Maryland designated the black-eyed susan as the official state floral emblem in 1918. The black-eyed susan is a daisy-like wildflower with yellow petals and a dark brown center that grows in dry places. A member of the sunflower family and native to the United States east of the Rocky Mountains, black-eyed susans are common in Maryland fields and roadsides.

Black-eyed susan plants reach 2 to 3 feet in height, blooming between May and August. The flower heads measure 2 to 3 inches in diameter. The scientific name is Rudbeckia hirta - "hirta" is Latin for "rough hairy" (as the prominent center of the flower is).

The root of the black-eyed susan is used in traditional and folk remedies to treat colds.

Source:

Maryland Symbols - State Flower: Maryland at a Glance

Links:

State Flowers - 50 States List
National Flower