''Pladaroxylon'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of trees in the tribe

Senecioneae Senecioneae is the largest tribe of the Asteraceae, or the sunflower family, comprising over 150 genera and over 3,500 species. Almost one-third of the species in this tribe are placed in the genus ''Senecio''. Its members exhibit probably the w ...

within the family

Asteraceae Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...

. The only known species is ''Pladaroxylon leucadendron'', native to the island of

St. Helena Saint Helena (, ) is one of the three constituent parts of Saint Helena, Ascension and Tristan da Cunha, a remote British overseas territory. Saint Helena is a volcanic and tropical island, located in the South Atlantic Ocean, some 1,874 km ...

in the

South Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...

. Commonly known as the he cabbage-tree.

Description

''Pladaroxylon leucadendron'' is a small tree, growing to a maximum of 5 meters in height, with relatively large and cabbage like leaves. On young trees the leaves are very large, often reaching 30 centimeters in length, but on older trees they are usually smaller. They are oval in outline, with a downy underside, and very prominent veins. The trees branch at regular intervals into two equal sized limbs and all the leaves are at the furthest ends of the branches. The first branching is at 1.2–2 meters above the ground. The tree has a broad, rounded canopy when full grown. As typical of the family it has flower heads () with many flowers crowded together in one structure that resembles a single flower, each about 6 millimeters in width. Each of these flower heads grows together with many others in a cluster called a

corymb Corymb is a botanical term for an inflorescence with the flowers growing in such a fashion that the outermost are borne on longer pedicels than the inner, bringing all flowers up to a common level. A corymb has a flattish top with a superficial re ...

. The flower heads have white petals (ray flowers) which make the clusters resemble a head of cauliflower and bloom during July.

Taxonomy

The species was given its first scientific description in 1803 by

Carl Ludwig Willdenow Carl Ludwig Willdenow (22 August 1765 – 10 July 1812) was a German botanist, pharmacist, and plant Taxonomy (biology), taxonomist. He is considered one of the founders of phytogeography, the study of the geographic distribution of plants. ...

, however he named it as ''Solidago leucadendron'', the same name previously given by

Georg Forster Johann George Adam Forster, also known as Georg Forster (; 27 November 1754 – 10 January 1794), was a German geography, geographer, natural history, naturalist, ethnology, ethnologist, travel literature, travel writer, journalist and revol ...

to the species now known as '' Senecio leucadendron'' making it a botanical

illegitimate name ''Nomen illegitimum'' (Latin for illegitimate name) is a technical term used mainly in botany. It is usually abbreviated as ''nom. illeg.'' Although the International Code of Nomenclature for algae, fungi, and plants uses Latin terms as qualif ...

. It was then described in 1838 by

Augustin Pyramus de Candolle Augustin Pyramus (or Pyrame) de Candolle (, , ; 4 February 17789 September 1841) was a Swiss people, Swiss botany, botanist. René Louiche Desfontaines launched de Candolle's botanical career by recommending him at a herbarium. Within a couple ...

with the name ''Lachanodes leucadendron''. The same year, but slightly later,

Stephan Endlicher Stephan Friedrich Ladislaus Endlicher, also known as Endlicher István László (24 June 1804 – 28 March 1849), was an Austrian Empire, Austrian botanist, numismatist and Sinologist. He was a director of the Botanical Garden of Vienna. Biog ...

described it and named it ''Lachanodes pladaroxylon''. The genus ''Pladaroxylon'' was named by

Joseph Dalton Hooker Sir Joseph Dalton Hooker (30 June 1817 – 10 December 1911) was a British botanist and explorer in the 19th century. He was a founder of geographical botany and Charles Darwin's closest friend. For 20 years he served as director of the Ro ...

in 1870, when he moved the species to its own genus. It is placed in the tribe

in the

family. Though this is the same tribe as for the she cabbage-tree their ancestors arrived separately on the island rather than evolving from a common ancestor in their common habitat.

Names

In English the species is commonly known as the "he cabbage-tree", though in 1775 the trees were called the "greater-cabbage-tree" by the inhabitants of the island.

Range and habitat

The species is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the Island of Saint Helena. On the island it was only found on the central ridge from 720 to 800 meters. only 55 mature individuals were known to survive in the wild.

Ecology

The he cabbage-tree is a short lived tree that grows quickly to take advantage of openings in the forest canopy. Due to competition from introduced plants such as

bilberry Bilberries () are Eurasian low-growing shrubs in the genus ''Vaccinium'' in the flowering plant family Ericaceae that bear edible, dark blue berries. They resemble but are distinct from North American blueberries. The species most often referre ...

, red cinchona, and New Zealand flax (''

Phormium tenax ''Phormium tenax'' (called flax in New Zealand English; in Māori language, Māori; New Zealand flax outside New Zealand; and New Zealand hemp in historical nautical contexts) is an evergreen perennial plant native to New Zealand and Norfolk I ...

'') it depends on human intervention to make spaces for it to survive. Formerly it formed a part of the native forest and grew at lower elevations than the other species called cabbage trees on the island. Conservation efforts for the he cabbage-tree include the planting of more than 100 seedlings to

Diana's Peak Diana's Peak is the highest point, at , on the island of Saint Helena, a British overseas territory in the South Atlantic Ocean. It is of volcanic origin. The mountain and its surroundings with a total area of 81 ha were proclaimed a national ...

National Park, but in 2012 none of the young plants were large enough to reproduce. The very low viability of the tree's seeds hamper efforts at repopulating the species.

References

External links

* {{Taxonbar, from1=Q7200435, from2=Q5489134 Senecioneae Monotypic Asteraceae genera Flora of Saint Helena Critically endangered plants