It is a fungus.
Lemon is neither an herb nor a shrub. It is a tree.
shrub
shrub
Shrubs
tree
Tree
A cucumber is a fruit (it contains seeds) but can also be classified as a vegetable.
Lemon plant is a tree, where the lemon fruits are growing. Those lemons, what we buy in grocery stores.
Technically it is called a herbaceous shrub
A bougainvillea is a shrub or small tree.
is bamboo a herb shrub or a tree