January 30, 2019
Don't pull out the handcuffs so quick ... like many answers ... it depends on your situation. For example, according to the Texas Department of Public Safety picking the flowers in the public right of way is legal, but cautions against removing plants. Picking plants on private property will subject you to laws against criminal trespass, but you are perfectly protected by law to pick public wildflowers, even the state flower the Texas Bluebonnet.
[Video credit thanks to Chris Multop from The Multop Adventures]
On the other hand, there are areas designated by certain states as wildflower areas. These are often plainly marked and it is illegal to pick flowers in these areas. It’s considered a misdemeanor to pick wildflowers in California, New York, Virginia, Pennsylvania, West Virginia, Wisconsin, Oregon, and Colorado and you could be fined.
In National Forests, Parks or Monuments, it is illegal to pick or collect plants without a permit.  On Bureau of Land Management (BLM) land it is permissible to pick a few flowers, seeds, berries, seeds, nuts, cones or other plant parts in small amounts as long as they are not intended for commercial use. 
First, picking endangered or protected species is always illegal. Second, there are a number of traffic laws that create a problem for those picking wildflowers on the side of the road. For example, it is illegal to impede traffic, walk along or on a highway, block a road, street or highway or park on the median and usually on the emergency shoulder unless you are having an emergency. If you are on private land and you have been given permission by the owner than it is perfectly legal to pick the wildflowers.
Many wildflowers may wilt and perish soon after being picked, they are often fragile, meant to be enjoyed and admired not taken. Imagine an eye-popping, sherbert colored California Poppy, which provides an incredible buffet for native bees, but when picked lasts less than 24 hours in a vase. Wildflowers are there to support pollinators, birds, and small animals. We encourage you to grow wildflowers if you want to pick them. Butterflies, native bees, hummingbirds, and other insects, depend on seeds, nectar, and pollen for their food, and nutrients.
There is a beautiful sign in San Bruno park that says "Wildflowers are for everyone, please don't pick them." which is a motto I can stand behind. Because aesthetically, they are more potent when you let others enjoy their beauty as well, not to mention the benefit of pollen and nectar for the local pollinators. In states like Texas, Indiana, and Missouri, it’s technically legal but discouraged.
Unsure about your state’s laws? We recommend you contact your state’s Highway and Transportation Department to inquire further.
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