The cactus is hailed as a "miracle in the desert", as most plants cannot survive in deserts, yet the cactus stands tall amidst the vast sea of sand. The forms of cacti we observe vary greatly, some are round, some are flat, some stand upright like poles, and some accumulate to resemble a mountain.

A unique feature of cacti among plants is their lack of traditional leaves, replaced entirely by spines. But why is this the case?

Cacti are currently distributed widely around the world, with the majority found in the arid deserts and semi-desert regions of tropical and subtropical America. Deserts are known for their scarce rainfall, but despite this, cacti thrive and become symbols of hope in these harsh environments. Even though cacti exhibit remarkable resilience, they still require water to sustain life, and their spines play a crucial role in this.

In most plants, leaves are the primary organs for photosynthesis. However, photosynthesis faces challenges in desert environments: high temperatures and high rates of evaporation exacerbate water loss, and plants need to close their stomata to reduce water loss, thereby limiting photosynthesis. Therefore, cacti have evolved a unique solution: they predominantly grow spines and scarcely grow leaves.

Rainfall in deserts is extremely uneven throughout the year, with heavy downpours during rainy seasons and almost no rain during dry seasons. Moreover, desert soils have poor water retention capabilities, resulting in severe water scarcity. To adapt to such harsh conditions, cacti have evolved from having leaves to having spines and hair-like structures, which help reduce water evaporation.

Studies show that while cacti have extensive root systems, these typically spread wide rather than deep. This rooting pattern allows cacti to absorb rainwater and dew over a wide area.

For example, a cactus 1.2 meters tall might have roots that spread only about 10 centimeters deep but extend outward for more than 5 meters. Furthermore, most of their roots are fibrous, readily absorbing water upon contact. Additionally, their roots are unusually swollen and capable of storing large amounts of water to cope with arid conditions.

Apart from these functions, cactus spines also have other remarkable properties:

1. Temperature regulation: Cactus spines can help regulate the plant's surface temperature, preventing overheating during the day and maintaining a certain temperature at night.

2. Seed dispersal assistance: Some cactus spines bear fine hairs or structures that can capture moisture from the air and direct it to the surface of the plant, providing water for seed germination.

The ability of cacti to survive and reproduce in extreme desert environments is closely tied to their long evolutionary history. Throughout evolution, individuals who could adapt to drought conditions and protect themselves from herbivores gradually became predominant. Eventually, these adaptive traits were inherited and fixed, resulting in the unique appearance and ecological role of modern cacti.

Therefore, the lack of leaves and predominance of spines in cacti are the results of their ecological adaptation to arid environments, shaped by evolution. In the desert, cacti stand as unique entities in the ecosystem, showcasing the marvel and diversity of nature.