I have seen these very pretty "English Daisies" blooming every year in the exact same location for the past several at 8,000' elevation in south central Montana. My guess is that they are Bellis perennis, but they have a toothed edge on their leaves. While I did not plant these flowers, they may have resulted from some wildflower seeds used by the contractor when the house was being finished and landscaped. I see no other similar flowers anywhere on the property. The flower heads are about 3.5" in diameter, and the plants stand about 30" tall. I am certain these are not the Oxeye Daisy since there are several groups of Oxeye Daisy on the property, and they appear totally different. In the leaf picture, the smaller leaf is from an Oxeye Daisy, and the large one is from the daisy about which I am concerned.
Sorry, looks like oxeye daisy, Leucanthemum vulgare to me. Your first photo shows leaves the same as what you indicate as oxeye daisy. The basal leaves on oxeye daisy have a different shape than the stem leaves. I believe your third photo shows the leaf variation of L. vulgare.
The Oxeye Daisies seen here in the Big Sky, MT region look totally different than the photos previously submitted. There are many fewer leaves along the stems, the plants are only about half as high, and the flower and, indeed, the entire plant is much smaller. The attached photo is a group of Oxeye Daisies growing approximately 100 meters from the larger daisies. In the second photo you see stems of the subject plant (top) next to that of an Oxeye Daisy (bottom). The appear totally different.
I was headed in the same direction as Ron. To quote Allan Armitage's Herbaceous Perennial Plants (3rd ed.): Armitage also lists about 20 cultivars of the Shasta daisy.
