Herbaria records within the native range are often the best sources of information on the distribution of the target weed. Some herbaria will have records of all specimens in a computer database allowing easy access to information. In other herbaria, it may be necessary to look at each herbarium specimen of the target weed to get the information on its geographic distribution.
Botanists and amateur botanists can often add to the data obtained from herbaria and can advise on where the centre of origin may occur.
The information obtained from published papers through literature searches, herbaria, and personal communication with botanists should be compiled and mapped.
