Thalia dealbata is a herbaceous, rhizomatous, marsh or marginal aquatic perennial, in the family Marantaceae. It is native to swamps, ponds and other wetlands in the Southern and Central United States and Mexico. Genus name honors 16th century German physician and naturalist Johann Thal.

Powdery Alligator Flag is that features long-stalked, canna like foliage and violet blue flowers. It grows up to 180-280 cm high. The near ovals to lanceolate leaves are blue-green in color, dusted with white powder on the surface and with purple edges. The flowers of Thalia dealbata occur in mid-summer in clusters at the tip of very tall, narrow stems. Violet flowers appear in branched open panicles atop scapes typically rising well above the foliage to 200-300 cm tall. If they do make it through to ripe, the pods split open to reveal the seeds.

Powdery Alligator Flag grow in wet soils or in shallow water in full sun. They are best in organically rich loams. It is happiest submerged in water and growing in full sun. During the day the plant holds its leaves more or less horizontally but in the evening the leaves all stand to attention in an upright position.

Propagation may be done by seeds or by division of rhizomatous stems. Grow as a marginal aquatic in a planting basket of fertile, loamy, humus-rich soil in up to 15 cm of water at the edge of a sunnty pool. In cold areas it will become deciduous. Plant may also be grown in we boggy areas. Plants are considered winter hardy to -20˚C.

Use in Landscapes: Thalia dealbata has been grown as an aquatic ornamental because of the pretty violet flowers and enormous leaves. It is a vigorous tropicalesque aquatic plant. It can be planted in the pond, swamp pot or the bog garden. Although it is very hardy, lends a tropical flavor to ponds and water gardens.