Agrostis, which should always be written in italics with a capital "A" is the genus of over one hundred species of grasses.
These include the common golf turf species of:
A. stolinifera or
palustris - creeping bentgrass
A. canina - velvet bentgrass
A. tenuis - browntop
A. capillaris - colonial bentgrass
Within each turf species of bentgrass there are a multitude of varieties, especially with the creeping bent (Penncross, Pennlinks, A-1, A-4, Crenshaw, Providence, G-2, Cobra, etc.)
As pointed out above, ryegrasses are species of the genus Lolium. It should be written "ryegrass", without the hyphen.