Flowering plants, or angiosperms—described taxonomically as the division Magnoliophyta—are the largest grouping within the plant kingdom (Kingdom Plantae or Viridiplantae) in terms of the numbers of described species. Approximately 260,000 species of flowering plant have been named so far, constituting nearly 90% of all known species of plants. Even so, taxonomists describe many new species annually, and estimates of total angiosperm diversity reach as high as 400,000 species. There are about 450 families of flowering plants, displaying extremely diverse life histories and ecological adaptations. In addition to dominating plant biodiversity, angiosperms are the dominant photosynthetic organisms (primary producers) in most terrestrial ecosystems (an important exception to this rule are the boreal forests, which are often dominated by conifers).