camphor tree
楠 centers on the camphor tree, a specific large evergreen tree known for its aromatic wood and camphor oil.
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.
rhododendron
Rhododendron metternichii
Azuma rhododendron (Rhododendron metternichii var.)
Hakusan rhododendron (Rhododendron metternichii var.)
Tsukushi rhododendron (Rhododendron metternichii var.)
Kibana rhododendron (Rhododendron metternichii var.)