely be lost during the preparation for the Palm House renovation, that was the initial driver for the work described in this report.

Through two missions to the Comoro Islands in November 2023 and November 2024, we aimed to establish an integrated, collaborative programme on the diversity and conservation of Comoro palms to:

1.      Address the major knowledge gaps in our understanding of the diversity and taxonomy of Comoro palms and identify new species, if any exist, drawing on Kew’s >30-year research experience on Indian Ocean palms.

2.      Document the distribution, population status and threats to all Comoro palm species as a fundamental baseline for updated IUCN extinction risk assessment.

3.      Undertake training in the Comoro Islands, targeted at key stakeholders, in palm biology, including taxonomy, field skills and cultivation, to build in-country capacity for palm conservation.

4.      Establish ex situ collections of palms on the Comoro Islands, and potentially elsewhere, developing in-country horticultural skills and infrastructure to ensure long-term sustainability of conservation collections.

5.      Use Ravenea moorei and the Comoro palms as a case study for public engagement on extinction and conservation of tropical palms and the forest that they inhabit in the renovated Palm House and via appropriate mechanism in the Comoro Islands.