1. Family: Arecaceae Bercht. & J.Presl
    1. Washingtonia H.Wendl.

      1. This genus is accepted, and its native range is SW. U.S.A. to NW. Mexico.

    [PW]
    Biology
    Desert palms occurring along streams and canyons, also about springs and seepages in more open areas.
    Vernacular
    Washington palms, desert fan palm (Washingtonia filifera), Mexican washington (W. robusta).
    General Description
    Robust, tall, solitary, armed, pleonanthic, hermaphroditic tree palms. Stem erect, usually partly or wholly covered with persistent dry leaves, ringed with close leaf scars, sometimes enlarged basally. Leaves induplicate, costapalmate, marcescent; sheath with a conspicuous abaxial cleft below the petiole, the margins disintegrating into a dark-brown fibrous network, the sheath densely caducous tomentose, margins becoming fibrous; petiole elongate, adaxially flattened to slightly concave, abaxially rounded, margins strongly armed with curved teeth, teeth becoming smaller and sparser distally; adaxial hastula large, membranous, triangular, irregularly margined and tattering, abaxial hastula a low ridge obscured by a mat of thick tomentum (in Washingtonia robusta); blade divided irregularly to ca. 1/3 its length into linear single-fold segments, bifid at their apices, pendulous at maturity, filamentous at the tips, interfold filaments conspicuous, midribs prominent abaxially, transverse veinlets obscure. Inflorescence interfoliar, ascending, branched to 3(–4) orders, equalling or generally exceeding the leaves, curved, slender; peduncle short; prophyll tubular, closely sheathing, 2-keeled, irregularly tattered at the tip; peduncular bract 1, like the prophyll but with a single keel; rachis much longer than the peduncle; rachis bracts tubular basally, splitting longitudinally, becoming flattened and sword-like, very coriaceous; subsequent bracts minute or lacking; rachillae numerous, short, very slender, glabrous. Flowers solitary, elongate, spirally inserted, briefly pedicellate; calyx chaffy, tubular proximally with 3 irregularly tattered, imbricate lobes, persistent in fruit; corolla tubular for ca. 1/3 its length, distinct lobes valvate, narrowly ovate, tapering to a point, reflexed at anthesis, thin, almost chaffy; stamens 6, borne at the mouth of corolla tube, filaments elongate, gradually tapering from a fleshy base, anthers elongate, medifixed, versatile, latrorse, connective narrow; gynoecium top-shaped, carpels 3, distinct basally, united through the long slender styles, ovule basal, erect, (?)anatropous. Pollen ellipsoidal, with slight to extreme asymmetry; aperture a distal sulcus; ectexine tectate, rugulate or reticulate, aperture margin slightly finer; infratectum columellate; longest axis 35–51 µm; post-meiotic tetrads tetrahedral, tetragonal or decussate, proportions not recorded [2/2]. Fruit small, broadly ellipsoidal to globose, often falling with the pedicel and unilaterally ruptured calyx tube attached, blackish, stigmatic and abortive carpel remains apical; epicarp smooth, thin, mesocarp thin, fleshy with a few flattened longitudinal fibres, endocarp thin, crustaceous, not adherent to the seed, smooth within. Seed ellipsoidal, somewhat compressed, hilum eccentrically basal, raphe extending 2/3 the length of the shining red-brown seed coat, loosely branched laterally, seed coat intrusion very thin, endosperm homogeneous; embryo basal. Germination remote-ligular; eophyll entire, lanceolate. Cytology: 2n = 36.
    Morphology
    Leaf (Tomlinson 1961), roots (Seubert 1997), floral (Morrow 1965).
    Distribution
    Two closely related species: Washingtonia filifera occurs in southeastern California, western Arizona, and Baja California; W. robusta in Baja California and Sonora, Mexico.
    Diagnostic
    Striking solitary hermaphroditic tree fan palms native to desert oases in southwestern USA and northwestern Mexico, distinctive in the long inflorescences with bracts that split and open out, becoming almost sword-like, and the chaffy petals and sepals.

    Images

    Distribution

    Native to:

    Arizona, California, Mexico Northwest

    Introduced into:

    Algeria, Bolivia, Canary Is., Cyprus, East Aegean Is., Florida, Hawaii, Italy, Kriti, Madeira, Mexico Northeast, Nevada, New South Wales, New Zealand North, Réunion, Sicilia, Spain

    Washingtonia H.Wendl. appears in other Kew resources:

    First published in Bot. Zeitung (Berlin) 37: 68 (1879)

    Accepted by

    • Govaerts, R. & Dransfield, J. (2005). World Checklist of Palms: 1-223. The Board of Trustees of the Royal Botanic Gardens, Kew.

    Literature

    Palmweb - Palms of the World Online
    • J. Dransfield & N. Uhl & C. Asmussen & W.J. Baker & M. Harley & C. Lewis, Genera Palmarum. The evolution and classification of palms. 2008

    Sources

    Kew Backbone Distributions
    The International Plant Names Index and World Checklist of Selected Plant Families 2018. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    © Copyright 2017 World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

    Kew Names and Taxonomic Backbone
    The International Plant Names Index and World Checklist of Selected Plant Families 2018. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    © Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

    Palmweb - Palms of the World Online
    Palmweb 2011. Palmweb: Palms of the World Online. Published on the internet http://www.palmweb.org. Accessed on 21/04/2013
    Content licensed under Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License http://creativecommons.org/licenses/by-nc-sa/3.0