The fourth group of plants is conifers, which are also known as gymnosperms.
Conifer, any member of the division Pinophyta, class Pinopsida, order Pinales, made up of living and fossil gymnospermous plants that usually have needle-shaped evergreen leaves and seeds attached to the scales of a woody bracted cone. Among living gymnosperm divisions, the conifers show little similarity to the Cycadophyta and Gnetophyta but share several vegetative and reproductive traits with the Ginkgophyta. Conifers are most abundant in cool temperate and boreal regions, where they are important timber trees and ornamentals, but they are most diverse in warmer areas, including tropical mountains.
The conifers are the most varied gymnosperms. The world’s oldest trees are the 5,000-year-old bristlecone pines (Pinus longaeva) of desert mountains in California and Nevada. The largest trees are the giant sequoias (Sequoiadendron giganteum) of the Sierra Nevada of California, reaching heights of more than 95 metres (312 feet) and weights of at least 2 million kilograms (4.4 million pounds; compared with 190,000 kilograms for the largest recorded blue whale). Wherever conifers grow, especially in temperate climates, one of these species is usually the tallest tree. In fact, the very tallest trees are the coast redwoods (Sequoia sempervirens) of coastal California, some of which are more than 110 metres (361 feet) tall.
The world’s smallest trees probably are also conifers: the natural bonsai cypresses (Cupressus goveniana) and lodgepole pines (Pinus contorta) of the pygmy forests (adjacent to the towering redwood forests) of the northern California coasts. On the sterile hardpan soils of those astounding forests, the trees may reach full maturity at under 0.2 metre (0.7 foot) in height, while individuals of the same species on richer, deeper soils can grow to more than 30 metres (98 feet). Other conifers, such as the pygmy pine (Lepidothamnus laxifolius) of New Zealand, the smallest conifer, are always shrubby and may mature as shorter plants (less than 8 centimetres [3.15 inches] in height) than the pygmy cypress, but with greater spread.