We can hypothesize how Tmesipteris Leaves might have evolved.

Let us assume that we started with an Isotomous system of Telomes & Mesomes just like we did previously.

The first step would be the development of a stem system with unequal (Anisotomous) branching, so that a short shoot & a long shoot would develop at each dichotomy.

The next step would be similar to what we saw with Psilotum. The short Telomes could have expanded laterally to form a leaf blade.

This expansion could have continued until all of the short Telomes were Microphylls.

The angle between the Telomes and Mesomes could have become less than 45 degrees. This would result in a Pseudomonopodial system. Monopodial means one stem or axis. A stem with strong Apical Dominance like Araucaria (Norfolk Island Pine) or like Giant Sequoia would be good examples of a monopodial system.This is the result of Lateral Branching.

Anisotomous branching can lead to the formation of a structure which seems monopodial but does not have one main axis. The axis is actually composed of many short axes. The Mesomes form the Axis of the Pseudomonopodial system we are building.