monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
in the
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Cucurbitaceae
The Cucurbitaceae, also called cucurbits or the gourd family, are a plant family consisting of about 965 species in around 95 genera, of which the most important to humans are:
*''Cucurbita'' – squash, pumpkin, zucchini, some gourds
*''Lagena ...
. The only species is ''Dendrosicyos socotranus'', the cucumber tree. The species is
endemic
Endemism is the state of a species being found 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 found elsew ...
to the island of
Socotra
Socotra or Soqotra (; ar, سُقُطْرَىٰ ; so, Suqadara) is an island of the Republic of Yemen in the Indian Ocean, under the ''de facto'' control of the UAE-backed Southern Transitional Council, a secessionist participant in Yemen’s ...
in
Yemen
Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the Saudi Arabia–Yemen border, north and ...
, and is the only species in the Cucurbitaceae to grow in a tree form. The species name was originally spelled ''D. socotrana'', but this is corrected to masculine
grammatical gender
In linguistics, grammatical gender system is a specific form of noun class system, where nouns are assigned with gender categories that are often not related to their real-world qualities. In languages with grammatical gender, most or all nouns ...
according to the
International Code of Nomenclature for algae, fungi, and plants
The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all those "trad ...
.
Features
It has a bulbous trunk and a small crown. It was first described by
Isaac Bayley Balfour
Sir Isaac Bayley Balfour, KBE, FRS, FRSE (31 March 1853 – 30 November 1922) was a Scottish botanist. He was Regius Professor of Botany at the University of Glasgow from 1879 to 1885, Sherardian Professor of Botany at the University of Oxfor ...
in 1882. 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.
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
Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature res ...
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.
''D. socotranus'' has a bottle-shaped base of fibrous wood (
pachycaul
Pachycauls are plants with a disproportionately thick Trunk (botany), trunk for their height, and few branches. This can be the product of exceptional primary growth (as with Arecaceae, palms and cycads) or disproportioate secondary growth as with ...
). 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
Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms.
Etymology
The term ''parenchyma'' is New Latin from the word π ...
. In it are embedded small
xylem
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
strands that are linked to each other (
anastomosis
An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf#Veins, leaf veins, or streams. Such a connection m ...
). These xylem strands have a
cambium
A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from w ...
, and a secondary
phloem
Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...
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 25 cm 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
flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...
s occur in the leaf axils. The species is
monoecious
Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy.
Monoecy is conne ...
- male and female flowers on one plant. The flowers are yellowish-orange with long petals and the fruits are ovate. The seeds are about 6 mm.
The plant contains dendrosycin, an iso-
cucurbitacin
Cucurbitacin is a class of biochemical compounds that some plants – notably members of the pumpkin and gourd family, Cucurbitaceae – produce and which function as a defence against herbivores. Cucurbitacins are chemically classified as trit ...
with an unusual ring formation.
Proliferation and locations
Described in 1882 by
Isaac Bayley Balfour
Sir Isaac Bayley Balfour, KBE, FRS, FRSE (31 March 1853 – 30 November 1922) was a Scottish botanist. He was Regius Professor of Botany at the University of Glasgow from 1879 to 1885, Sherardian Professor of Botany at the University of Oxfor ...
, 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
Djibouti, ar, جيبوتي ', french: link=no, Djibouti, so, Jabuuti officially the Republic of Djibouti, is a country in the Horn of Africa, bordered by Somalia to the south, Ethiopia to the southwest, Eritrea in the north, and the Red ...
. It is quite abundant on the dry parts of the island of
Socotra
Socotra or Soqotra (; ar, سُقُطْرَىٰ ; so, Suqadara) is an island of the Republic of Yemen in the Indian Ocean, under the ''de facto'' control of the UAE-backed Southern Transitional Council, a secessionist participant in Yemen’s ...
, associated with '' Croton socotranus'' in the plains, and on calcareous soils to 500 m elevation. The species is well-adapted to dry sites. It is widely distributed in several vegetation types but has a rather fragmented distribution; over large areas there are only isolated trees or small relict populations, whilst in other areas it is relatively abundant. There are a few trees on the island of
Samhah
Samhah or Samha ( ar, سمحة) is an inhabited island in the Guardafui Channel. A part of the Socotra archipelago, it is located between the island of Socotra and Somalia. Like the whole group, it belongs to Yemen and is part of Socotra Governora ...
, but none on
Darsah
Darsah ( ar, درسة) is an uninhabited island in the Guardafui Channel. It is part of the Socotra Archipelago of Yemen. Darsah and neighboring Samhah ( to the west) are collectively known as "Al Akhawain" ( ar, الأخوين) which means "The B ...
or
Abd al Kuri
Abd al Kuri ( ar, عبد الكوري) is a rocky island in the Guardafui Channel. As a part of the Socotra Archipelago of the Socotra Governorate of Yemen, it lies about 65 miles (105 km) southwest of the island of Socotra.Lycium sokotranum'' or by colonies of the succulent shrub '' Cissus subaphylla''. Where there is no ''Cissus'' or ''Lycium'', there is little if any regeneration. Thus, along the southern region of Socotra and on Samhah the recovery of populations of ''Dendrosicyos'' after drought is dependent on the presence of colonies of ''Cissus''.
Nomenclature
The genus is in the pumpkin subfamily Cucurbitoideae and in the
tribe
The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English language, English is in the discipline of anthropology. This definition is contested, in p ...
Coniandreae. ''Dendrosicyos'' is the basal taxon within the tribe, all other genera of the tribe being a
sister group
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and t ...
.Kocyan Alexander, Li-Bing Zhang, Hanno Schaefer, Susanne S. Renner. A multi-locus chloroplast phylogeny for the Cucurbitaceae and its implications for character evolution and classification. ''Molecular Phylogenetics and Evolution'', Volume 44(2), August 2007, pp. 553-577 doi:10.1016/j.ympev.2006.12.022
The name ''Dendrosicyos socotranus'' means 'cucumber tree of Socotra'.