Commidendrum is a small genus of trees and shrubs in the family Asteraceae (daisy family), comprising five species — including one extinct — all of which are endemic to the remote island of Saint Helena in the South Atlantic Ocean. It belongs to the tribe Astereae, and its closest living relatives are the South African shrub genera Felicia and Amellus, reflecting the genus's likely origin from a southern-hemisphere Asteraceae ancestor. The genus was formally described by Augustin Pyramus de Candolle in 1836.
Members of the genus are small trees growing to 5–8 metres tall, typically developing an umbrella-shaped canopy at maturity. Leaves are arranged in whorls, 7–10 cm long, with toothed margins; the texture is fleshy and the surface sticky and hairy. Flower heads are borne terminally on long, drooping stalks; ray florets are white and disk florets pale yellow, with each head measuring 2–3 cm across.
The most familiar species, Commidendrum robustum (Saint Helena gumwood), was once the dominant tree of the island's mid-elevation woodlands between 300 and 600 metres. It was extensively harvested for fuel after European settlement and is now critically endangered, with fewer than 700 mature individuals surviving. Commidendrum rugosum (scrubwood) and Commidendrum spurium (false gumwood) are also endemic to Saint Helena. Commidendrum burchellii is recorded only from historical specimens and is considered extinct. The gumwood was designated the national tree of Saint Helena in 1977, and conservation replanting efforts have been ongoing since the late 1980s.
Etymology
The genus name Commidendrum likely derives from the Greek kommi (gum) and dendron (tree), reflecting the resinous wood and the common name "gumwood" applied to its members.
Distribution
All species of Commidendrum are endemic to Saint Helena, a small volcanic island in the South Atlantic Ocean. Before human settlement, gumwood woodland covered a substantial portion of the island between elevations of 300 and 600 metres. Today, surviving natural populations are restricted to just two locations on the island, making Commidendrum one of the most range-restricted plant genera on Earth.
Ecology
Commidendrum trees formed two distinct woodland communities on Saint Helena: a moist gumwood woodland along the central ridge at 500–650 metres, and a dry gumwood woodland occupying the lower slopes at 300–500 metres. These woodlands once covered a significant portion of the island and supported the mid-elevation ecology of Saint Helena before large-scale habitat destruction following European settlement.
Conservation
The genus is critically threatened. Commidendrum robustum is estimated to have only 679 mature individuals remaining in the wild, confined to Peak Dale and Horse Point Plain on Saint Helena. Habitat loss through overgrazing by introduced animals and historical timber cutting has driven the decline. Active conservation efforts include exclosure fencing at Peak Dale and the Millennium Grove Forest Project, which has replanted hundreds of trees at Horse Point Plain since 1988. Commidendrum burchellii is already extinct.
History
After the English East India Company settled Saint Helena, gumwood trees were heavily cut for fuel. By 1868 the naturalist John Charles Melliss estimated only 1,300–1,400 individuals remained across the island. Commidendrum robustum was formally described by William Roxburgh in 1816 as Conyza robusta and transferred to Commidendrum by de Candolle in 1836. In 1977 the gumwood was designated the national tree of Saint Helena.
Taxonomy Notes
Commidendrum belongs to the tribe Astereae within Asteraceae. Its closest extant relatives are the South African genera Felicia and Amellus, suggesting a southern-hemisphere origin and long-distance dispersal to Saint Helena. Melanodendron integrifolium (black cabbage tree), also endemic to Saint Helena, is a close relative, and the two genera likely share a common ancestor. Molecular phylogenetic work by Eastwood, Gibby, and Cronk (2004) examined the relationships within arborescent Astereae.
