Ravenea
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Ravenea is a genus of palm trees and occurs only in Madagascar and the Comoros . The genus is named after Louis Ravené from Berlin.
features
From habit , the representatives of the genus are highly variable. Some species like Ravenea hildebrandtii already bloom to a height of one meter. Ravenea robustior reaches heights of growth of 25 m, its trunk can reach a diameter of one meter in the extended central part. The basal part of the trunk is swollen and can be three times the diameter of the rest of the trunk.
The leaves protrude slightly upwards and form a shuttlecock-like crown, sometimes the leaves are also bent in an arch. In some species, the dead leaves remain on the plant and form a dense layer around the upper part of the trunk, such as Ravenea louvelii and Ravenea xerophila .
With the exception of Ravenea musicalis , all species have a layer of dense, very hard longitudinal fibers in the outer area of the trunk, which contribute to the hardness of the trunk. The tribes of Ravenea lakatra are so harsh that their name means Cannot be felled even by an army in the Manombo area .
leaves
The leaves are arranged in a spiral in all species. The number of leaves ranges from 6 to 28. In a few species, the remnants of the leaf sheaths remain on the trunk, in most species the trunk is free of sheath remnants and the old leaves fall off smoothly. The transition from the leaf sheath to the petiole is indistinct. Young sheaths are initially closed and are then torn open by the leaves that are formed later. They disintegrate and gradually disappear. Clearly recognizable ears are missing. From the sheath mostly only stiff fibers pointing downwards remain on the side opposite the petiole. The petiole is usually furrowed on the top and sometimes has sharp edges. At the rachis , the lower leaflets start at the edge, further up they start in narrow channels at the edge of the rachis.
The leaflets are numerous and regularly arranged. The leaflets on one side of the rhachis are always in one plane. The leaflets are almost always bare, some are covered with a thin layer of wax. Only in Ravenea albicans is the underside of the leaflets hairy white.
Inflorescence and flowers
The species are diocesan , male and female inflorescences are on different individuals. The inflorescence is always between the leaves. There are single and multiple inflorescences: in seven species the male inflorescences are multiple inflorescences, female there are only in Ravenea madagascariensis . These are false multiple inflorescences, in which the axes of the inflorescences arise in the axilla of a single cover leaf . The inflorescence is branched one or two times.
The flowers are open from the earliest observable developmental stage, long before the inflorescence opens. In some of the species, the stamens are arranged in two rows in the male flower : a group of three in front of the sepals is inserted at the base of the flower, the others in front of the petals are partially fused with them. In some of these species, in turn, the petals are connected to each other by a callus- like filament of the stamens in front of the sepals.
fruit
The remnants of the scar vary greatly in terms of their location on the fruit: from apical to sub-basal, also subapical or laterally. The color of the fruit ranges from yellow to orange and red to dark purple and black. In dark fruits there is a sclerotic endocarp around the single to three seeds . The mesocarp of most fruits is fleshy. Only in Ravenea musicalis is it spongy, which means that the fruits float in the water.
The smallest fruits are those of Ravenea rivularis with a diameter of 7 to 9 mm (seeds 5 to 6 mm). Ravenea krociana , which grows in the rainforest, has 25 to 30 mm large fruits.
ecology
Pollination and mechanisms of spread are practically completely unknown. Bees and beetles are known to visit flowers. In Ravenea dransfieldii the flowers give off a thick, smelly odor. The fruits of most species are fleshy and colorful. Spread by birds or lemurs would be possible . The fruits of Ravenea musicalis are pretty sure to spread from the water. They swim, and the seeds are already germinating in the floating, closed fruit.
The flowering times are also hardly known, most species should bloom between August and October, the fruits ripen from the beginning of the year to March.
Distribution and locations
The genus Ravenea occurs only in Madagascar and the Comoros. It inhabits a variety of locations from dry bushland to lowland rainforests and heather heathland in the mountains. One species grows in the water.
Systematics
Ravenea H. Wendl. ex CDBouché is classified within the family in the subfamily Ceroxyloideae, tribe Ceroxyleae. In his monograph on the genus, Henk Jaap Beentje assigned the species of the genus Louvenia to Ravenea . He differentiates 17 types; there are now other species:
- Ravenea albicans (Jum.) Beentje : Home is north-eastern Madagascar.
- Ravenea beentjei Rakotoarin. & J.Dransf. : The home of this species, which was only newly described in 2010, is Madagascar.
- Ravenea declivium J. Transf . & Rakotoarin. : The species first described in 2012 occurs in Madagascar.
- Ravenea delicatula Rakotoarin. : The home of this species, which was first described in 2008, is Madagascar.
- Ravenea dransfieldii Beentje : The home is eastern Madagascar.
- Ravenea glauca Jum. & H.Perrier : The home is southern and central Madagascar.
- Ravenea hildebrandtii H. Wendl. ex CDBouché : Home is the Comoros .
- Ravenea hypoleuca rakotoarin. & J.Dransf. : The home of this species, which was only newly described in 2010, is Madagascar.
- Ravenea julietiae Beentje : The home is eastern Madagascar.
- Ravenea krociana Beentje : The homeland is south-eastern Madagascar.
- Ravenea lakatra (Jum.) Beentje : The homeland is eastern Madagascar.
- Ravenea latisecta Jum. : The homeland is eastern and central Madagascar.
- Ravenea louvelii Beentje : The home is eastern and central Madagascar.
- Ravenea madagascariensis Becc. : The home is central and southeastern Madagascar.
- Ravenea moorei J.Dransf. & NWUhl : The home is Grande Comore , the main island of the Comoros.
- Ravenea musicalis Beentje : The home is south-eastern Madagascar.
- Ravenea nana Beentje : The homeland is northern and southeastern Madagascar.
- Ravenea rivularis Jum. & H.Perrier : The home is southwest Madagascar.
- Ravenea robustior Jum. & H.Perrier : The home is northern and eastern Madagascar.
- Ravenea sambiranensis Jum. & H.Perrier : The home is Madagascar.
- Ravenea xerophila Jum. : The home is southern Madagascar.
use
Some species are of local economic importance. The outer wood of some types is used for wooden floors and tables. The wood appears to be termite- resistant. The palm heart of some species is eaten: Ravenea albicans, robustior, and sambiranensis . Hats are made from the leaflets. The hollowed out stems of Ravenea julietiae are used as water pipes in irrigation. The seeds of Ravenea rivularis are traded because the species has some horticultural importance.
supporting documents
- HJ Beentje: A monograph of Ravenea (Palmae: Ceroxyloideae) . Kew Bulletin, Vol. 49, 1994, pp. 623-671.
Individual evidence
- ^ 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 , p. 343.
- ↑ a b c d e f Rafaël Govaerts (Ed.): Ravenea. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved August 4, 2018.
