Alfalfa arbórea
This species belongs to the legume family and was described by Pío Font Quer in 1924, based on specimens collected from the island of L'Espartar, off the coast of Ibiza. Although initially classified as a variety of Medicago arborea, a species widespread throughout the Mediterranean, it was later recognized as a distinct species endemic to the Spanish Levant.
Distribution
It is endemic to the small islands of the Columbretes archipelago, off the city of Castellón, as well as the surrounding islets near Ibiza and Cabrera in the Balearic Islands. It also found on a small islet off the coast of Alicante, near Cape San Antonio.
Habitat
This species occurs between 10 and 50 metres above sea level, growing in crevices in coastal limestone rocks. It can colonise coastal cliffs and soils that are nitrified and brackish. Its restriction to small islands is likely due to herbivory by goats, rats and rabbits on the larger islands. Flowering occurs from December to May, with fruiting in the summer months. Seed dispersal is believed to be facilitated by birds and other animals that consume the fruits.
Conservation
There are 12 known natural populations and two reintroduced populations that have recovered from local extinction. The total population is estimated at around 2,500 individuals, although a precise and up-to-date census is lacking. Major threats include the introduction of herbivores, particularly rats and rabbits, as well as infestations by the cottony cushion scale (a mealybug pest). Parasitic plants and invasive species also pose significant risk.
Conservation efforts include seed preservation in multiple germplasm banks and close monitoring of populations in the Cabrera National Park, alongside the implementation of biological control measures for the mealybug. On the island of S'Espartar, rabbit population control has led to a recovery of Medicago citrina in areas previously affected by herbivory.
Images descriptions
The scanning electron microscope image shows a complete, elongated and reniform seed. The surface is smooth with slight undulations and is covered by a hard outer layer called the testa. A shallow depression marks the location of the hilum, the scar where the ovule attaches the ovary wall.