An extract from which part of the plant was traditionally used to produce marshmallows?

The word "marshmallow" comes from the mallow plant species (Althaea officinalis), a herb native to parts of Europe, North Africa, and Asia which grows in marshes and other damp areas. The plant's stem and leaves are fleshy, and its white flower has five petals. It is not known exactly when marshmallows were invented, but their history goes back as early as 2000 BCE. Ancient Egyptians were said to be the first to make and use the root of the plant to soothe coughs and sore throats and to heal wounds. The first marshmallows were prepared by boiling pieces of root pulp with honey until thick. Once thickened, the mixture was strained, cooled, then used as intended.