Modular growth and function in the vascular cryptogam Lycopodium annotinum

Abstract

Lycopodium annotinum L. is a long-lived plant that consists of a series of annually produced segments, which can be aged; a 20-year life cycle can be synthesized from historical records of the plant’s past growth. Detailed analyses of the modular construction of the plant show elements of deterministic and opportunistic growth which provide a framework in which physiological processes can be interpreted. A balance between deterministic and opportunistic growth is achieved by the relationships in terms of structure, function and longevity, between a series of horizontally growing modules and a series of more ephemeral vertically oriented modules. Each annual horizontal segment has an increasing probability of mortality as it ages, yet the segments are organized into units with indefinite apical growth and proximal senescence. In contrast, each vertical module has the inverse relationship between age and the probability of mortality : the youngest segments always die first. The result is a plant with fixed structures for photosynthesis, spore production and nutrient and water uptake, but with a highly organized and mobile transport system.