An example of a thick stem is the edible stem of the Rhubarb plant.
it is thick
A mushroom or fungus typically fits this description, with the thin stem and thick cap at the top.
A tree is one example. The sunflower usually has a thick stem. Rhubarb is another (edible stalk) thick stemmed plant.
A tree and the woody stem is called the trunk
A trunk ;)
flower power
No, actually the stem of a cactus is adapted to store water. The thick stem allows cacti to survive in dry desert climates by storing water for extended periods of time.
The stem of a clinical thermometer is thick to allow for better heat conduction between the body and the thermometer bulb, ensuring an accurate temperature reading. A thicker stem also provides durability and strength to withstand repeated use.
the thick part
Perhaps a "tree trunk".
That is called a tuber.
The thick part of an underground stem like a potato is called a tuber. Tuber is a storage organ that stores nutrients and energy for the plant to use for growth and reproduction.