| Dendrosicyos | |
|---|---|
| An 1890s photograph by Henry Ogg Forbes | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Rosids |
| Order: | Cucurbitales |
| Family: | Cucurbitaceae |
| Subfamily: | Cucurbitoideae |
| Tribe: | Melothrieae |
| Subtribe: | Dendrosicyinae |
| Genus: | Dendrosicyos Balf.f. |
| Species: | D. socotranus |
| Binomial name | |
| Dendrosicyos socotranus Balf.f. |
|
Dendrosicyos is a monotypic genus in the 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.
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It has a bulbous trunk and a small crown.[1] It was first described by Isaac Bayley Balfour in 1882.[2] 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 relict of a progenitor lineage that went extinct on the mainland.[3]
It measures up to 6 m high, and 2 m in diameter. 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 vulnerable. In Soqotri, its name is qamhiyn.
Contrary to what its region of origin would suggest, Dendrosicyos socotrana responds well to a drench and fertilizer, if the temperature is greater than 20 °C. Individuals in their natural habitat can attain 10 feet/3 m in height. The plants grow relatively fast, but do not get taller than a meter. Trunks are succulent, but not bottle-shaped when young. The plant produces flowers when five years old. [4]
Dendrosicyos socotranus will grow to 7 m and has a bottle-shaped base of fibrous wood (Pachycaulie). 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.
The base consists largely of parenchyma. In it are embedded small xylem strands that are linked to each other (anastomosis). These xylem strands have a cambium, and a secondary phloem forms. There is not a consistently active cambium - it will always be sequentially formed on the periphery of a new cambium (cambium successively). Dendrosicyos is the first member of the Cucurbitaceae, in which such meristem has been demonstrated.
The leaves are about 10 inches long and wide, its leaf edge being slightly thorny. On the underside of the leaves are trichomes of from two to seven cells, the cells often containing two cystoliths. The epidermal cells are lignified, the surface carries a thick cells however secrete.
The flowers occur in the leaf axils. The species is monoecious - male and female flowers on one plant. The flowers are yellowish-orange with long petals, while the fruits are ovate and jump on to maturity. The seeds are about 6 mm.
The plant contains Dendrosycin, an iso-cucurbitacin with an unusual ring formation. [5]
Described in 1882 by Isaac Bayley Balfour, the species is generally described as endemic to the island of Socotra, although some sources (1887) state that it was present on the African continent in Djibouti. It is quite abundant on the dry parts of the island of Socotra, associated with Croton socotranus in the plains, and on calcareous soils to 500 m elevation. There are also isolated specimens on the close island of Samhah. Dendrosicyos socotranus is only on the island of Socotra, an island off the Horn of Africa. The species is well adapted to dry sites.
The genus is in the pumpkin subfamily Cucurbitoideae and in the Tribe Coniandreae. Dendrosicyos is the basal taxon within the tribe, all other genera of the tribe being a sister group. [6]
The name 'Dendrosicyos socotranus' means 'cucumber tree of Socotra'.