Arenga (genus)
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Labill. |
Arenga is a genus of palm native to Southeast Asia and Australia. The sugar palm ( Arenga pinnata )is of regional economic importance. Most species only bloom once.
features
The representatives are small to massive, single or multi-stemmed pinnate palms. They are predominantly monocial , more rarely diocial . Most species bloom only once, so they are hapaxanth , few species bloom several times. The trunk has short or long internodes , which are usually covered by the fibrous leaf bases and leaf sheaths. The trunk is rarely free, then it is conspicuously curled with leaf scars.
The chromosome number is 2n = 32, one species is tetraploid with 2n = 64.
leaves
The leaves are fan-shaped and induplicate (small leaflets are V-shaped in cross section) ribbed, or induplicate oddly pinnate. The leaves dry up on the palm; they rarely fall off due to their own weight. The leaf sheath is covered with various scales and hairs and often extends beyond the base of the stalk in the form of a ligula . The vagina breaks down into a mass of black fibers over time. The petiole is usually well developed. The leaflets are simply folded with the exception of the terminal one. They stand regularly or in groups and are on several levels. The upper side is usually bald or bald, the underside densely hairy and covered with brown scales.
Inflorescences
The inflorescence stands between the leaves (intrafoliar), rarely under the leaves (infrafoliar). Often it breaks through the leaf sheaths. In the multiple-blooming species, the inflorescences are formed in an acropetal sequence: from bottom to top. In the hapaxanthic species they are formed basipetally: from top to bottom. The most distal inflorescences are mostly in strongly reduced bracts . The inflorescences are bisexual. You can also be unisexual due to sterility of one gender. Then the females stand distally compared to the males. The inflorescences are usually branched one to two times.
The inflorescence stalk is short to clearly developed and has a rather inconspicuous, basal, double- keeled cover sheet and several conspicuous, spiral bracts . The bracts on the inflorescence axis are inconspicuous and triangular. The side axes that carry the flowers (rachillae) are upright or drooping, can be very slender or massive. The flower triads are located on them in a spiral arrangement.
blossoms
The male flowers open in bisexual inflorescences before the female ones. They have three rounded, leathery sepals . The crown is tubular at the base and has three oval to elongated, leathery lobes. Usually much more than 15 stamens are formed, rarely only 6 to 9. The stamens are short, the anthers long. The connective sometimes ends in a point. There is no rudiment of stamps. The pollen is ellipsoidal and rather bisymmetrical. The germ opening is a distal sulcus . The longest axis measures 27 to 36 microns.
The female flowers are usually spherical, sometimes quite large. The three sepals are rounded and leathery. The three petals are fused about halfway at the base, the end lobes are triangular. There are zero to three staminodes . The ovary is spherical, triple and has two to three scars . There are two to three fertile compartments, the ovules are semianatropic.
Fruits and seeds
The fruit is spherical to ellipsoidal , often slightly angular. It contains one to three seeds. The scar remains are apical. The exocarp is smooth and dull to light colored. The mesocarp is fleshy and has numerous irritating crystal needles. The endocarp is not differentiated. The seeds are basal, smooth and have a homogeneous endosperm .
Distribution and locations
The distribution area of the genus extends from South India, South China, the Ryukyu Islands and Taiwan over all of Southeast Asia, Malesia and Christmas Island to North Australia. Most species grow in primary forests in the lowlands and the hills of the perhumid tropics. Some species are tall palm trees that grow in clusters and form large amounts of fall foliage. They have a significant effect on forest dynamics. Smaller species, which were previously placed in the genus Didymosperma , are species of the forest understory.
Systematics
The genus Arenga Labill. ex DC. is placed within the family Arecaceae in the subfamily Coryphoideae , tribe Caryoteae . The genus is monophyletic . Her sister group is Wallichia .
The Royal Botanic Gardens, Kew's World Checklist of Selected Plant Families recognizes the following species:
- Arenga australasica (H.Wendl. & Drude) STBlake ex HEMoore : It is native to northern and northeastern Queensland .
- Arenga brevipes Becc. : The homeland is Sumatra and Borneo.
- Arenga caudata (Lour.) HEMoore : The home is Thailand, Myanmar, Malaysia, Cambodia, Laos, Vietnam and China.
- Arenga distincta Mogea : The home is Borneo.
- Arenga engleri Becc. : The home is western Taiwan.
- Arenga hastata (Becc.) Whitmore : Home is Thailand, Malaysia, Borneo and Sumatra.
- Arenga hookeriana (Becc.) Whitmore : Home is Thailand and Malaysia.
- Arenga listeri Becc. : Home is Christmas Island .
- Arenga longicarpa C.F.Wei : The home is Guangdong in China.
- Arenga longipes Mogea : The home is Sumatra.
- Arenga micrantha C.F.Wei : The range extends from southeastern Tibet to the eastern Himalayas.
- Arenga microcarpa Becc. : The homeland is Maluku , New Guinea and Australia.
- Arenga mindorensis Becc. : The home is Mindoro from the Philippines.
- Arenga obtusifolia Mart. : The home is Thailand and western Malesia.
- Arenga pinnata (worm) Merr. : The distribution area extends from Assam to Malesia.
- Arenga plicata Mogea : Home is Sumatra.
- Arenga porphyrocarpa (Blume ex Mart.) HEMoore : The distribution area extends from Sumatra to Java.
- Arenga retroflorescens H.E. Moore & Meijer : The home is Sabah on Borneo.
- Arenga ryukyuensis A.J.Hend. : The home is the Nansei Islands .
- Arenga talamauensis Mogea : Home is Sumatra.
- Arenga tremula (Blanco) Becc. : The home is the Philippines.
- Arenga undulatifolia Becc. : The home is Borneo, Sulawesi and Palawan from the Philippines.
- Arenga westerhoutii handle. : The distribution area extends from Bhutan to southern China and Malaysia.
- Arenga wightii handle. : The home is southwest India.
Fossil history
An inflorescence stem from India, Palmostroboxylon arengoidum , was placed near Arenga . One seed, Iriartea collazoensis , from the mid Oligocene of Puerto Rico, closely resembles those of Arenga and Iriartea . The pollen genus Arengapollenites comes from the lower Eocene of India and is very similar to that of Arenga .
supporting documents
- John Dransfield, Natalie W. Uhl, Conny B. Asmussen, William J. Baker, Madeline M. Harley, Carl E. Lewis: Genera Palmarum. The Evolution and Classification of Palms . Second edition, Royal Botanic Gardens, Kew 2008, ISBN 978-1-84246-182-2 , pp. 300-303.
Individual evidence
- ↑ Rafaël Govaerts (ed.): Arenga. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved November 20, 2009.
Web links
- Arenga on the homepage of the Fairchild Tropical Botanic Garden