(2) The rhubards, a taxonomic genus of plant belonging to the family Polygonaceae
Rheum is the serous or mucous discharge from the eyes or the nose during sleep. Rheum that accumulates and dries as a crust in the eyes has several names, e.g. sleepy sand, sleepy dust, and eye goop. Its components include mucin, skin cells, dust, etc. It forms during sleep because when awake the rheum is washed away through the tears from the nasolacrimal duct and with the blinking of the eye. There are certain conditions causing a considerable buildup of the rheum in the eye. Conjuctivitis and pink eyes are a common cause. The presence of pus in the rheum sometimes makes the opening of the affected eye difficult upon waking up.
In botany, Rheum is a taxonomic genus comprised of the rhubards. Members of this genus belong to the family Polygonaceae (knotweed family). There are about 60 perennial plants in this genus. Some of them are cultivated as food and for their medicinal value. The petioles of Rheum rhabarbarum, for instance, are used in making wine, pies, and jellies.