Borasseae

Borasseae is a tribe in the palm subfamily Coryphoideae. The tribe ranges from southern Africa and Madagascar north through the Arabian Peninsula to India, Indochina, Indonesia and New Guinea. Several genera are restricted to islands in the Indian Ocean. The two largest genera, ''Hyphaene'' and ''Borassus'', are also the most widespread.

Description

Borassoid palms typically have large, column-like trunks, though several species of ''Hyphaene'' have branching or clustered stems. The leaves are large, palmate and often with spines or sharp edges along the petioles. Leaves are retained on young palm stems, later falling to reveal prominent scars. All genera in the Borasseae are dioecious, with separate male and female trees; they are pleonanthic, flowering regularly for many years. Inflorescences are large and pendulous; the male flowers are much smaller than the female and are borne in clusters within catkin-like structures. Fruits contain hard, woody endocarps surrounding the seeds; they range in size from date-sized (''Latania'') to the massive fruits of ''Lodoicea'', which contain the largest seed in the world.

Taxonomy

The Borasseae is one of eight tribes in subfamily Coryphoideae. The tribe is monophyletic and most phylogenetic studies place it as sister to tribe Corypheae, though it is also close to tribe Caryoteae and tribe Chuniophoeniceae. Together, the four tribes make up the syncarpous clade, all members of which have syncarpous ovaries with united carpels.

The eight genera of tribe Borasseae split evenly into two subtribes. In the palms of subtribe Hyphaenieae, both the male and female flowers are sunken within pits and the fruits are stalked and typically one-seeded. ''Bismarckia'' (1 sp., ''B. nobilis'') and ''Satranala'' (1 sp., ''S. decussilvae'') are endemic to Madagascar, '' Medemia'' (1 sp., ''M. argun'') is restricted to Egypt and Sudan, while ''Hyphaene'' (8 spp.) ranges from southern Africa and Madagascar to western India. In subtribe Lataniieae, only the male flowers are sunken in pits and the fruits are sessile, with 1-3 seeds. ''Lodoicea'' (1 sp., ''L. maldivica'') is endemic to the Seychelles, ''Latania'' (3 spp.) is endemic to the Mascarene Islands, while ''Borassodendron'' has two species, one in Borneo ( ''B. borneense'') and one in the Malay Peninsula ('' B. machadonis''). The last of the genera, ''Borassus'' (5 spp.), is the most widespread and is found in Sub-Saharan Africa, Madagascar, Southeast Asia and New Guinea. An extinct genus of the subtribe Hyphaeninae is known from the Maastrichtian aged Intertrappean Beds of India.

Conservation

Many species in tribe Borasseae are threatened with extinction (36% of total recognized species):
* '' Borassodendron machadonis'' - Vulnerable
* '' Borassus madagascariensis'' - Endangered
* ''Latania loddigesii'' - Endangered
* ''Latania lontaroides'' - Endangered
* ''Latania verschaffeltii'' - Endangered
* '' Lodoicea maldivica'' - Endangered
* ''Medemia argun'' - Critically Endangered
* '' Satranala decussilvae'' - Endangered

Gallery

File:Latania loddigesii 6zz.jpg, Female flowers of ''Latania loddigesii''
File:Coco de mer - male.jpg, Male flowers of ''Lodoicea maldivica''
File:Coco de Mer male inflorescence.JPG, Male flowers of ''Lodoicea maldivica'' emerging from catkin-like inflorescence
File:Female nut Coco de Mer and sea foam.jpg, Seed of ''Lodoicea maldivica'', the world's largest seed
File:Latania loddigesii seeds.jpg, Seed of ''Latania'' are the smallest in the tribe
File:Doum Palm.jpg, Unlike most Borasseae, ''Hyphaene'' species often have branching stems (this is ''H. compressa'')
File:Borassus aethiopum 0033.jpg, All Borasseae have palmate leaves, as with this ''Borassus aethiopum''
File:Bismarckia nobilis palm tree growing on Sanibel Island, Florida.jpg, The silvery leaves of ''Bismarckia nobilis'' make it a popular palm in cultivation
File:Borassus aethiopum 0098.jpg, ''Borassus'' fruits are large and fleshy, with 1-3 seeds (this is ''B. aethiopum'')
File:Hyphaene petersiana01.jpg, ''Hyphaene'' fruits have a dry, cake-like flesh and a single seed (this is ''H. petersiana''
File:Lodoicea maldivica.jpg, The massive leaves of ''Lodoicea maldivica'' are some of the largest palmate leaves in the family
File:Atakora-Borassus aethiopum (3).jpg, Leaf scars on the trunk of ''Borassus aethiopum'' are revealed as the leaf sheaths fall off

References

{{Taxonbar, from=Q893320

Monocot tribes