Tis the season of white trees, purple groundcover and phlox-like patches along the road.
Hawthorn trees (Crataegus species) and catmint (Nepeta species) are common highway plantings because they're attractive and tolerant of roadside conditions -- pollution, heat and drought.
The hawthorns' dense crowns help with noise suppression.
There's an Old World saying, "It's bad luck to approach a hawthorn tree at night." To that, we pose a New World saying, "Duh, you think?!" (Below, cockspur hawthorn leaf and thorn, C. crus-galli)
Catmints' ground-smothering habit helps control roadside weeds. If your window's open and traffic's slow you might catch the hawthorn flowers' scent, which can be somewhat fetid. Perhaps the catmint's more pleasant smell will make up for it.
Sweet rocket (Hesperis matronalis, also known as dame's rocket) is an Old World import that escaped to the New World wilds. It's biennial and its seed readily colonizes almost any kind of disturbed ground. Sweet refers to its fragrance, most notable late in the day, and dame to its historic medicinal uses for "female troubles."
Some people call it wild phlox based on its stature and flower form, although sweet rocket is a 4-petal mustard family member, not related to the 5-petal tall phlox gang.
Catmint Nepeta species