In some areas you may need written permission to collect from the authorities. This is called a collecting permit. Some plants have small distribution ranges and others are widespread. GPS unit - a Global Positioning Unit uses signals from satellites orbiting the earth to give an accurate reading of the latitude and longitude at any point on the earth. This sort of plant is often small.
Some examples are grasses, poppies, petunias and peas.
Many vegetables are herbaceous plants. An herbarium may also have a plant research facility and library. In other words a plant growing where it should not be, and possibly causing trouble. A noxious weed is a weed that is considered by the authorities of an area to be a problem and needs eradication. This usually means 'finding out about' something.