Underground stems

Stems that arise within the soil are called underground stems. They are stems, not roots, however much they look the part — they carry nodes, scale leaves and buds.

Underground stems carry out three jobs at once:

• vegetative reproduction;
• storing food;
• carrying the plant through an unfavourable season.

The third explains the second. A plant that must sit out a dry or cold period loses everything above ground, so it packs a food store below it and starts again from that store when conditions return.

By their external characteristics, underground stems divide into four main types.