All metabolic reactions produce heat.

Some plants generate excess heat.

Thermogenic plant - Wikipedia

Botanists are not completely sure why thermogenic plants generate large amounts of excess heat, but most agree that it has something to do with increasing pollination rates. The most widely accepted theory states that the endogenous heat helps in spreading chemicals that attract pollinators to the plant. [1]

For example, the Voodoo lily uses heat to help spread its smell of rotting meat. [2]

This smell draws in flies which begin to search for the source of the smell. As they search the entire plant for the dead carcass, they unknowingly pollinate the plant. [3]

Other theories state that the heat may provide a heat reward for the pollinator: pollinators are drawn to the flower for its warmth. This theory has less support because most thermogenic plants are found in tropical climates.

Yet another theory is that the heat helps protect against frost damage, allowing the plant to germinate and sprout earlier than otherwise. For example, the skunk cabbage generates heat, which allows it to melt its way through a layer of snow in early spring. 4]

The heat, however, is mostly used to help spread its pungent odor and attract pollinators.