Not according to the Catalogue of Life, the site we use as the "authoritative list of the world's species - maintained by hundreds of global taxonomists".
https://www.catalogueoflife.or...

Digging further, the COL uses KEW's POWO as their source for this genus. Here is the source page:
https://powo.science.kew.org/t...

And then https://powo.science.kew.org/t... states the source used to synonmise the two names:

Iwatsuki, K., Boufford, D.E. & Ohba, H. (2016). Flora of Japan IVb: 1-335. Kodansha Ltd., Tokyo.

If you can dig up a copy, that might tell you why they decided to combine the species.

Australis said: Digging further, the COL uses KEW's POWO as their source for this genus. Here is the source page:
states the source used to synonmise the two names:
Iwatsuki, K., Boufford, D.E. & Ohba, H. (2016). Flora of Japan IVb: 1-335. Kodansha Ltd., Tokyo.

If you can dig up a copy, that might tell you why they decided to combine the species.

That's interesting. I just looked at some work from the late W.George Schmid back in 2007 where he states the DNA content for H. rectifolia to be close but not equal to H. sieboldii and does not support that taxon's placement in synonymy with H.sieboldii. George only places H. rectifolia in synonymy with H. atroppurpurea; H. sachalinensis; H. apoiensis and the morph H. rectifolia f. albiflora (=H. 'Shirobana Tachi').