Mesembryanthemum \Me*sem`bry*an"the*mum\, n. [NL., fr. Gr. ? midday + ? flower.]

(Bot.) A genus of herbaceous or suffruticose plants, chiefly natives of South Africa. The leaves are opposite, thick, and f?eshy. The flowers usually open about midday, whence the name.

Source: Webster's Revised Unabridged Dictionary (1913)