Mistflower facts for kids

Quick facts for kids Mistflower
Scientific classification
Genus:	Ageratina
Species:	riparia

Mistflower (scientific name: Ageratina riparia) is a type of flowering plant that belongs to the daisy family, Asteraceae. It originally comes from Mexico. This plant has spread widely and can now be found in places like Cuba, Jamaica, and other parts of the Caribbean.

People also brought mistflower to new areas as an ornamental plant (meaning it was grown for its beauty). It has since grown wild in many places, including parts of Hawaii, South Africa, Southeast Asia, and Oceania. In warm, tropical climates, mistflower can become a serious invasive plant. This means it grows very fast and takes over areas, harming native plants. Because of this, many ways have been developed to control its spread.

What's in a Name?

The scientific name Ageratina riparia has an interesting meaning. The first part, Ageratina, comes from an ancient Greek word that means "un-aging." This refers to how the plant's flowers keep their bright color for a long time.

The second part, riparia, comes from the Latin word ripa, which means "riverbank" or "streambank." So, riparia means "growing on the banks." This tells us where you might often find this plant in nature.

Mistflower has many common names depending on where you are. In English, it's also called creeping croftonweed, river-eupatorium, spreading snakeroot, and William Taylor. In Hawaii, people call it hāmākua pāmakani. The word pāmakani means "windblown" in the Hawaiian language, which describes how its seeds are carried by the wind.

What Does It Look Like?

Mistflower plants with white flowers on La Palma, Canary Islands.

Mistflower is a low-growing plant that spreads out. It's a perennial, meaning it lives for more than two years. It can grow up to 1 meter (about 3 feet) tall in some places. The plant has strong roots, and its stems can be a bit woody and covered in purple hairs. If the stems touch the ground, they can even grow new roots!

The leaves of the mistflower are usually about 7.5 centimeters (3 inches) long and 2.5 centimeters (1 inch) wide. They are pointed at both ends and have jagged or serrated edges, except near the bottom. The leaves grow in pairs, opposite each other on the stem.

The flowers are white and grow in dense clusters at the ends of the branches. Mistflower usually starts to grow buds in July and August. It can flower from August all the way through March in some climates. Its seeds are small, black, and slender, with fine white hairs at the tip. These hairs help the seeds to be carried by the wind and water. A single mature plant can produce between 10,000 and 100,000 seeds each year!

Where Does It Grow and Why Is It a Problem?

Mistflower is originally from western Mexico. In its natural home, it doesn't grow everywhere and might even be rare. In the mid-1800s, people collected mistflower from Mexico and brought it to other countries to grow as a pretty garden plant.

However, outside of its native home, mistflower started to spread very quickly. It has now grown wild in many places, including parts of South Africa, tropical Asia, Oceania, Hawaii, and Peru. Mistflower has become a big problem in tropical and warm climates because it is an invasive plant.

In these areas, mistflower can form thick, dense patches of plants. Its branches can get tangled together, creating a "blanket" effect. This blanket blocks sunlight from reaching native plants below, stopping them from growing. For example, in Sri Lanka, it chokes out native plants in forests and pastures.

There's also evidence that when mistflower plants decay, they release chemicals into the soil. These chemicals can stop the seeds of native plants from sprouting, making it even harder for them to grow.

Mistflower can grow in both sun and shade, but it likes places with more light, like the edges of forests or along streambanks. It loves warm and humid places, especially subtropical and tropical forests. It can grow in most types of soil and can handle different humidity levels. It's also tough and can survive if animals try to eat it. However, mistflower can be harmful to horses if they eat it, so it's not good for grazing areas.

How Do We Control It?

A close-up of the underside of a mistflower leaf infected by a special fungus in Auckland.

Because mistflower spreads so much and causes problems, different countries have developed ways to control it since the mid-1900s. One way is to use mechanical methods, like trying to pull up the plants from the ground. People also use special chemicals called herbicides to kill the plant.

Using Nature to Fight Back

Another way to control mistflower is by using biological control agents. This means using natural enemies, like insects or fungi, to stop the plant from growing. Scientists look for things that only harm mistflower and don't hurt other plants.

Some successful biological control agents for mistflower include:

• A type of gall fly called Procecidochares alani.
• A plume moth called Hellinsia beneficus.
• A smut fungus called Entyloma ageratinae.

These natural enemies either damage the mistflower plants or stop them from spreading.

The smut fungus, Entyloma ageratinae, has been one of the most successful ways to control mistflower. This fungus is very specific to mistflower plants. In 1974, scientists found this fungus on mistflower plants in Jamaica, where the plant wasn't as invasive. After studying it to make sure it only harmed mistflower, the fungus was released in Hawaii in 1975. At one location, the area covered by mistflower dropped from about 75% to less than 1% in just nine months! This allowed native plants to grow back. The fungus spread quickly, especially in wet areas. After its success in Hawaii, the fungus was also brought to New Zealand in 1998, where it quickly infected many mistflower leaves.

Bumps (galls) on a mistflower stem caused by a special fly in Maui, Hawaii.

The plume moth, Hellinsia beneficus, from Mexico, was chosen because its young (larvae) eat the leaves of mistflower plants. After some attempts, the moth was successfully brought to Hawaii in 1973. This moth prefers higher places and has been good at controlling mistflower in those areas by damaging its leaves.

The gall fly, Procecidochares alani, spends its young stage inside the stem of mistflower plants. This causes a round bump, called a gall, to form at the top of the stem. This gall slows down the plant's growth and makes it harder for it to compete with other plants. This fly also only affects mistflower. It was first released in Hawaii in 1974. The moth and the fly together have helped control mistflower in high-altitude areas of Hawaii where the fungus might not be as effective. The gall fly was also introduced to Australia in 1987 and New Zealand in 2001. In New Zealand, the gall fly works well in dry areas, while the fungus prefers moist places. So, these two natural enemies work best when they are used together to control mistflower.

What Is It Used For?

Mistflower has mostly been used as an ornamental plant, meaning people grew it because it looks nice. It can also be used to help make leather (a process called tanning). In some places, it's used to help stabilize riverbanks or to mark land boundaries.

Near a village in India, people use the dried leaves and flowers of mistflower to make an herbal tea. They believe this tea can help lower blood pressure and blood sugar.

Scientists have also found that mistflower contains a special compound that can fight fungi. This means parts of the mistflower plant might be used to create a fungicide, which is a substance that kills harmful fungi. For example, it might help control a fungus that causes a disease in bananas.