Glauca is a word that crops up in the naming of several plants. Like many Latin derived names it is descriptive as with the Noble Fir Tree  above ‘Abies procera glauca’. The leaves are glaucous, which is from the Latin word glauca, meaning bluish-grey. (Procera mean tall in Latin)

Glauca also refers to the fact that some plants have a powdery white coating on their leaves or stems. This coating, sometimes called a bloom or farina creates the grey colouring that can lead to the Glauca name.
Glaucous-leaved trees and plants contrast gently with the shades of green around them and combine well with almost any other color making them useful in landscaping and garden design.

Glaucous Plants

Nicotiana glauca Tree Tobacco is a much branched shrub or small tree often reaching 25 feet
Picea glauca (White Spruce) is a species of spruce native to the north of North America
Festuca glauca Elijah Blue the Blue Hair Grass
Rosa Glauca rubrifolia the flowers are not remarkable, being small, single and pink but the plum-grey foliage is unique.
Yucca and Canna both have a glaucous form
Plums and grapes often have a grey white bloom on the ripe fruit.

Consider using these grey-green combinations in your garden with Rue or Rudbeckia maxima as further examples.