For me, it's hard to define the peak moment for spring wildflowers in Kalamazoo. The season changes so quickly, as the woodland plants race for light. The flowers of early May tend to be bigger and showier than the early spring ephemerals. White Trillium (Trillium grandiflorum) seems to be the poster child for Spring.
Blue-eyed Mary (Collinsia verna) is an annual, while most of the other spring wildflowers are perennials.
I teach economics at Kalamazoo College. My wife is also an economist. We were on sabbatical in Europe for the 2014-15 academic year. (Salamanca, Spain, followed by Oxford, UK.) We were in Uruguay for the 2006-7 academic year.