Dendrosicyos is a monotypic genus in the plant family Cucurbitaceae. The only species is Dendrosicyos socotranus, the cucumber tree. The species is endemic to the island of Socotra in Yemen, and is the only species in the Cucurbitaceae to grow in a tree form. The species name was originally spelled D. socotrana,[2] but this is corrected to masculine grammatical gender according to the International Code of Nomenclature for algae, fungi, and plants.[3][4]
It has a bulbous trunk and a small crown.[5] It was first described by Isaac Bayley Balfour in 1882.[1] A recent molecular phylogenetic analysis of the family Cucurbitaceae found that the Dendrosicyos lineage is about twice as old as the island, and thus seems to be an island relic of a progenitor lineage that became extinct on the mainland.[6]
The leaves are nearly round, covered with fine bristles, and slightly toothed. The yellow flowers (3 cm), males and females are present on the same plant for cross pollination. It reproduces only by seed. Fruits (3 x 5 cm) are green, turning brick-red when ripe.
Seedlings subjected to overgrazing and regeneration may be compromised over time, except for seedlings protected from goats by Cissus subaphylla. The species is considered endangered. In Soqotri, its name is qamhiyn.
Contrary to what its region of origin would suggest, Dendrosicyos socotranus responds well to a being drenched and fertilized, if the temperature is greater than 20 °C. Individuals in their natural habitat can attain 3 meters (10 feet) in height. Trunks are succulent, but not bottle-shaped when young. The plant produces flowers when five years old.[7]
D. socotranus has a bottle-shaped base of fibrous wood (pachycaul). The trunk reaches a diameter of up to one meter. Numerous small twigs and branches grow from the stem, the bottle tree growth form making it distinctive.