In addition to identifying the 43 species, Schmid (1991) determined that 32 plants that were traditionally treated as species really did not qualify for that status. He recommended reclassifying these "species" as cultivars i.e. cultivated varieties.

The key reason was that there was no evidence that these plants ever existed as natural, "wild" populations. In fact, it appears that most of them were actually plants developed in nurseries by selection or through seedling propagation of crosses of unknown plants. This happened back in previous centuries in either their native Asian lands or after they had been brought to Europe and no records were kept on the plant's true history. 

Hostas previously thought to be species or botanical varieties but transferred to cultivar status by Schmid (1991) include:

Mr. PGC Link: HostaHelper information on Hosta Species...

Mr. Schmid continues his study of the genus, Hosta, and proposed another change affecting one of the all-time classic plants, Hosta sieboldiana. In his 2010 Species Update, W. George Schmid examined the origins of what was then the species, Hosta sieboldiana. The sports and hybrids of this plant account for more different cultivars in home gardens than any other hosta. In his extensive study, Schmid concluded that the plant grown in our gardens as H. sieboldiana is actually a hybrid cultivar developed in Europe after it was imported there from Japan by Philip von Siebold in 1862. One of the key factors in defining a species is that it may be found in the "wild" and that does not appear to apply to this hosta. Therefore, the proper name for this plant is H. ‘Sieboldiana’.

Kevin Walek, International Registrar for the Genus, Hosta made the following statement in his 2011 Registrations report:

"In a recent article W. George Schmid has proposed that the taxon H. sieboldiana be reduced to cultivar rank in accordance with the International Code of Nomenclature for Cultivated Plants (ICNCP). Refer to The American Hosta Society 2011 Online Hosta Journal, Vol. 42; under the section "Genus Hosta" by W.G. Schmid: H. sieboldiana or H. 'Sieboldiana': Species or Cultivar? or refer to the AHS 'Tan Book' (List of Species, Botanical Varieties, and Forms (under the International Code of Botanical Nomenclature (VIENNA CODE) and Species reduced to Cultivar Rank (under the ICNCP) posted on the AHS web site. The applicable plant description and synonyms are published in W.G. Schmid (1991) The Genus Hosta - Giboshi Zoku; Chapter 3, Part 2; Pages 93-94; 317-318. Timber Press; Portland, Oregon, USA.

Tthis change has been officially adopted by The American Hosta Society, but there seems to be ongoing disagreement concerning this change among some Hostaphiles. At the January 19, 2013 Hosta Scientific Meeting in Lisle, IL, Mark Zilis, author of The Hostapedia,  stated that Japanese hosta explorers think they have discovered a wild population of H. sieboldiana living on a remote part of one of the islands of Japan.

Bob Solberg of Green Hill Farm in North Carolina in The Hosta Journal (2018 Vol. 49 No 2) states that he and Mark Zilis of T&Z or Q&Z Nursery in Illinois on a recent trip to Japan found at least one example of the species form of H. 'Sieboldiana'  growing in the wild.

In the end, this change in nomenclature has been adopted by The American Hosta Society so we will use the form H. 'Sieboldiana' in our pages until or unless there is another change..