  We present a novel optimal allocation model for perennial plants, in which
assimilates are not allocated directly to vegetative or reproductive parts but
instead go first to a storage compartment from where they are then optimally
redistributed. We do not restrict considerations purely to periods favourable
for photosynthesis, as it was done in published models of perennial species,
but analyse the whole life period of a perennial plant. As a result, we obtain
the general scheme of perennial plant development, for which annual and
monocarpic strategies are special cases.
  We not only re-derive predictions from several previous optimal allocation
models, but also obtain more information about plants' strategies during
transitions between favourable and unfavourable seasons. One of the model's
predictions is that a plant can begin to re-establish vegetative tissues from
storage, some time before the beginning of favourable conditions, which in turn
allows for better production potential when conditions become better. By means
of numerical examples we show that annual plants with single or multiple
reproduction periods, monocarps, evergreen perennials and polycarpic perennials
can be studied successfully with the help of our unified model.
  Finally, we build a bridge between optimal allocation models and models
describing trade-offs between size and the number of seeds: a modelled plant
can control the distribution of not only allocated carbohydrates but also seed
size. We provide sufficient conditions for the optimality of producing the
smallest and largest seeds possible.
