By analyzing the arrangement of leaves, their forms, and the shape of the stem, one can determine if there is a uniform pattern that forms about the central axis (the shoot). This pattern is called lateral (or transectional) symmetry and is best observed by looking down on the apex of the shoot.

      Shoots with radial symmetry have leaves borne with equivalent angles of divergence. There are an infinite number of possible planes through the apex that divide the shoot into equivalent mirror images. This type of symmetry is common in orthotropically growing shoots and those having spiral phyllotaxis.

       Bilaterally symmetrical shoots are often elliptical in shape. They often have four orthostichies, a result of decussate phyllotaxis, or they may have distichous phyllotaxis (two orthostichies). Only two planes will bisect the shoot into equivalent mirror images. These planes can divide the shoot axis either along the median or the transversal plane.

      The third type of lateral symmetry found in shoots is dorsiventral symmetry. In this case only the median plane bisects the shoot axis into equivalent mirror images. Dorsiventrally symmetrical shoots have a distinct top, the dorsal portion, and a distinct bottom, the ventral portion. Dorsiventrality is typical of plagiotropical shoots, like lateral branches and rhizomes. If a rhizome lies mainly above ground, it is said to be epitonic. If the majority of the rhizome lies below the surface, it is said to be hypotonic. The rhizomes of many plants, such as Iris, are dorsiventral until they become reproductive. The rhizome grows plagiotropically until ontogenetic (developmental) changes enable the plant to grow orthotropically. Once this occurs the symmetry changes to either radial or bilateral.

The diagram on the left is radial symmetry. There are an infinite number of planes that when divided give equal halves.

The middle diagram shows bilateral symmetry. There are only two planes that provide equal halves.

The diagram on the right shows dorsiventral symmetry. Here there is only one plane of symmetry. Notice there is a definite top and bottom.

Platyclades and Phylloclades

      A platyclade is a flattened stem that has all of the features of a normal stem including indeterminate growth and usually obvious nodes and internodes. The "vegetable tapeworm" Homalocladium sp. is one such plant. The plant known commonly as prickly pear cactus, Opuntia, is another. The symmetry of both of these examples is bilateral.

      Phylloclades are flattened branches with determinate growth that usually are not differentiated into marked nodes and internodes. Ruscus hypophyllum is an example of a plant having very leaf-like phylloclades. These stems produce lateral buds that give rise to both flowers and new leaves. The flattened stem with its increased surface area obviously maximizes photosynthesis.

Isophylly and Anisophylly

      Generally, shoots exhibit isophylly. That is, the leaves along a shoot have more or less equivalent form from one node to the next. Some shoots are anisophyllous; the leaves have two different forms that are found at alternating nodes along the stem.

      There are two types of anisophylly: lateral anisophylly, which occurs only on lateral shoots, and habitual anisophylly, which occurs on all shoots of the plant.

      Lateral anisophylly is common on lateral branches of conifers, such as Sequoia. The lateral branches of this tree are plagiotropic and have dorsiventral symmetry. Although the leaves are initiated in a spiral phyllotaxy they come to lie in the same plane by their unequal growth. The needle leaves that arise from the ventral surface of the shoot grow longer and twist in order to orientate themselves for maximum sun exposure. Acer platanoides is an interesting example of lateral anisophylly because the pairs of leaves found in the median plane are unequal in size but are symmetric while the pairs found in the transverse plane are equal in size but are unsymmetrical.

      The scale leaves found on Thuja occidentalis are habitually anisophyllous. The scales found on the dorsal and ventral surfaces are wider than those found on the flanks. This difference allows the branches to maintain their planar form and contributes to the plant's ability to optimized surface area for photosynthesis. Habitual anisophylly, also called autonomous anisophylly, is found in plants that are anisophyllous regardless of the position of the shoot. One striking example of this type of leaf asymmetry is found in the aquatic fern, Salvinia auriculata. This aquatic plant has laminate leaves that grow above the surface of the water and ventral leaves that are highly dissected and are completely submerged under the water.