How are noxious weeds classified?

Noxious weeds are classified primarily by legal designation that indicates their harmful impacts on agriculture, horticulture, ecosystems, and human health. This classification is established by state and federal laws, which categorize certain plants as noxious based on their ability to outcompete desirable plants, harm crops, and negatively affect the environment. Such legal designations help in the control and management of these invasive species, ensuring that resources are allocated for eradication and preventing their spread.

The other options do not accurately reflect how noxious weeds are identified. For example, while growth speed and height might contribute to the characteristics of a plant, they do not determine its classification as noxious. Also, beauty is subjective and does not play a role in identifying plants that can pose risks to ecosystems and human interests. Hence, legal designation is key in defining noxious weeds.