Lithops, often called "living stones," are highly specialized succulent plants native to the arid deserts of southern Africa. Their survival hinges on a profound adaptation to extreme conditions, which includes entering distinct dormancy periods. From the plant's perspective, dormancy is not a choice but a vital, non-negotiable survival strategy to conserve resources during times of environmental stress, primarily intense heat and seasonal drought.
For many Lithops, the primary dormancy occurs during the peak of summer. From our perspective, the trigger is the combination of intense solar radiation and prolonged high temperatures. The plant's metabolism slows to a near standstill. Root activity ceases almost entirely to prevent water loss into the hot, dry soil. Above ground, the existing leaf pair stops growing and may even appear slightly shriveled as the plant draws on its internal moisture reserves. This is a deliberate state of suspended animation. The plant is effectively hiding, waiting out the most hostile period of the year when any attempt to grow would result in rapid desiccation and death. It is a patient, energy-conserving wait for the milder temperatures and life-giving rains that signal the end of this rest period.
Following a growth and flowering period in the autumn, many Lithops enter a slower, less pronounced dormancy in the deepest winter. The trigger here is the drop in temperature and reduced light levels. From the plant's viewpoint, this is a period of energy conservation and internal reorganization. The plant is not completely inactive; it is focused on a critical internal process: the development of a new leaf pair from the meristem tissue between the old leaves. The old leaves slowly sacrifice their stored water and nutrients to fuel this new growth. This rest period is crucial for the plant's annual renewal cycle. It allows the Lithops to recycle the resources from its old body to create a new one, all while minimizing external metabolic demands during a cool, often dry, season.
Our entire annual cycle is governed by environmental cues. The intensity and angle of sunlight, along with significant shifts in temperature, are the primary signals that initiate and conclude our dormancy. A decrease in photoperiod (day length) and a cooling trend tells us that the harsh summer is ending and it is time to wake up, flower, and grow. Conversely, lengthening days and rising heat signal the need to shut down. Any disruption to these cues, such as artificial watering during summer dormancy, sends a catastrophic mixed signal. It tricks our roots into activating, making them susceptible to rot in the warm, moist soil—a condition we are utterly unequipped to handle. Our survival is entirely dependent on a predictable cycle of stress and relief.
Internally, our dormancy is a complex physiological shift. The production of growth hormones like auxins and gibberellins is drastically reduced. Conversely, the concentration of abscisic acid (ABA), a hormone that induces dormancy and stomatal closure, increases. This hormonal shift ensures our stomata remain tightly sealed to prevent transpirational water loss. Cellular activity focuses on maintenance and repair rather than division and expansion. Energy resources are diverted from growth to the basic processes of keeping key tissues alive. This internal hibernation is the core of our strategy, allowing us to persist where other plants would perish.
