Patterns of thorn length, density, type and colour in African Acacias

Abstract

In Acacia no trade-off occurs between thorn length and thorn density and no correlation exists between thorn length and leaf length. By relating thorn length and density to leaf length it is clear that some species are better defended than others, with Acacia tortilis being best defended and A. caffra being most poorly defended. However, we note several factors suggesting that thorns are not primarily to protect leaves, but rather to protect stems. These are that spines occur in widely spaced pairs orientated around the stem, that they are white and that thorns are generally far shorter than leaves.

Keywords:

• SPINESCENCE
• HERBIVORY
• ARCHITECTURE