What Are the Hard Spots on a Baobab Tree? A Closer Look at This Unique African Tree’s Bark

The baobab tree, also known as the “Tree of Life”, is one of the most iconic trees in Africa. These massive trees are characterized by their thick, bottle-shaped trunks and sparse canopy of twisted branches. One of the most distinctive features of baobab trees is the presence of hexagonal or polygonal patterns in their bark. These patches often have a harder, bumpy texture compared to the surrounding smooth bark. But what causes these unusual hard spots on baobab trees? Let’s take a closer look.

There are nine different species of baobab trees, six from Madagascar and three from continental Africa. Of these the most widespread and well-known is the African baobab (Adansonia digitata). These deciduous trees are found throughout the hot dry woodlands of Africa. Baobabs can grow enormously large, reaching heights of 5 to 30 meters and trunk diameters of 7 to 11 meters. Some individual baobab specimens are estimated to be over 2,000 years old!

The baobab’s barrel-like trunk has minimal tapering, giving it a swollen or bloated appearance. The bark is shiny, smooth and reddish-brown. As the tree ages, the bark becomes etched with deep rifts and furrows. But within these furrows, distinctive patterns start to emerge in the form of hard, bumpy patches. What causes this unique texture?

The Origins of the Baobab’s Bark Patterns

The hard spots visible on baobab bark are lenticels. Lenticels are pores or breaks in the outermost layer of a woody plant’s bark that allow for gas exchange. On baobab trees, these lenticels are raised and often polygon-shaped, surrounded by ridges or grooves in the bark.

Lenticels serve several important functions for the baobab

• Gas exchange – Lenticels allow oxygen to diffuse into the inner living tissues of the tree while releasing carbon dioxide and water vapor. This is crucial for respiration and photosynthesis.

• Moisture regulation – By releasing water vapor, lenticels help regulate moisture levels in the tree and prevent overheating. This adaptation helps baobabs survive in hot, arid climates.

• Wound healing – When cracks form in the outer bark from damage or stress, new lenticels will develop during the healing process This results in thicker, harder patches.

As a baobab tree increases in age and size, the outer bark becomes increasingly grooved and folded. More lenticels form within these furrows, creating interesting geometric patterns in the bark. The lenticels also grow larger and become raised and hardened.

The Unique Structure of Baobab Bark

What makes baobab lenticels so pronounced compared to other trees? This comes down to the unique structure and composition of the baobab’s protective outer bark.

Baobab bark consists of five distinct layers:

1. Epidermis – The thin, outermost layer of cells.

2. Phellem – Multiple layers of cork cells that provide a waterproof barrier.

3. Phellogen – The cork cambium, a single layer of meristem cells that divides to produce new cork cells.

4. Phelloderm – A layer of parenchyma cells that carries out metabolic functions.

5. Inner bark – Phloem and other tissues that transport nutrients.

As new phellem cork cells are produced by the phellogen layer, the outer bark becomes layered and ridged. Lenticels initially form in the epidermis layer, and as the surrounding cork thickens, they become more pronounced. The lenticels expand and the ridges around them widen, creating the baobab’s distinctive and ornate bark patterns.

The Significance of Baobab Tree Bark

The baobab’s bark plays several important ecological roles:

• Fire resistance – The thick, fire-resistant outer bark protects the living inner bark and vascular tissues. This allows baobabs to survive the naturally-occurring bushfires in Africa’s savannas.

• Drought tolerance – By storing water in its spongy wood and corky bark, the baobab can withstand long periods of drought. The ridged bark also channels rainwater down the trunk to the roots.

• Temperature regulation – The light color of the baobab’s bark reflects sunlight, while the lenticels release heat. This helps moderate the temperature of the living tissues underneath.

• Antimicrobial properties – The corky bark contains antifungal compounds that protect against pathogens. This is why hollowed baobab trunks were traditionally used to store water and grain without spoiling.

We can thank those wonderful hard spots on baobab trees for helping sustain some of the largest, longest-living plant species on the planet. Next time you’re in Africa, take a moment to admire the majestic baobab and appreciate the miracles happening within and beneath its textured bark. I know I’ll never look at tree bark the same way again!