Biology of Palms and Implications for Management in the Landscape

Abstract

Comprising a natural and distinctive group, palms (Arecaceae) differ from other woody plants in their structure and growth features that require or offer unique and sometimes advantageous landscape management opportunities. Although palms are a mostly tropical group that lacks dormancy and cold tolerance, there are numerous species possessing sufficient cool or cold hardiness to be suitable for landscaping in subtropical and even some temperate areas. The habit of palms is largely dependent on the number of stems and the length to which they elongate. There are solitary or multistemmed palms and tree or shrub palms. Regardless of habit, there is typically only one growing point or apical meristem per palm stem. Thus, multistemmed palms may be especially versatile landscape subjects because in many instances, one is able to control height and density by judicious removal of stems. The uniquely constructed palm stem, with growth restricted to its extremities (leaves and inflorescences distally, roots proximally, and wholly the product of primary growth), is composed largely of numerous, dispersed, hard, fibrous-sheathed, vascular bundles embedded in a matrix of water- and carbohydrate-storing parenchyma cells. Often likened to a steel-reinforced concrete column and offering tremendous strength and resiliency, palm stems lack a peripheral vascular cambium and, thus, capability for secondary growth, meaning they do not thicken much once they elongate vertically and there is no ability to repair damaged tissue. Thus, care should be taken when performing horticultural tasks to avoid making wounds (which are permanent, unsightly, and potential entry sites for pests and diseases) and damaging the sole apical meristem. A palm's total photosynthetic and reproductive efforts are concentrated into relatively few but large organs (leaves and inflorescences respectively), offering a unique opportunity to capture an entire year's worth of potential leaf, flower, and fruit litter before it falls into the landscape. The palm root system is adventitious and composed of numerous, small- to medium-sized, nonwoody roots. All primary roots are of a more or less constant diameter and arise independently from an area at or near the base of the stem called the root initiation zone. Because of these root system characteristics and the ability of their trunks to store water and carbohydrates, palms are relatively easy to transplant—even large specimens with small root balls—resulting in instant, mature landscapes.