Invasive Species Spotlight: Caesar Weed
It's no secret how this plant spreads- just look at your boots, sleeves, and hair after a hike through the woods!
If you hike, hunt, boat, fish, or bird-watch in Florida, you've probably spent some time removing Caesar weed seeds from your clothes, boots, hair, or (hopefully not) your pets’ fur. These seeds will make you contemplate throwing away your hiking boots or possibly shaving your head. If you leave even one seed stuck to a piece of clothing and throw it in the wash, it'll inevitably end up in the sock you put on the next day. Annoying, scratchy, and as sticky as Velcro, these seeds spread to new areas by hitching a ride on humans and animals. Given how easily it disperses, it's no wonder that this is one of the most aggressively invasive plants in Florida.
Caesar weed is a pan-tropical species, found in almost every country near the equator. Its spread began hundreds of years ago- in fact, it's been spreading for so long that nobody is quite sure where its native range is. Scientists disagree on whether the plant is native to Asia or Africa, and many countries where Caesar weed was probably introduced now list it as a native plant. Caesar weed was probably spread intentionally to be used as medicine and as a fiber crop like jute or cotton. It was brought to Florida sometime before 1900, and by the early 20th century had already become a nuisance plant, invading natural areas and forming dense thickets.
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| Caesar weed seeds |
Tall, slender, and fast-growing, Caesar weed can reach a height of ten feet. In most areas, it's an annual, but in some warmer spots (or during unusually warm years) it acts as a perennial. Caesar weed is often seen growing in open areas that have been disturbed in some way like pastures, utility right-of-ways, and roadsides, but it's not picky- it'll grow almost anywhere and can even tolerate salt spray on the coast. It spreads extremely aggressively and can crowd out native ground cover plants and grasses. In some areas, Caesar weed is capable of creating dense monocultures, or areas where it's the only plant species. Each plant produces dozens of small, spiky, brown seeds, which cling to almost any surface. In the wild, these seeds are spread by deer, squirrels, hogs, and many other animals, and they can remain viable in the soil for years.
Unfortunately, hikers, bikers, hunters, and other outdoorsy folks have become another important vector for the spread of Caesar weed. It’s tedious, but removing the seeds from clothing, boots, and hair before leaving a hiking spot is the best way to slow the spread of this invader. The best way to ensure that those seeds don’t sprout is to put them in a sealed plastic bag and throw them away; if you don’t have a bag handy, at least leave them in the same spot and don’t spread them to a new park or preserve (or, heaven forbid, your own backyard).
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| Caesar weed leaf |
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| very young Caesar weed seedlings |
If you have Caesar weed on your property and want to remove it, hand pulling is the best way. Make sure you remove all of the seeds and bag the plants tightly. A thick layer of mulch will stop existing seeds from germinating and undoing all of your hard work!
Links to follow for more information:
- the University of Florida Institute of Food and Agricultural Science's web page on caesar weed
- the UF IFAS overview page for Florida's invasive plants
