What is the symbolic significance of elm in ancient poetry?

Elm is known as the "elm knot in one's heart", saying that it is difficult to understand and cut.

Elm-"elm" is a homonym of "elm" and symbolizes wealth. Citrus is a beautiful tree and a happy tree. Lilac tree symbolizes love and happiness, evergreen tree symbolizes friendship and evergreen life, and pine tree symbolizes eternity ~

Elm, also known as spring elm and white elm, etc. , known as "elm pimple", is a deciduous tree of Ulmaceae. The bark of young trees is smooth and grayish brown or light gray, while the bark of big trees is dark gray with irregular depth and rough longitudinal cracking. Branchlets glabrous or hairy, without swollen cork layer and raised cork wings; Winter buds are nearly spherical or ovoid. The leaves are oval, oval, etc. The leaf blade is smooth and hairless, the back of the leaf is pubescent when it is young, then it becomes hairless or some veins are tufted, and the petiole surface is pubescent. The leaves of flowers open first and gather in the axils of branches. Samara sparsely obovate and round. The flowering and fruiting period is from March to June (later in Northeast China).

Elms are distributed in northeast, north, northwest and southwest provinces of China, and also in Korea, the former Soviet Union and Mongolia. Born on slopes, valleys, rivers, hills and sand dunes below the altitude of1000-2500m.