What is "umbrella grass"

Several species of plants are known by the common name umbrella grass or umbrella-grass, including:

• Chloris truncata, a grass
• Cyperus alternifolius, a sedge
• Digitaria divaricatissima, a grass
• Many species of the grass genus Enteropogon, such as Enteropogon acicularis
• Several species of the sedge genus Fuirena