Thorns with leaves and flowers are found in

Phylloclade is a modification of

Stems of potato,ginger and turmeric are modified to

Mentha $(Mint)$ has one of the following:

The lateral branches originate from the basal and underground portion of the main stem,grow horizontally beneath the soil and then come out obliquely upward giving rise to leafy shoots.

What are the main functions of the stem?