Kentia palms
| Kentia palms | ||||||||||||
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Howea forsteriana |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Howea | ||||||||||||
| Becc. |
The Kentia palms ( Howea ) are a genus of the palm family endemic to the Australian Lord Howe Island . Both types are very common ornamental plants.
features
The representatives are medium-sized, single-stemmed, unreinforced palms. They are the largest palms within the Laccospadicinae subtribe . They are single sexed ( monoecious ) and flowering several times (pleonanth). The trunk is upright, glabrous and covered with clearly tight-fitting, horizontal or inconspicuous leaf scars . The base of the trunk is sometimes thickened.
The chromosome number is 2n = 32.
leaves
The leaves are pinnate. They do not form a crown shaft. After they die, they fall cleanly from the trunk. The leaf sheath is well developed, tears open lengthways opposite the petiole, and later disintegrates into an intertwined mass of fine fibers. The petiole is short to moderately long. It is flattened or slightly furrowed on top. It is angular on the underside. It is barely or densely covered with scales. The rachis is rounded to angular on the underside, angular on the upper side and scales like the stem.
The leaflets are numerous, simply folded and arranged regularly. They stand up arched or stiff. The end is pointed or slightly two-pointed (bifid). The top is scattered with scales, the underside is covered with dense flaky hair.
Inflorescences
The inflorescences are inside the crown, but can also be below the leaf crown due to leaf fall. They are short to about the same length as the leaves. They are spike-shaped and stand individually or in groups of 3 to 8 inflorescences. They initially stand upright and are later hanging down. The inflorescences are proterandric . The inflorescence stalk is elliptical in cross section and much shorter than or about the same length as the inflorescence axis . The cover sheet is tubular, membranous, and later tears open lengthways, disintegrates or falls off, and leaves a low collar. The inflorescence axis is robust, scaly hairy. There are low, round or triangular, stiff, cartilaginous bracts tightly packed in a spiral arrangement . Each forms the lip of a flower pit in which there is a flower triad. Only at the tip of the inflorescence do they contain only one male pair of flowers.
blossoms
The male flowers only partially reach out of the flower pit during flowering. The three sepals are free, imbricat , and mostly keeled. They are rounded and the edges are serrated. The crown had a stem-like base and is about as long as the calyx. It has three oval, valvate lobes. There are 30 to 70 or more stamens , their filaments are long and fused to different extents at the base. The connective are sometimes elongated to a point. The anthers are elongated, more or less lantrors. A pestle lode is missing. The pollen is ellipsoidal, asymmetrical to pear-shaped. The germ opening is a distal sulcus. The longest axis with 37 to 52 µm.
The female flowers are approximately spherical. The three sepals are free, imbricat, rounded and toothed on the edges. The three petals are free, strongly imbricated at the base, the tips valvated for short. There are 3 to 6 staminodes that form a low, irregularly lobed, membranous ring, or they are irregularly separated and triangular or bilobed. The gynoeceum is single-compartment with an ovule . It has three short stigmas that curve back to the flower. The ovule is attached laterally and is kampylotropic.
fruit
The fruit is egg-shaped. It contains a seed. It is glossy dark green at the beginning and later becomes dull yellowish green or reddish brown. The petals remain on the fruit, the scar remains on the fruit. The exocarp is smooth, the mesocarp is rather thin, fleshy and with numerous longitudinal fibers. The endocarp is cartilaginous and not attached to the semen. The seed sits on the side. The raphe reaches more than a third of the seed at most. The endosperm is homogeneous. The embryo is basal.
Distribution and ecology
The two species are endemic to Lord Howe Island . They come from the lowland forests up to 450 m above sea level. They are quite common on the island and occur in 70% of the vegetation.
The most important pollination mechanism in both species is the wind , one of the few cases where this has been clearly demonstrated in palm trees. Flowers and fruits ripen quite slowly, so that several inflorescences in different stages can often be found on a palm.
Systematics
The genus Howea is placed within the family Arecaceae in the subfamily Arecoideae , Tribus Areceae and Subtribus Laccospadicinae . The genus is monophyletic . It is the sister group of Laccospadix . The two genera separated from each other 4.57 to 5.53 million years ago.
In the World Checklist of Selected Plant Families of the Royal Botanic Gardens, Kew , the following types are recognized:
- Howea belmoreana (C.Moore & F.Muell.) Becc. : It grows on Lord Howe Island scattered between Howea forsteriana , but is more common at higher altitudes up to 450 m.
- Howea forsteriana (F. Muell.) Becc. : It is widespread in the lowland forest on sandy soil on Lord Howe Island.
The genus was first described by Odoardo Beccari in 1877 . The lectotype is Howea belmoreana . The name refers to the home island of the two species, the name of which goes back to Admiral Lord Richard Howe .
Both species occur at least partially in the same locations, but extremely few hybrids have been found. The two species only separated from each other after the creation of Lord Howe Island. The two species are reproductively isolated from each other. They are considered an example of sympatric speciation .
literature
- 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. 562-564.
Web links
Individual evidence
- ^ A b c d 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. 562-564.
- ↑ a b c Vincent Savolainen, Marie-Charlotte Anstett, Christian Lexer, Ian Hutton, James J. Clarkson, Maria V. Norup, Martyn P. Powell, David Springate, Nicolas Salamin, William J. Baker: Sympatric speciation in palms on an oceanic island . Science, 2006, Volume 441, pp. 210-213. doi : 10.1038 / nature04566 ; (PDF, 291 kB) ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ Rafaël Govaerts (ed.): Howea. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved August 7, 2018.
