Periwinkle or Myrtle, Vinca minor
Apocynaceae or Dogbane Family

Low, trailing vine, with shiny, dark-green, untoothed leaves that are opposite each other on the stems.  Near the ends of the vines, the leaves are so close as to appear whorled. Flowers with 5 blue, pinwheel petals, fused into a funnel at the base.  Blooming in spring.

Alien weed, spreading from cultivation, forming patches in scattered semi-shady locations in the park.

The blue pinwheel flowers and the trailing habit are distinctive.