Washingtonia

Washingtonia filifera in Joshua Tree National Park

Washingtonia is a North American genus Palm. The two types are commonly used in the dry subtropics as ornamental plants.

• 4.1 Notes and references

Features

The representatives are showy, solitary tree-shaped fan palms. They are hermaphroditic and repeatedly flowering. The stem is erect and usually partially or completely covered with the remaining dry leaves. The stem is densely covered with annular leaf scars.

The chromosome number is 2n = 36

The leaves are fan-shaped ( costapalmat ), folded induplicat and remain ( Marzeszenz ) after the death of the plant. The leaf sheath has a conspicuous abaxial column below the petiole. The edges decompose into a dark brown fibrous network. The petiole is long, on the upper side flattened to slightly concave, rounded at the bottom, the edges are reinforced with curved teeth. Towards the distal end, the teeth are smaller and are more distant. The Hastula on the bottom is large, membranous, triangular with an irregular edge, the Hastula on the bottom is a low elevation which is obscured by dense pubescence at Washingtonia robusta.

The leaf blade is divided approximately one third irregularly into segments. The segments are easily folded, linear, bifid at the tip ( two-piece), and hanging with age. The threads between the folds are conspicuous. The middle ribs are clearly at the bottom.

Inflorescences

The inflorescences are between the sheets ( interfoliar ), are ascending, curved, slim and triply branched (up to four times). They are the same length as or often longer than the leaves. The peduncle is short. The cover page is Roehrig, with tight -fitting sheath, zweikielig, irregular and torn at the top. At the peduncle there is a bract, this is similar to the previous sheet, but is einkielig. The inflorescence axis is much longer than the stem. The bracts are here Roehrig at the base, then along open. They are flat and sword similar to this cartilaginous. The following bracts are small or absent. There are numerous flower-bearing lateral axes ( Rachillae ), which are short very slender and bare.

Flowers

The flowers are hermaphroditic, are single, oblong, standing in a spiral arrangement and are short-stalked. The cup is Roehrig with three irregular, imbricaten corners; he remains on the fruit. The crown is Roehrig to a third of the length, the free tip are valvat, narrow oval, bent back in the heyday and thin. The six stamens are on the corolla tube mouth, the filaments are long and narrowing from a fleshy base. The anthers are long, Medifix, flexible and latrors. The gynoecium consists of three carpels, the free basal meaningful, connected in the long, slender pistils. The ovule is basal, erect and may anatrop.

Fruit and seeds

The fruits are small, broadly ellipsoid to globose and often fall to the fruit stalk and the calyx tube from one side torn. The fruit is blackish, the scar remains and the carpel are not developed apically. The exocarp is smooth and thin, the mesocarp is thin, fleshy with few flattened longitudinal fibers. The endocarp is thin, crusty, not connected to the seed and smooth inside.

The seed is ellipsoid, slightly compressed, with a basal, eccentric navel ( hilum ). The raphe extends over two-thirds of shiny red-brown seed coat. She's branched side. The endosperm is homogeneous. The embryo sits basal.

Dissemination

The home of Washingtonia the desert oases of the southwestern United States and northwestern Mexico. Washingtonia filifera is found in southeastern California, western Arizona and Baja California; Washingtonia robusta in Baja California and Sonora. They are desert palms along the rivers and canyons, but also with sources in open countryside.

System

The genus Washingtonia is placed in the subfamily Coryphoideae, Tribe Trachycarpeae within the family Arecaceae. However, within the tribe can not be assigned to subtribe. The monophyly of the genus has not yet been investigated.

In the World Checklist of Selected Plant Families of the Royal Botanic Gardens, Kew, the following types are recognized:

• Washingtonia filifera
• Washingtonia robusta

Washingtonia was first described by Hermann Wendland 1879, the type species Washingtonia filifera is ( Linden ex André ) H. Wendl. ( = Pritchardia filifera Linden ex André ). The genus name honors the first President of the United States, George Washington.

A synonym is Neowashingtonia Sudw.

Fossil the species is not known.

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. 285-287.