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.

[12][13] The radiation of gymnosperms during the late Carboniferous appears to have resulted from a whole genome duplication event around 319 million years ago.

[14] Early characteristics of seed plants are evident in fossil progymnosperms of the late Devonian period around 383 million years ago.

The scorpionflies likely engaged in pollination mutualisms with gymnosperms, long before the similar and independent coevolution of nectar-feeding insects on angiosperms.

[15][16] Evidence has also been found that mid-Mesozoic gymnosperms were pollinated by Kalligrammatid lacewings, a now-extinct family with members which (in an example of convergent evolution) resembled the modern butterflies that arose far later.

[17] All gymnosperms are perennial woody plants,[18] Unlike in other extant gymnosperms the soft and highly parenchymatous wood in cycads is poorly lignified,[19] and their main structural support comes from an armor of sclerenchymatous leaf bases covering the stem,[20] with the exception of species with underground stems.

[21] There are no herbaceous gymnosperms and compared to angiosperms they occupy fewer ecological niches, but have evolved both parasites (Parasitaxus), epiphytes (Zamia pseudoparasitica) and rheophytes (Retrophyllum minus).

[22] Conifers are by far the most abundant extant group of gymnosperms with six to eight families, with a total of 65–70 genera and 600–630 species (696 accepted names).

[citation needed] Cycads, small palm-like trees,[2] are the next most abundant group of gymnosperms, with two or three families, 11 genera, and approximately 338 species.

[25] Ginkgo Cycas Dioon Bowenia Macrozamia Encephalartos Lepidozamia Ceratozamia Stangeria Microcycas Zamia Ephedra Gnetum Welwitschia Larix Pseudotsuga Pinus Cathaya Picea Cedrus Abies Keteleeria Pseudolarix Nothotsuga Tsuga Araucaria Agathis Wollemia Halocarpus Pectinopitys Prumnopitys Sundacarpus Lepidothamnus Phyllocladus Parasitaxus Lagarostrobos Manoao Saxegothaea Microcachrys Pherosphaera Acmopyle Dacrycarpus Dacrydium Falcatifolium Podocarpus Retrophyllum Afrocarpus Nageia Sciadopitys Cephalotaxus Amentotaxus Torreya Austrotaxus Pseudotaxus Taxus Cunninghamia Taiwania Athrotaxis Metasequoia Sequoiadendron Sequoia Cryptomeria Glyptostrobus Taxodium Papuacedrus Austrocedrus Libocedrus Pilgerodendron Callitris Neocallitropsis Widdringtonia Diselma Fitzroya Thuja Thujopsis Chamaecyparis Calocedrus Tetraclinis Microbiota Platycladus Juniperus Cupressus Hesperocyparis Xanthocyparis A formal classification of the living gymnosperms is the "Acrogymnospermae", which form a monophyletic group within the spermatophytes.

[2][34] The exception is the females in the cycad genus Cycas, which form a loose structure called megasporophylls instead of cones.

[38] The likely primary benefit of cross-pollination in gymnosperms, as in other eukaryotes, is that it allows the avoidance of inbreeding depression caused by the presence of recessive deleterious mutations.