In early summer, these grass-like perennials produce multiple spikes of small, pale yellow blooms with dark yellow centers and faint purple stripes. The flowers rise above gray-green foliage. Native to open woods, meadows, and prairies of South America, these adaptable wildflowers tolerate a wide range of conditions and naturalize easily. The summer blossoms each open for just one day with the morning sun and close at dusk. Rarely do the blooms open on cloudy days. Plants grow to 3 feet tall and 10 inches wide.