I may be wrong but as I understand it there is no difference.

Wallflower (cherianthus) are short lived perennials that are generally treated as biennials.

The reason being is that after a couple of years they become a bit ' woody' and often sparse of flowers so because of the easiness to grow from seed, many people just renew them each year.

This is what I do!

I stand to be corrected with this point of view...Tg

A comment a few days ago suggested than you can cut them back after flowering, so I'm going to try that this year, & apparently you can also take cuttings which is worth a try.

there so cheap to buy i wouldnt bother

Very true, but then they say that a penny saved is a penny earned...