I think you'll find rose of sharon is commonly used for most Hypericums, including Hypericum 'Hidcote' - that's why common names are pretty useless really.

Indeed Bamboo - Our native Arum maculatum apparently has over 60 common names, so that, in former times, people from neighbouring counties wouldn't have a clue which plant each was referring to....

"Rose of Sharron" is barely any more useful, since, along with various Hypericums, the name has also been used for an Hibiscus and an Allium - so that's three completely unrelated plants, none of which have any connection with Roses, whilst the biblical "Rose of Sharron" is probably a Crocus or Tulip.