Washingtonia H.Wendl., Bot. Zeitung (Berlin) 37: 68 (1879)

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Arizonapresent (World Checklist of Arecaceae)B
Californiapresent (World Checklist of Arecaceae)B
Floridapresent (World Checklist of Arecaceae)B
Hawaiipresent (World Checklist of Arecaceae)B
Mexico Northwestpresent (World Checklist of Arecaceae)B
Nevadapresent (World Checklist of Arecaceae)B
New South Walespresent (World Checklist of Arecaceae)B
Réunionpresent (World Checklist of Arecaceae)B
Spainpresent (World Checklist of Arecaceae)B
Two closely related species: Washingtonia filifera occurs in southeastern California, western Arizona, and Baja California; W. robusta in Baja California and Sonora, Mexico. (J. Dransfield & N. Uhl & C. Asmussen & W.J. Baker & M. Harley & C. Lewis, Genera Palmarum. The evolution and classification of palms. 2008)A



Biology And Ecology

Common Name


  • 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. (J. Dransfield & N. Uhl & C. Asmussen & W.J. Baker & M. Harley & C. Lewis, Genera Palmarum. The evolution and classification of palms. 2008)A