菩

A phono-semantic compound:

艸 (“grass, plant”) — semantic element, chosen as in many Buddhist transliteration characters.

咅 (bu/pú, phonetic) — phonetic element, providing the sound.

This character was coined in Buddhist transliterations from Sanskrit.

In 菩薩, 菩 transcribes the first syllable of bodhi (enlightenment, awakening).

菩薩 (보살) — bodhisattva (“enlightenment-being”)

菩 is almost never used outside the compound 菩薩.

Together, 菩薩 transliterates bodhisattva (Sanskrit: बोधिसत्त्व), literally “one who seeks enlightenment for all beings.”

The 艸 radical is ornamental here, not semantically related to “plants.”