Powdery Thalia (Water Canna)

Powdery thalia flower cluster
Species of Conservation Concern
Scientific Name
Thalia dealbata
Marantaceae (arrowroots)

With its large, paddle-shaped, blue-green leaves, powdery thalia looks a lot like the tropical cannas so common in landscape plantings. In late summer, this native pond or marsh plant produces tall spikes of purple flower clusters.

Thalia is an herbaceous perennial growing from thick rhizomes. The leaves give this plant a tropical look. The thick stalks are longer than the paddle-shaped or lanceolate blades. Combined, the leaf stalks and blade may reach 10 feet in height, making them the largest leaves of almost any native North American plant, excluding the leaves of palm trees.

The entire plant appears to be dusted with a fine white powder (glaucous-coated), hence the name powdery thalia.

The flower stalk is a tall wand bearing clusters of purple blossoms. The flowers are in tight, side-by-side pairs along the zigzag flower-stalk branches. The actual petals are not very showy. What appear as petals — the showy purple structures — are actually highly modified stamens. Blooms July–August.

Similar species: Pickerel weed (Pontederia cordata) is probably most likely to be confused with thalia, but it is smaller (only to about 4 feet tall), has heart-shaped or lance-shaped leaves, with veins that all run parallel as opposed to running perpendicularly out from the midrib. Also, pickerel weed’s flower clusters are much denser; not as loose or open as they are in thalia.

Cannas (Canna species) are well-known, hardy, nonnative ornamentals common in landscape plantings. The foliage can be similar to thalia’s, but the flowers of canna are quite different: they are large and occur in showy clusters, and they have only warm colors: red, orange, yellow, pink, or combinations of those hues. Also, canna rhizomes tend to rot in soils that are wet or poorly drained, so they are unlikely to survive in the pond-edge or marshy habitats where thalia thrives.

Other Common Names
Hardy Canna
Powdery Alligator-Flag

Height: to 6 feet, sometimes to 10 feet. One of the largest herbaceous species in Missouri.

Where To Find

Grows naturally in the Missouri’s Bootheel lowlands north to Cape Girardeau County. Cultivated as an emergent pond plant statewide.

Thalia is an uncommon plant in Missouri, growing in shallow water in the swamps, drainage canals, and lake borders of the Bootheel lowlands.

The overall range of this species extends south and east from the Missouri Bootheel, extending from Florida to Texas and north to South Carolina and Oklahoma.

Due to its limited distribution and rarity in our state, powdery thalia is listed as a species of conservation concern in Missouri.

Thalia is an attractive and showy native ornamental plant for Missouri pond edges, large water gardens, bog plantings, or rain gardens. The effect is especially bold when they are massed together in a group. Note that if you want to cultivate thalia north of the Bootheel, you must protect its rhizomes from freezing. Some gardeners grow the plants in pots that are submerged in the pond in summer, then bring them indoors in winter. If you want to try overwintering them outdoors, they should generally be submerged in 18–24 inches of water and heavily mulched. Some people simply treat them as annuals and replant them each spring. They need full sunlight.

Because powdery thalia is listed as a Missouri species of conservation concern, it is irresponsible to remove this species from the wild. If you are interested in planting powdery canna, please obtain your starts from responsible plant nurseries.

Linneaus, the father of taxonomy, named the genus after Johann Thal (Johannes Thalius), a German physician and botanist who lived 1542–1583. Since, in German, his name is pronounced with a hard T sound (as in Thomas), the species name should probably be pronounced TALL-ya, instead of THALL-ya or THAY-lia. Johann Thal is known as the “father of floristry”; in his short life, he pioneered the process of creating regional floras — manuals of all the plants within a given area. The three-volume reference work The Flora of Missouri is a modern descendant of his idea.

The species name, dealbata, means “whitened” or “powdery”; it refers to the plant’s powdery whitish coating.

In his famous set of watercolors of North American birds, naturalist John James Audubon used powdery thalia in plate 183, his depiction of a male and female golden-crowned kinglet.

The family that thalia belongs to has more than 500 species worldwide, but most of these are in tropical and warm-temperate regions. The common houseplant called “prayer plant,” as well as the arrowroot plant that’s used for its edible starch are members of this family. Thalia is the only arrowroot family plant native to Missouri.

Missouri represents the northern limit of this plant’s native range. Like so many other species native to Missouri’s Bootheel, its numbers must certainly have declined due to habitat loss when the swamps of that region were drained for agriculture in the early 20th century.

The flowers of thalia and others in its genus are quite complex in form. The showy portions are actually highly modified stamens (pollen-producing structures), while the true petals are reduced in size and scarcely worth mentioning. As you might expect, there is an interesting pollination biology that goes along with the unusual flower form. The floral structures include a landing platform for insects and special appendages that function like triggers for other structures that push pollen onto and scrape pollen off of the appropriate pollinator insects — which apparently are carpenter bees and probably bumblebees. You can watch the spring-loaded tripping mechanism by inserting a pencil or thin stick into the throat of one of these flowers — if it hasn’t already been tripped by a bee!

Several species of ducks eat the seeds.

The Brazilian skipper, a butterfly that cannot overwinter in Missouri but expands its range north into Missouri each summer, uses thalia (and the related cannas) as a larval host plant. Its caterpillars live in nests they make by rolling up part of the leaves. They hide in safety during the day, then come out to chew the leaves at night.

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About Wildflowers, Grasses and Other Nonwoody Plants in Missouri
A very simple way of thinking about the green world is to divide the vascular plants into two groups: woody and nonwoody (or herbaceous). But this is an artificial division; many plant families include some species that are woody and some that are not. The diversity of nonwoody vascular plants is staggering! Think of all the ferns, grasses, sedges, lilies, peas, sunflowers, nightshades, milkweeds, mustards, mints, and mallows — weeds and wildflowers — and many more!