Taxonomie : D'après V.E. Rudd (Phytologia, 62(4): [282-]
291[-302]. 1987): "There is intergradation and it is often very difficult to distinguish these two varieties. Treating them as separate might not be justified and further study is desirable. The differences are slight and could be due to edaphic conditions rather than genetic. Some collections with smaller flowers actually are immature specimens."