A voucher specimen is a pressed and thoroughly dried plant sample deposited in a herbarium, and is intended to be a permanent record supporting research purposes. A voucher may be a record of a plant's occurrence in a particular area, or a specific example of a plant used in a scientific investigation.
Proper vouchers display all the necessary attributes for complete identification of the plant, and are to be accompanied by accurate locality, habitat, collection time, and collector data.
Only plant populations vouchered by specimens deposited in Index Herbariorum http://sciweb.nybg.org/science2/IndexHerbariorum.asp recognized herbaria are represented on this map.