Zinnia n. : Any plant of the composite genus Zinnia, Mexican herbs with opposite leaves and large gay-colored blossoms. Zinnia elegans is the commonest species in cultivation.

Example:
How often do i water Zinnia flowers?

Taxonomy
Zinnia, unranked, free encyclopedia, Zinnia elegans, Mexican species, Zinnia maritima, 05-27, flower, Zinnia acerosa, foliage, family Asteraceae, Genus Zinnia, leaves, appearances, orange, plant, A. Gray, Kunth.

Defination from the web:
... Zinnia leaves are opposite and usually stalkless (sessile), with a shape ranging from linear to ovate, and pale to middle green in color. ...