Red Clover (T. pratense) is more common and very similar, and grows in most of the same places. The best way to tell the difference is by the leaves, which in Red Clover usually (but not always) show a chevron pattern but are unmarked in Alsike Clover; and by the color of the flowers, which in Alsike Clover is less magenta and more pale rosy pink, with young white flowers in the center of the head. In fact, it does look like something halfway between Red Clover and White Clover (T. repens), which may account for the specific name hybridus for a plant that is not a hybrid.

This plant grew in a meadow near Cranberry, where it was blooming in the middle of June.

Gray describes the genus and the species:

TRIFOLIUM [Tourn.] L. CLOVER. TREFOIL

Calyx persistent, 5-cleft, the teeth usually bristle-form. Corolla mostly withering or persistent; the claws of all the petals, or of all except the oblong or ovate standard, more or less united below with the stamen-tube; keel short and obtuse. Tenth stamen more or less separate. Pods small and membranous, often included in the calyx, 1-6-seeded, indehiscent, or opening by one of the sutures. Tufted or diffuse herbs. Leaves mostly palmately (sometimes pinnately) 3-foliolate; leaflets usually toothed. Stipules united with the petiole. Flowers in heads or spikes. (Name from tres, three, and folium, a leaf.)

T. HYBRIDUM L. (ALSIKE C.) Resembling T. repens, but the stems erect or ascending, not rooting at the nodes; leaflets ovate, rounded at apex; flowers rose-tinted. Generally common. (Introd. from Eu.)

Everlasting Pea is a vigorous vine that can take over whole hillsides. It compensates us for the space it takes with a glorious array of flowers in shades from white through deep magenta, often (as here) with stripes or bicolor patterns.

Gray describes the genus and the species:

Style dilated and flattish (not grooved) above, hairy along the inner side (next the free stamen). Sheath of the filaments scarcely oblique at the apex. Otherwise nearly as in Vicia. Our species perennial and mostly smooth plants. (Lathyros, a leguminous plant of Theophrastus.)

L. latifolius L. (EVERLASTING or PERENNIAL PEA.) Tall perennial with broadly winged stems; leaves and stipules coriaceous and veiny; petioles mostly winged; the 2 elliptic to lanceolate leaflets 0.5-1 dm. long; peduncles stiff, many-flowered; flowers showy, pink, purple, or white. Frequently cultivated, and escaping to roadsides and thickets, Ct. to 1). C. (Introd. from Eu.)

Another picture is here.

Sometimes called Perennial Sweet Pea. These weedy vines cover hillsides in residential neighborhoods, often where they had been planted generations before. Once you have Everlasting Peas, you have them forever. But is that such a bad thing?

From Gray’s Manual of Botany: L. latifolius L. (EVERLASTING or PERENNIAL PEA.) Tall perennial with broadly winged stems; leaves and stipules coriaceous and veiny; petioles mostly winged; the 2 elliptic to lanceolate leaflets 0.5-1 dm. long; peduncles stiff, many-flowered; flowers showy, pink, purple, or white. Frequently cultivated, and escaping to roadsides and thickets, Ct. to D. C. (Introd. from Eu.)

(This was from the 1908 edition. The 1890 edition does not list Lathyrus latifolius, suggesting that it had not yet become established as a frequent escape.)

Wherever there are hillsides that no one wants to mow, there is crown vetch. Its cheerful vigor means that it often escapes and invades a hillside on its own, but its happy clover-like pink flower heads make us willing to forgive its bad manners.

You see it everywhere, but do you ever stop to look at it close up? This is your chance. Take a moment to contemplate the beauty of white clover in an ordinary lawn.