Gymnosperm

Gymnosperm Temporal range: Carboniferous–Present PreꞒ Ꞓ O S D C P T J K Pg N
Various gymnosperms.
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Spermatophytes
Clade:	Gymnospermae
Living orders[1]
Cycadopsida Cycadales Ginkgoopsida Ginkgoales Pinopsida Cupressidae Araucariales Cupressales Pinidae Pinales Gnetopsida Ephedrales Welwitschiales Gnetales

The gymnosperms (/ˈdʒɪmnəˌspɜːrmz, -noʊ-/ ^ⓘ JIM-nə-spurmz, -⁠noh-; lit. 'revealed seeds') are a group of woody, perennial seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae^[2] The term gymnosperm comes from the composite word in Greek: γυμνόσπερμος (γυμνός, gymnos, 'naked' and σπέρμα, sperma, 'seed'), and literally means 'naked seeds'. The name is based on the unenclosed condition of their seeds (called ovules in their unfertilized state). The non-encased condition of their seeds contrasts with the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or on their own as in yew, Torreya, and Ginkgo.

The life cycle of a gymnosperm involves alternation of generations, with a dominant diploid sporophyte phase, and a reduced haploid gametophyte phase, which is dependent on the sporophytic phase.^[3] The term "gymnosperm" is often used in paleobotany to refer to (the paraphyletic group of) all non-angiosperm seed plants. In that case, to specify the modern monophyletic group of gymnosperms, the term Acrogymnospermae is sometimes used.^[4]

The gymnosperms and angiosperms together constitute the spermatophytes or seed plants. The spermatophytes are subdivided into five divisions, the angiosperms and four divisions of gymnosperms: the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta). Newer classification place the gnetophytes among the conifers.^[5] Numerous extinct seed plant groups are recognised including those considered pteridosperms/seed ferns, as well other groups like the Bennettitales.^[6]

By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). About 65% of gymnosperms are dioecious,^[7] but conifers are almost all monoecious.^[8] Some genera have ectomycorrhiza fungal associations with roots (Pinus),^[9] while in some others (Cycas) small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.^[10]