I have not seen these Emperors in the flesh, but I suspect the 'Emperor' part may be a trade name or trade mark; that is 'Emperor' signifies a company producing such plants, of already-known cultivars.

Things get a bit woolly here, depending on whether the trade name is registered or not, which may influence whether it should be included in the single quotes or not.

I won't go into detail, but consider the following - an excerpt from the FAQ at http://www.ipaustralia.gov.au/pbr/faq.shtml:

"Can the name of my variety be, or include as part of the name, a trade mark registered under the Trade Marks Act 1995?
No. A trade mark cannot be, or be part of, the variety name. However, it is possible to use a trade mark in conjunction with a variety name, with the variety name having equal prominence. For example, it might be decided to market a range of varieties under the trade mark Elle. So that one might have Elle ÂCelebrationÂ, Elle ÂAnniversary or Elle ÂApplauseÂ.
If a commercial name is registered as a trade mark it cannot be used as a variety name. If a plant is marketed under a trade mark without PBR protection, a purchaser may produce from the plant freely and sell the product provided they donÂt use the trade mark."