In the Southern Song Dynasty, the painter Ma Yuan painted a beautiful picture of pine and bamboo, which was called "Three Friends in Cold Years". Winter is the season when all trees wither, but pines, bamboos and plums can still maintain their ecology in severe winter and remain unchanged year after year, so it means that friendship will last forever.
Plum, bamboo and stone are beautiful, bamboo is thin and longevity, and stone is ugly and elegant, meaning three beneficial friends.