type of fruit tree
棯 refers to a type of fruit tree. The exact species is not specified in the given meanings, so treat it as a general tree that bears fruit.
棯 combines 木 (tree) with 念, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound for a type of tree.
The left side is a tree 木, and the right side 念 looks like a thought bubble over a heart. Picture a tree whose fruit is so delicious that just thinking about it makes your heart happy.
For ネン, imagine a fruit tree that bears fruit every year without fail: 'nen' sounds like 'annual' in the sense of a yearly cycle. The tree's yearly fruiting rhythm helps you remember ネン.