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Pistia spp.
water lettuce
Overview
Pistia spp. is a genus in the arum family Araceae containing the single free-floating aquatic species Pistia stratiotes, known as water lettuce, now found throughout the warm fresh waters of the world. Plants float on the surface as rosettes 4-12 inches (10-30 cm) across of spongy, wedge-shaped, pale blue-green leaves covered in short water-repellent hairs and marked by deep parallel ribs. A dense tuft of feathery roots hangs beneath, drawing nutrients straight from the water. New rosettes form on short runners, so plants quickly build into floating mats. The flowers are tiny and easily overlooked, held in a small pale green spathe less than 0.5 inch (1.3 cm) long near the center of the rosette. Pistia spp. grows in still and slow-moving fresh water such as ponds, lakes, ditches, and backwaters in frost-free climates. It is killed by frost and by drying out, and its rapid spread forms dense surface mats that shade out other aquatic life, so it is listed as an invasive weed in many regions and its cultivation and movement are restricted by law in several places.
Native Range
Pistia stratiotes grows throughout tropical and subtropical fresh waters worldwide, and its exact native origin is uncertain, with Africa and South America both proposed. It occurs in ponds, lakes, slow rivers, canals, and swamps.Suggested Uses
Used in frost-free ornamental ponds and container water gardens for surface cover and shade, and in aquaria as a floating plant. In many regions its use is limited or prohibited because of its invasive spread.How to Identify
Appearance
Size & Dimensions
Height2" - 6"
Width/Spread4" - 1'
Bloom Information
Flowering is inconspicuous and easily missed, with tiny flowers enclosed in a small pale spathe at the center of the rosette, mainly in warm weather. Reproduction is mostly vegetative, by daughter rosettes on short runners. Berries with small seeds form only occasionally.
Detailed Descriptions
Foliage Description
Pale blue-greenGrowing Conditions
Sun Requirements
Requires 5-10 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Grow Pistia spp. as a floating plant on the surface of still or slow fresh water in full sun to part shade, in frost-free conditions or as a summer-only plant lifted before cold. It draws all its nutrients from the water and needs no soil, multiplying rapidly when water is warm and moderately fertile. Warm water above about 60F (15C) drives growth, while frost and freezing kill the rosettes outright. Crowded mats are thinned regularly by scooping out surplus rosettes, keeping the water surface partly open. In cold climates a few rosettes are overwintered indoors in a warm, bright tank. Because of its weedy spread, plants and trimmings are disposed of well away from natural waterways.Pruning
Thin the floating mat regularly by removing excess rosettes by hand or net through the growing season. Lift and discard yellowing or crowded plants to keep the colony healthy. No cutting is needed beyond removing surplus growth.Container Growing
Suitable for container growing
Minimum container size: 2 gallons