Mused about rock plant (5)
I believe the answer is:
sedum
'rock plant' is the definition.
'sedum' can be an answer for 'plant' (sedum is a kind of plant). I am not sure about the 'rock' bit.
'mused about' is the wordplay.
'about' is an anagram indicator.
'mused' with letters rearranged gives 'SEDUM'.
Can you help me to learn more?
(Other definitions for sedum that I've seen before include "Fleshy-leaved plant related to stonecrop" , "Mused about the rock plant" .)