camphor tree
楠 centers on the camphor tree, a specific large evergreen tree known for its aromatic wood and camphor oil.
rhododendron
Rhododendron metternichii
Azuma rhododendron (Rhododendron metternichii var.)
Hakusan rhododendron (Rhododendron metternichii var.)
Tsukushi rhododendron (Rhododendron metternichii var.)
Kibana rhododendron (Rhododendron metternichii var.)
楠 combines 木 (tree) with 南, which likely contributes the sound. The character specifically names the camphor tree.
The left side is a tree 木, and the right side 南 (south) hints at a warm southern tree. Picture a large camphor tree growing in the south.
For ナン, imagine a camphor tree in the south (南, なん) with a nun resting under it: nun -> ナン, and the southern tree is a camphor tree.