ROSA, in botany, a genus of the icosaandria polygamia class. The petals are five; the calix has five fleshy segments; and the seeds are numerous, rough, and inserted into the interior side of the calix. There are 14 species, five of them natives of Britain, viz. the eglanteria, or sweet briar; the spinosissima, or burnet rose; the arvensis, or white-flowered dogs-rose; the villosa, or apple-rose; and the canina, or red-flowered dogs-rose, or hip-tree.