Most likely it is "Poa annua", annual bluegrass, This is a cold weather "weedy" grass that will die out in a few weeks. It is often used as a nurse grass in seed mixes since it does germinate much more quickly than most others. Most often, in established lawns, the seed will germinate and start to grow in late August and most all pre emergent need to be in place about 6 weeks before, so usually mid July is when to put them down.

Thank you both. We did get our money's worth as far as I'm concerned; our entire yard was hopelessly overgrown and it took 4 men 9 hours to get it cleared out. This is just one plant in one small bed, and I didn't specifically ask them to remove these plants. That was my mistake. My guess is that they assumed they were lilies that I wanted to keep. They did a perfect job with everything else so I'm not at all dissatisfied with them. Knowing what they are and what to do really helps me; I can go out and dig up some of the roots and thin them out, and then see what happens next spring. They have been in for 10 years and never flowered, but perhaps they've always been too crowded. I'll give it a try and see if I get any blooms next year. Thanks for your help!

Poast and Select are two herbicides meant for grass, both are expensive. They work best on young grasses, 5 to 6 leaf stage. Older grasses, react more slowly (2 to 3 weeks). Once they begin to head out, forget it. You could try wiping them with a mild solution (1%) of Round-up. Put on a latex glove with a cotton glove over top. Dip your hand in the solution and grab the leaves you can get at without dripping or touching your ornamentals then pull up. Try not to damage the leaves but get as much Round-up on the pest as you can. Again though, if the grass is mature, the results will be less than desirable.

I have used Roundup around the base of many trees and it has never harmed the trees. I would never (again) use a weed barrier like plastic. I believe the rule-of-thumb for mulching around trees is no more than 6" deep around the tree.