株
zhū · HSK 7
plant
🌱 株 = 木 wood + 朱 zhū (red); 朱 lends the sound, 木 marks a tree stub or single plant
The 木 wood radical ties it to plants, while 朱 (zhū, red) is purely phonetic and gives the reading zhū. Core senses run from a tree stub to one individual plant, and it also counts plants like a measure word.
株 — tree 木 + vermilion 朱 (phonetic)
A semantic-phonetic compound: 木 ('tree') gives the meaning while 朱 supplies the sound 'zhū'. It originally referred to the exposed stump or trunk of a tree at ground level, and from that root sense it came to serve as a measure word for individual plants and, in modern usage, for shares of stock.