A species which can produce a large seed population, will be at an advantage in a competitive situation and many weeds are notable for producing large numbers of seeds (See Table). Perennial plants are not under the same pressure to produce large numbers of seeds and are less prolific than annuals. The ability to set seed on poorly developed or young plants is an advantage when unfavourable environmental conditions limit growth or prevent further development.

It is an advantage to continue flower production for a long time to take advantage of favourable conditions. This may be achieved by producing seed over a very large portion of the growing period, or by a spread of flowering within the population.

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