The flora of Saint Helena, an isolated island in the South Atlantic Ocean, is exceptional in its high level of endemism and the severe threats facing the survival of the flora. [1] In phytogeography, it is in the phytochorion St. Helena and Ascension Region of the African Subkingdom, in the Paleotropical Kingdom.
The endemic plants of Saint Helena include many notable Cabbage Tree or, "insular arborescent Asteraceae", members of the daisy family which have evolved a shrubby or tree-like habit on islands. Other notable endemics include the closely related St Helena redwood ( Trochetiopsis erythroxylon ) and St Helena dwarf ebony ( Trochetiopsis ebenus ). These are unrelated to the redwood trees of California or to the ebony trees of commerce, being instead in the Mallow family (Malvaceae).
Today there are three major vegetation zones: the tree-fern thicket of the highest parts of the central ridge; the pastures of middle elevations and the dry, eroded "crown wastes" of lower elevations. Of these only the tree-fern thicket is a natural vegetation type. The middle elevations were formerly covered with native woodland of gumwoods ( Commidendrum ) and other trees, now largely destroyed. The "Crown wastes" or coastal zones were formerly covered with native scrub, of which a major component was probably St Helena dwarf ebony ( Trochetiopsis ebenus and St Helena tree ebony Trochetiopsis melanoxylon ).
The destruction of the native vegetation began soon after the discovery of the island by the Portuguese in 1502, with the introduction of goats. As there were no native herbivorous mammals, the flora was unadapted to such threats. Later with the establishment of permanent settlement on the island by the English East India Company in 1659, many introduced plants became established which created new vegetation types. Furthermore the native trees were subject to catastrophic cutting for such purposes as housebuilding and to fuel stills for the distillation of arrack. As a result of this legacy many endemic plant species are extinct or critically endangered.
Pteridophytes (Ferns and fern-allies)
The Saint Helena scrub and woodlands ecoregion covers the volcanic island of Saint Helena in the South Atlantic Ocean. The island's remote location gave rise to many endemic species. First discovered and settled in the 1500s, the island has been degraded by human activities. Most of its native habitat has been destroyed, and many of its unique plants and animals are extinct or endangered.
The Saint Helena olive is an extinct species of flowering plant. It is the only member of the genus Nesiota. It was endemic to the island of Saint Helena in the South Atlantic Ocean. Despite its name, it is unrelated to the true olive, but is instead a member of the family Rhamnaceae, the family which contains buckthorns and jujube. The last remaining tree in the wild died in 1994, and the last remaining individual in cultivation died in December 2003, despite conservation efforts. It is thus a prime example of recent plant extinction. The Saint Helena olive belongs to the tribe Phyliceae, which are mostly endemic to Southern Africa.
Lachanodes arborea, the she cabbage tree, is a small tree in the family Asteraceae. It is an endangered endemic of the island of Saint Helena in the South Atlantic Ocean. It is now extinct in the wild.
Melanodendron is a genus of trees in the family Asteraceae, with only one species, Melanodendron integrifolium, native to the island of Saint Helena. It is related to the Saint Helenan gumwoods and is the most common of the remaining cabbage tree species of Saint Helena, although it is considered endangered due to the restricted population size.
Pladaroxylon is a genus of trees in the tribe Senecioneae within the family Asteraceae.
Dicksonia arborescens, the Saint Helena tree fern, is a characteristic plant of the "tree fern thicket" vegetation of the highest parts of the central ridge of the island of Saint Helena. It is the type species of the genus Dicksonia.
Trochetiopsis erythroxylon, the Saint Helena redwood, is a species of plant, now extinct in the wild. It was formerly abundant enough in the upland parts of the island of Saint Helena for early settlers in the 17th century to use the timber to make their homes. It became extinct in the 1950's due to deforestation as its habitat was cleared to make way for pasture, timber and fuel.
Trochetiopsis ebenus, the dwarf ebony or Saint Helena ebony, is a species of flowering plant that is endemic to the island of Saint Helena in the southern Atlantic Ocean. It is not related to the ebony of commerce, but is instead a member of the mallow family, Malvaceae. Saint Helena ebony is now critically endangered in the wild, being reduced to two wild individuals on a cliff, but old roots are sometimes found washed out of eroding slopes. These are collected on the island a used for inlay work, an important craft on Saint Helena. A related species, Trochetiopsis melanoxylon is now completely extinct.
Commidendrum is a genus of trees and shrubs in the family Asteraceae endemic to the island of Saint Helena in the South Atlantic Ocean. The vernacular name is gumwood or scrubwood.
Wahlenbergia roxburghii, the Roxburgh bellflower or dwarf cabbage tree, is an extinct member of a group of four species of Wahlenbergia once known from the island of Saint Helena, in the South Atlantic Ocean. It was last seen by naturalist John Charles Melliss in 1872. William Roxburgh recorded it in the thick forests on the south face of Diana's Peak. De Candolle notes it in dense woods around Diana's Peak and Halley's Mount. Burchell notes it 'On Sandy Bay ridge near Taylor's. Flowering: probably August to March. It was exceedingly rare in Meliss's time, it is not in his book as he had not found it. It was probably the increase of Phormium tenax planting on the ridge that pushed Wahlenbergia roxburghii into final extinction. It is an example of one of the early extinctions of Saint Helena plants as a result of human activity, with a history similar to that of the stringwood, .
Trochetiopsis melanoxylon, the dwarf ebony or St Helena ebony, of the island of Saint Helena is related to Trochetiopsis ebenus but is now extinct. It differed from T. ebenus by having much smaller flowers, sepals hairless on their interior surfaces and leaves densely hairy on both surfaces.
The flowering plant genus Trochetiopsis consists of two extant and one extinct species endemic to the island of Saint Helena. They were formerly placed in the family Sterculiaceae, but this is included in the expanded Malvaceae in the APG and most subsequent systematics.
Commidendrum robustum, the Saint Helena gumwood, is a species of tree endemic to Saint Helena, Ascension and Tristan da Cunha. Though it is now comparatively rare, it was once one of the most abundant trees of mid-elevations of the island of Saint Helena in the South Atlantic Ocean. A small tree to 7–8 m, it was cut extensively for fuel in the early years of settlement of the island by the English East India Company. It has given its name to certain placenames on the island such as "Gumwoods". It is one of several species in the endemic genus Commidendrum.
Mellissia was formerly a monotypic genus in the family Solanaceae with the single species, Mellissia begoniifolia, endemic to the island of Saint Helena. It was named by Joseph Dalton Hooker in honour of John Charles Melliss, a 19th-century engineer and amateur naturalist who worked on Saint Helena. The plant is now known correctly as Withania begoniifolia (Roxb.) Hunz. & Barboza, the genus Mellissia having been subsumed in the genus Withania.
Nesohedyotis is a genus of flowering plants endemic to the island of Saint Helena in the South Atlantic Ocean. It in the family Rubiaceae.
Melhania is a genus of small shrubs or herbaceous plants. Traditionally included in the family Sterculiaceae, it is included in the expanded Malvaceae in the APG and most subsequent systematics. The genus is named for Mount Melhan in Yemen.
Senecio leucadendron is a species of flowering plant in the family Asteraceae, endemic to Saint Helena. It was first described by Georg Forster in 1789 as Solidago leucadendron.
St Helena ebony is a common name for two closely related plants endemic to St Helena. It is inconsistently applied, and either of the following species may be referred to as St Helena ebony, with dwarf ebony used to refer to the other: