Q: I have variegated monkey grass growing in my yard. Near it there is some non-varigated variety of grass coming up. Is this monkey grass?
A: You have two kissing cousins growing in the same spot. Variegated monkey grass is Liriope muscari ‘Variegata’. The shorter, dark green plant is mondo grass, Ophiopogon japonicus. The two look very similar but liriope is usually distinctly larger. In my observation, liriope flowers are more likely to be held above the leaves while mondo grass blooms are always inside the foliage.
Both are members of the lily family, not the grass family.
Truth be told, the two species are often misidentified. Some gardeners just call them both “lilyturf”. Scientists use the convenient term “liriopogon”.
I don’t think the two plant look good growing together…they do much better planted separately but both are excellent groundcovers in their own way.
I’d dig up the clump, separate the two and put them in separate semi-shady spots. There they will multiply and cover the ground nicely.