Water hyacinth (Pontederia crassipes)

Synonyms: Eichhornia crassipes, Eichhornia speciosa, Piaropus crassipes

Common Names: Common water hyacinth, floating water hyacinth

Description:

Water hyacinth (Pontederia crassipes, long known as Eichhornia crassipes) is a free-floating water plant from the Amazon basin of South America, brought to the United States in 1884 as an ornamental for water gardens [1]. It now grows across much of the country and is considered one of the world's worst aquatic weeds, forming dense floating mats with showy purple flowers [1][2]. MISIN tracks it because those mats block light and oxygen, crowd out native plants, clog waterways, and breed mosquitoes [1][2].

Habit:

Water hyacinth floats freely on the surface as a rosette of thick, glossy, rounded leaves [1]. Its giveaway feature is the leaf stalk: it is swollen and spongy, filled with air, and works like a built-in float that holds the plant up ? though in crowded mats the stalks stretch longer and less bulbous [1]. A mass of dark purple to black feathery roots hangs below the rosette [1]. When in bloom it sends up a spike of 8 to 15 showy lavender-blue flowers, each with six petals, and the upper petal has a yellow blotch [1].

The easiest time to spot it is summer into fall, when mats are largest and the purple flower spikes are out [1]. In northern areas the floating plants are usually killed by hard winter freezes, but the species can return from the pond and aquarium trade or from seed [1].

At-a-glance cues:

1. Free-floating rosette of thick, glossy, rounded green leaves [1]
2. Swollen, spongy, air-filled leaf stalks that act as floats [1]
3. Showy lavender-blue flower spike; the top petal has a yellow blotch [1]
4. Dark purple to black feathery roots hanging beneath the rosette [1]

Leaves:

1. Borne in a free-floating rosette [1]
2. Thick, glossy, and leathery; rounded to kidney-shaped, about 4?8 inches (10?15 cm) wide [1]
3. Smooth margins; held above the water on inflated stalks [1]
4. Bright green [1]

Stems:

1. No upright woody stem ? the plant is a floating rosette [1]
2. Leaf stalks (petioles) are swollen, spongy, and air-filled, up to about 12 inches (30 cm) long, acting as floats; they stretch longer and thinner in crowded mats [1]
3. Spreads on runners (stolons) that bud off new daughter rosettes [1]
4. A dense mass of dark purple to black feathery roots hangs below [1]

Flowers:

1. Showy and lavender-blue, with six petals [1]
2. The upper petal bears a yellow blotch ringed with darker blue [1]
3. Borne in a spike of about 8?15 flowers held above the water [1]
4. Bloom in the warm months; each flower has both male and female parts [1]

Fruit and seeds:

1. Fruit is a three-celled seed pod (capsule) holding many tiny seeds [1]
2. Seeds can stay dormant in the sediment and sprout after drying events [1]
3. Spread is mostly vegetative ? by daughter rosettes and broken fragments ? with seeds playing a smaller role [1]
4. The plant grows extremely fast and can double its cover in as little as two weeks [1]

Habitat:

Water hyacinth grows on still or slow-moving fresh water ? ponds, lakes, marshes, slow rivers, canals, and ornamental ponds [1]. It grows best in warm water (around 82?86 ?F / 28?30 ?C) and tolerates slightly salty water, but long winter freezes reduce or kill it, so floating plants in the North usually do not survive the winter [1].

The plant is native to South America (the Amazon basin of Brazil) [1]. It was introduced to the United States in 1884 and is now found in 40 or more states, mostly in the warm South and West, and it appears on the IUCN list of the world's 100 worst invasive species [1][2].

Reproduction:

Water hyacinth spreads mostly through people and moving water. It is sold for ponds and water gardens, and it escapes or is dumped into natural waters [1]. Once present, it multiplies astonishingly fast: each rosette sends out runners that bud off new plants, any broken piece can float away and grow, and a patch can double in as little as two weeks [1]. It also makes seeds that can lie dormant in the mud and sprout later, which helps it return after a die-off [1].

Because it grows and fragments so quickly, the keys to control are catching it early, removing every piece, never buying or releasing it, and cleaning gear before moving between waters [1].

Impact and Damage:

For people who use the water, water hyacinth forms thick floating mats that cover ponds and shorelines and make boating, fishing, and swimming difficult, and that clog water intakes, irrigation canals, and drainage so that water backs up and flooding gets worse [1][2]. The still water around the mats also breeds mosquitoes [1]. The plant is not poisonous to people or pets.

For natural areas, the dense mats block sunlight and can cut the oxygen in the water beneath them dramatically, which harms fish and other aquatic life, and they shade out and displace native water plants [1]. The mats also lose large amounts of water to the air, lowering water levels [1]. The damage is well documented and long-standing ? water hyacinth has blocked rivers and infrastructure in the United States since the late 1800s, and federal agencies have managed it for over a century [1].

Similar species:

Pickerelweed (Pontederia cordata) is a native relative with similar blue-violet flower spikes, but it is rooted in shallow water rather than free-floating, it has firm arrowhead-shaped leaves on slender stalks, and it lacks the swollen air-filled floats and does not form floating mats [1].

Anchored water hyacinth (Pontederia azurea) is a close relative with similar purple flowers, but it is rooted and trailing and its leaf stalks are not inflated into floats [4].

American frog's-bit (Limnobium spongia) is a small free-floating plant with glossy rounded leaves, but it lacks the bulbous bladder stalks and the showy purple flowers of water hyacinth [1].

Water lettuce (Pistia stratiotes) also floats and forms mats, but it has pale, velvety, ribbed lettuce-like leaves and no purple flowers or air bladders [1].

Monitoring and rapid response:

Signs to watch for:

1. Free-floating rosettes of glossy round leaves on swollen, spongy stalks, forming mats on still or slow water [1]
2. Showy lavender-blue flower spikes with a yellow blotch on the top petal, in the warm months [1]
3. Dark feathery roots hanging beneath the floating plants [1]

What you can do:

1. For small amounts in a pond, scoop or rake the floating plants out by hand ? they lift easily because they float free [1].
2. Remove every piece, including daughter plants and fragments, since each can grow into a new plant [1].
3. Bag and dispose of plants on land away from the water; never compost or dump them, and never release pond or aquarium plants into the wild [1].
4. Don't buy or keep water hyacinth for ponds or aquariums ? choose native floating plants instead.
5. Clean, drain, and dry boats and gear before moving between waters [1].
6. Check with your state aquatic agency before treating or clearing plants in shared or public water.
7. Because it regrows so fast from fragments, natural area crews and agencies use repeated mechanical harvesting that captures every piece, target small and new mats first, and monitor through the growing season [1][2].

When to call a professional:

1. Large mats covering a pond or waterway, or any infestation in large or flowing water.
2. Sites where hand removal cannot keep up with the fast regrowth.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Eichhornia crassipes (Pontederia crassipes) ? Species Profile. nas.er.usgs.gov
2. IUCN Global Invasive Species Database. Eichhornia crassipes (100 of the World's Worst Invasive Alien Species). iucngisd.org
3. USDA NRCS Plants Database. Pontederia crassipes (Mart.) Solms. plants.usda.gov
4. Wisconsin Department of Natural Resources. Water Hyacinth (Eichhornia crassipes) and Anchored Water Hyacinth (Pontederia azurea). dnr.wisconsin.gov

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