Euphorbia herbstii is a rare species of flowering plant in the euphorb family

Euphorbiaceae

Euphorbiaceae, the Spurge family are a large family of flowering plants with 300 genera and around 7,500 species. Most are herbs, but some, especially in the tropics, are also shrubs or trees. Some are succulent and resemble cacti....

 known by the common name Herbst's sandmat. It is endemic to Oahu

Oahu

Oahu or Oahu , known as "The Gathering Place", is the third largest of the Hawaiian Islands and most populous of the islands in the U.S. state of Hawaii. The state capital Honolulu is located on the southeast coast...

, Hawaii

Hawaii

Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

, where it is rapidly disappearing. Like other Hawaiian euphorbs, this plant is known locally as akoko. It is a federally listed endangered species

Endangered species

An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

 of the United States.

This plant is usually a tree

Tree

A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

 which can grow up to 8 meters tall. The leaf blades are long and narrow, and the branches bleed a milky sap

Sap

Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...

. The inflorescence

Inflorescence

An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...

 is a cluster of cyathia

Cyathium

A cyathium is one of the specialised pseudanthia forming the inflorescence of plants in the genus Euphorbia . A cyathium consists of:...

.

This species is known from perhaps four populations in mesic forests on the Waianae Range

Waianae Range

Waianae Range is the eroded remains of an ancient shield volcano that comprises the western half of the Hawaiian Island of Oahu...

. Since the year 2000 the plant has undergone a severe decline, with populations extirpated

Local extinction

Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...

 and remaining ones becoming smaller. The exact number of remaining plants is unknown because each survey tallies fewer individuals, while more have been planted in appropriate habitat.

Threats to the species include feral pigs, which uproot and trample vegetation, leading to loss of plant cover and root networks, which then leads to erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

. They pick up the seeds of invasive plant species

Invasive species

"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

 and transport them to new habitats. Fence

Fence

A fence is a freestanding structure designed to restrict or prevent movement across a boundary. It is generally distinguished from a wall by the lightness of its construction: a wall is usually restricted to such barriers made from solid brick or concrete, blocking vision as well as passage .Fences...

s have been erected in critical areas to exclude the pigs. Non-native plants

Introduced species

An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...

 affecting the euphorb include silky oak

Grevillea robusta

Grevillea robusta, commonly known as the southern silky oak or Silky-oak, or Australian Silver-oak, is the largest species in the genus Grevillea. It is a native of eastern coastal Australia, in riverine, subtropical and dry rainforest environments receiving more than 1,000 mm per year of...

 (Grevillea robusta), corky-stem passionflower

Passiflora suberosa

Passiflora suberosa is a species of passion flower that is native to the Americas. Its range stretches from Florida and the Lower Rio Grande Valley of Texas in the United States south through Mexico, Central America, and the Caribbean to South America. It is commonly known as Corky-stemmed Passion...

 (Passiflora suberosa), and strawberry guava (Psidium littorale).