From a botanical perspective, those potato-like growths at the base and within the root system of a ZZ Plant (Zamioculcas zamiifolia) are not true bulbs, tubers, or even roots. They are highly specialized underground stem structures known as rhizomes. This distinction is crucial, as stems and roots have fundamentally different biological functions and anatomical structures. The ZZ Plant has evolved these rhizomes as a primary survival strategy, making it exceptionally resilient in its native, drought-prone habitats of eastern Africa.
ZZ Plant rhizomes may resemble potatoes (which are tubers), but their internal organization is that of a stem. True roots absorb water and nutrients, while stems are designed for storage and transport. The rhizome is composed of nodes and internodes, and it can produce new shoots and roots from its nodes. Its thick, fleshy appearance is due to parenchyma cells packed with starches and water. This serves as a massive internal reservoir, allowing the plant to survive extended periods of drought by drawing on these stored resources. The rhizome also anchors the plant firmly in the soil.
The primary physiological role of the rhizome is as a storage organ. In the unpredictable climates where ZZ Plants originate, rainfall can be scarce and sporadic. During brief rainy seasons, the plant goes into a state of rapid growth, absorbing as much water and nutrients as possible through its roots. These resources are not all used immediately; a significant portion is converted into starch and transported to the rhizomes for long-term storage. When the soil dries out, the plant enters a dormant state and sustains itself by slowly metabolizing these stored starches, maintaining cellular function until the next water source becomes available.
Beyond storage, rhizomes are central to the ZZ Plant's strategy for vegetative reproduction and expansion. As the plant matures, the rhizome grows horizontally beneath the soil surface. From the nodes on the rhizome, it can generate new growth points that develop into vertical stems (the part we see above soil) and new root systems. This is how a single ZZ Plant gradually forms a larger clump. For plant propagators, these rhizomes can be divided, with each section containing at least one growth node capable of generating a whole new plant, making it an efficient method of asexual reproduction that preserves the genetic identity of the parent plant.
A healthy ZZ Plant rhizome should be firm to the touch and have a pale, creamy color, often with distinct tan or brown scales (modified leaves). It is normal for them to be visible at the soil surface or even push slightly above it as the plant matures. The most common issue arises from overwatering, which can cause the water-logged, anaerobic soil conditions that lead to rhizome rot. In this state, the rhizome becomes soft, mushy, and may turn dark brown or black. Understanding that these structures are water-storing stems explains their vulnerability to rot—they are not adapted to sit in constantly saturated soil.
