Both are accepted names in the Plant list. I think where the var. name is the same as the species name they are usually the same, it might be that where there are several variety names in use then both can be used to distiguish one variety from another, if variety is not know it can be assigned to the straight species. Where there are no other varieties it might be considered unnecessary to use a variety name.
http://www.theplantlist.org/tp...
Accepted Name
This is the name which should be used to refer to the species (or to a subspecies, variety or forma).
For each name with Status of ‘Accepted’ The Plant List aims to provide:
•the name currently accepted as the one which should be used in preference to refer to this species (or subspecies, variety or forma);
•the author(s) credited with publishing that name;
•the place and date of original publication of the name where this was supplied;
•a reference to the source database supplying this name record that recorded the opinion that it is an accepted name (with, where possible, a link to that record in the source database);
• other names (synonyms) considered to refer to that species;
• the IPNI↗ identifier (linking the name record to the International Plant Names Index, a bibliographic resource which will provide full original publication details for this name);
• an assessment of the Confidence that The Plant List attaches to the name being accepted. (This is an indication of the confidence that the Status of the name is correct).
