Annual versus Perennial?
Simply put, the difference between an annual and a perennial plant is that annuals survive for only one growing season while perennials survive into the next growing season. Annual and perennial plants have evolved different reproductive models that drive them into these classifications.
Annual plants have evolved from perennial ancestors and some annuals have even reverted to perennials over time. Common annuals include many food crops, flowers, and some weeds. The driving force behind the evolution of annual plants was likely harsh and uncertain growing conditions. Annual plants are well known for their life cycle of quick seed germination, fast vegetative growth, and rapid/profuse flower formation, senescence, and death. Rapid flower development is followed by seed production; and in harsh growing conditions rapid seed formation is essential for species survival and fitness. If a plant dies due to harsh conditions before it can produce seed, then no offspring will result. On a large scale this could lead to extinction. Annuals are essentially in a genetically induced race against time to reproduce.
Perennial plants have evolved a different survival and reproductive strategy than annuals. The perennial classification includes herbaceous plants like Rudbeckia spp. and woody plants like trees, shrubs, and woody vines. These plants are usually long lived and came-to-be in more certain growing conditions where their survival was not in doubt. Perennials can reproduce from seed, but may also reproduce from offshoots of the mother plant.
Seed formation and flowering occur more slowly in perennials as they cycle repeatedly between vegetative phases and flowering phases. This is one of the reasons why perennial flowering plants are deemed less florific than annuals.
Due to the slow growth of perennials, they can focus energy- that annuals use for rapid growth and seed formation- on the growth of extensive root structures, tubers, or bulbs. The extensive and deep root networks formed by perennials provide them access to water and nutrients that annuals cannot reach. These deep root systems combined with relatively slow growth allow perennials to store nutrients and increase their likelihood of longevity.