Genetics and evolution of leaf development

Leaves

 

Plants can have simple leaves, with just one blade, like Arabidopsis thaliana, or compound leaves, like most legumes.

 

What is a compound leaf?

 

A typical compound leaf, such as that of chick pea (Cicer arietinum), is pinnate (Figure 1, centre). It resembles a feather, with pairs of leaflets arranged along a central rib, called the rachis. Many legumes, such as the tropical flame tree, Royal Poinciana (Delonix regia), have bipinnate compound leaves. In this case, the central rachis supports lateral rachides in a pinnate arrangement. Each lateral rachis in turn bears tiny, pinnately-arranged leaflets (Figure 1, right).

 

 

Figure 1.  An Arabidopsis thaliana leaf (simple, left), a Cicer arietinum leaf (pinnate, middle) and a Delonix regia leaf (bipinnate, right).

 

The garden pea leaf (Pisum sativum) is a variant of the typical pinnate leaf (Figure 2). The most notable feature is that the distal structures are tendrils, which grasp on to nearby objects by coiling around them.  Stipules are the pair of small, leaflet-like organs found at the base of a leaf (see Figure 1). In pea, the stipules are unusually large and shaped like ears (Figure 2).

 

 

Figure 2.  Botanical illustration of a pea from the Flora Graeca (1806 – 1840).

 

An aside: James Edward Smith (1759-1828), founder and first president of the Linnean Society, who published the first six volumes of the Flora Graeca, lived in Norwich. His house still stands on Surrey Street, in the centre of town. For a fascinating account of the production of this flora, read The Flora Graeca Story by H. Walter Lack, Oxford University Press (1999).

 

 

 

 

 

 

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