Erysimum scoparium (Canary Island wallflower)

CC image from Pixabay

 This plant is endemic to the high altitude areas of Tenerife and La Palma.

It grows in bushy cushion-like clumps, and has long, narrow, slightly blueish leaves (if squeezed these may have a cabbagey smell - this plant belongs to the Brassicaceae or cabbage family).

The four-petalled flowers change colour from white to purple as they age. It's thought the white ones contain more nectar, while the purple ones are more visible to insects from further away. Although there aren't many in January, you will see a few of these flowers.

I read that the underside of the leaves have T-shaped hair-like outgrowths (called trichomes) - however, I couldn't see these on our trip this year when I looked. "If they exist" they may be an adaptation to deter herbivorous insects. The leaves were furry - perhaps the trichomes were just really tiny. Such structures may affect transpiration rate and leaf temperature by influencing the boundary layer of the leaf surface.