Whitman encourages us to "loaf" with him on grass that grows everywhere, and while he may witness "a spear" of that "summer grass," he also knows it comes in many shapes and sizes. As a result, the "grass" becomes a symbol of democracy. It can be any type of grass, but especially wild flowers such as blue flag and golden rod that grow in fields and streets everywhere in America. In "Leaf," one of Whitman's poems, he uses the image of the grasses waving at the wind to describe the freedom of all people living in America. He calls this picture of free citizens "the leaf." Then, later in the poem, he mentions other types of leaves besides just the grasses ones: the red maple leaf, the yellow mustard seed, and the white cottonwood tree leaf. So, yes, when Whitman writes about the "spear of summer grass," he is really referring to all types of grasses growing throughout America.