What to plant for bees

As a general rule of thumb, say gardening experts, go for simple flowers, and avoid highly developed varieties.
 
This may account for the number of bees we have in the garden. They certainly love our
Sea Holly, hellebores, dandelions and celandines which all flourish.
 
More importantly bees are essential for the planet and in the worst-case scenario they could be extinct in thirty years.