榆

Left tree radical (Kangxi #75) — pictograph of a tree with trunk, branches, and roots. Indexes 榆 as a species name. Same radical anchors most tree species: 松 (pine), 柏 (cypress), 杨 (poplar), 柳 (willow), 桃 (peach). The radical states 'this is a tree' before you process the phonetic on the right.

Right 俞 supplies the sound — yú unchanged. 俞 originally pictured a hollowed-out canoe; the meaning doesn't carry into 榆. Pure phonetic. Same phonetic in 愉 (pleased), 输 (transport), 喻 (analogy), 偷 (steal). The elm is a venerable Chinese tree; the literary 桑榆 'mulberry-and-elm' connotes old age, since both grow where the sun sets.