Washingtonia H.Wendl.

Scientific Description

Family Arecaceae.

Habit and leaf form. Robust, tall ‘arborescent’ (treepalms); evergreen. Plants spiny. Pachycaul. Mesophytic, or xerophytic. Leaves small to very large; alternate; spiral; leathery; petiolate (margins strongly armed with curved teeth); sheathing. Leaf sheaths tubular (with a conspicuous abaxial cleft below the petiole); with joined margins. Leaves compound; epulvinate; palmate (costapalmate, blade divided irregularly to c. 1/3 its length into linear single-fold segments, bifid at their apices). Leaf blades without cross-venules. Leaves ligulate, or eligulate; without a persistent basal meristem (presumably). Vernation conduplicate. Leaves becoming compound by ontogenetically predetermined splitting. Vegetative anatomy. Plants with silica bodies. Leaf anatomy. Leaf blade epidermis without differentiation into ‘long’ and ‘short’ cells. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present, or absent. Anemophilous, or entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in panicles. The terminal inflorescence unit cymose. Inflorescences axillary, or terminal; flowers spirally arranged on short, slender rachillae; spatheate. Flowers small; more or less regular; 3 merous; cyclic. Perigone tube absent. Perianth with distinct calyx and corolla, or of ‘tepals’; 6; 2 -whorled (3+3); isomerous; sepaloid and petaloid; different in the two whorls; white, or cream. Calyx if outer whorl so interpreted, 3; gamosepalous; lobed. Calyx lobes irregularly tattered. Calyx imbricate; chaffy; persistent. Corolla if inner whorl so interpreted, 3 (exceeding the calyx); gamopetalous; valvate; thin, almost chaffy. Androecium 6. Androecial members adnate (to mouth of corolla tube); free of one another. Androecium exclusively of fertile stamens. Stamens 6; diplostemonous. Anthers elongate; medifixed; versatile; dehiscing via longitudinal slits; latrorse; tetrasporangiate. Gynoecium 3 carpelled. Carpels isomerous with the perianth. Gynoecium syncarpous; synstylous. Stigmas dry type; papillate; Group II type. Ovules non-arillate; anatropous.

Fruit and seed features. Fruit fleshy; not an aggregate, or an aggregate (when more than one carpel develops). The fruiting carpel indehiscent; often falling with the pedicel and ruptured calyx tube attached. Fruit 1 seeded. Seeds ellipsoidal, somewhat compressed; endospermic. Endosperm ruminate, or not ruminate; oily, or not oily. Seeds without starch. Cotyledons 1. Embryo achlorophyllous. Seedling. Germination consistently cryptocotylar (regardless of cotyledon form). Hypocotyl internode absent. Seedling collar not conspicuous. Cotyledon hyperphyll elongated, or compact; non-assimilatory. Coleoptile present, or absent. Seedling cataphylls absent. First leaf dorsiventral. Primary root persistent, or ephemeral.

Physiology, biochemistry. Photosynthetic pathway: C₃.

Geography, cytology, number of species. N = 18.

Additional characters Pollen grains mono- sulcate.