An improved anchor device for retaining an erosion mat over a plant growingmedium layer in a green roof assembly. The anchor device includes a basememberhaving an elongate rod extending from a planar portion. The base member can beplacedin the green roof assembly with the rod projecting above the plant growinglayer and theerosion mat. A retainer is secured to the elongate rod and holds down theerosion mat.The retainer includes plant growth openings whereby plants rooted in the plantgrowinglayer may grow therethrough. A central opening in the retainer is defines byflexibleengagement members. The rod is received through the central opening and theengagement members engage annular indentations which are formed along the rodbetween annular protrusions. The engagement members extend at an acute anglerelativeto the rod.
