seed Seeds and
spores can be used for reproduction (e.g.
sowing). Seeds are typically produced from
sexual reproduction within a species because
genetic recombination has occurred. A plant grown from seeds may have different characteristics from its parents. Some species produce seeds that require special conditions to germinate, such as
cold treatment. The seeds of many
Australian plants and plants from southern
Africa and the
American west require smoke or fire to germinate. Some plant species, including many
trees, do not produce seeds until they reach maturity, which may take many years. Seeds can be difficult to acquire, and some plants do not produce seed at all. Some plants (like certain plants modified using
genetic use restriction technology) may produce seed, but not a fertile seed. In certain cases, this is done to prevent the accidental spreading of these plants, for example by birds and other animals. ==Asexual propagation==