Taxonomy is the science of classification and includes the following main aspects:
- Grouping. The assignment of individual organisms to groups based on their relatedness.
- Ranking. The assignment of groups to successively more inclusive ranks (species, genus, family, order etc). Ranks are extremely useful for navigating biodiversity information. However, it should be borne in mind that ranks are largely arbitrary and purely for the convenience of the user. Comparing taxa at the same rank as if they have some biological equivalence should be done cautiously if at all. This point has led some to reject ranks entirely (see phylocode) although others see this as an over-reaction.
- Naming. The application of rules to give universally accepted and stable names to groups. These names allow information about organisms to be readily retrievable ("biodiversity informatics") and they allow all biological investigations to be meaningful and repeatable.
Seed plants are those plants that are not free-sporing. The female spore (megaspore) is retained within a complex maternal structure, the ovule, in which it germinates to produce an embryosac (female gametophyte). A seed is the term used for a fertilised ovule. Seeds are a key innovation in plant evolution allowing maternal resources to protect and nourish the embryo post-dispersal. Extant seed plants include the gymnosperms (cycads, gnetophytes, ginkgos and conifers) and angiosperms (flowering plants).