What's the difference ?
The images are classified correctly ?
do not look for differences in flowers, there are obvious, take a look at these pictures only.
Good luck

There are phylogenetic indication that the Sideritis may belong in the genus Stachys. That has yet to be decided. There are many superficial similarities of Sideritis syriaca to Stachys byzantinia though when put side by side they are easily distinguished from one another. The Stachys byzantina however has many cultivars and some of those pictured here may be one of those. That being said, different climatological conditions create different growth habits and looks to a plant. Full summer and lots of sun will bring on the look seen in Marylin's photo. I believe they are all correct. Here are a couple of photos that will help show the differences. There is an entire plant of Sidertis syriaca here to the right. It's leaves are small, comparatively and all the same size on this one year old plant. You can see the veination as a darker green among the covering of the comparativley short fuzz. Tucked in at the left is a sprig of the smallest youngest growth from Stachys byzantinia and a few more mature sprigs to the left of that and one large leaf from the cultivar 'Big Ears'. All three of the Sideritis we grow here have a more shrub like structure and the leaves are about the same size throughout. Stachys byzantinia is more of a ground cover and has much larger leaves and the veination does not show beyond the midrib due to the much longer S. byzantinia also have leaves of various sizes as it ages to flowering.