The termphanerogam orphanerogamae is derived from theGreekφανερός (phanerós), meaning "visible", in contrast to the term "cryptogam" or "cryptogamae" (from Ancient Greekκρυπτός (kruptós)'hidden', andγαμέω (gaméō), 'to marry'). These terms distinguish those plants with hidden sexual organs (cryptogamae) from those with visible ones (phanerogamae).
The extant spermatophytes form five divisions, the first four of which are classified asgymnosperms, plants that have unenclosed, "naked seeds":[1]: 172
Cycadophyta, the cycads, a subtropical and tropical group of plants,
Ginkgophyta, which includes a single living species of tree in the genusGinkgo,
The fifth extant division is theflowering plants, also known as angiosperms or magnoliophytes, the largest and most diverse group of spermatophytes:
Angiosperms, the flowering plants, possess seeds enclosed in afruit, unlike gymnosperms.
In addition to the five living taxa listed above, the fossil record contains evidence of manyextinct taxa of seed plants, among those:
Pteridospermae, the so-called "seed ferns", were one of the earliest successful groups of land plants, and forests dominated by seed ferns were prevalent in the latePaleozoic.
Glossopteris was the most prominent tree genus in the ancient southern supercontinent ofGondwana during thePermian period.
By theTriassic period, seed ferns had declined in ecological importance, and representatives of modern gymnosperm groups were abundant and dominant through the end of theCretaceous, when theangiosperms radiated.
A middleDevonian (385-million-year-old)precursor to seed plants fromBelgium has been identified predating the earliest seed plants by about 20 million years.Runcaria, small and radially symmetrical, is an integumentedmegasporangium surrounded by a cupule. Themegasporangium bears an unopened distal extension protruding above the mutlilobedintegument. It is suspected that the extension was involved in anemophilous (wind)pollination.Runcaria sheds new light on the sequence of character acquisition leading to the seed.Runcaria has all of the qualities of seed plants except for a solidseed coat and a system to guide the pollen to the seed.[3]
The spermatophytes were traditionally divided intoangiosperms, or flowering plants, andgymnosperms, which includes the gnetophytes, cycads,[5] ginkgo, and conifers. Older morphological studies believed in a close relationship between the gnetophytes and the angiosperms,[6] in particular based onvessel elements. However, molecular studies (and some more recent morphological[7][8] and fossil[9] papers) have generally shown aclade ofgymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as thegne-pine hypothesis and looks like:[10][11][12]
^Judd, Walter S.; Campbell, Christopher S.; Kellogg, Elizabeth A.; Stevens, Peter F.; Donoghue, Michael J. (2002).Plant systematics, a phylogenetic approach (2 ed.). Sunderland, Massachusetts: Sinauer Associates.ISBN0-87893-403-0.
^Jiao, Yuannian; Wickett, Norman J.; Ayyampalayam, Saravanaraj; et al. (2011). "Ancestral polyploidy in seed plants and angiosperms".Nature.doi:10.1038/nature09916.
^Gerrienne, P.; Meyer-Berthaud, B.; Fairon-Demaret, M.; Streel, M.; Steemans, P. (2011)."Science Magazine".Runcaria, A Middle Devonian Seed Plant Precursor.306 (5697). American Association for the Advancement of Science:856–858.doi:10.1126/science.1102491.PMID15514154.S2CID34269432.Archived from the original on February 24, 2011. RetrievedMarch 22, 2011.
^Coiro, Mario; Chomicki, Guillaume; Doyle, James A. (n.d.). "Experimental signal dissection and method sensitivity analyses reaffirm the potential of fossils and morphology in the resolution of the relationship of angiosperms and Gnetales".Paleobiology.44 (3):490–510.doi:10.1017/pab.2018.23.ISSN0094-8373.S2CID91488394.
Thomas N. Taylor, Edith L. Taylor, and Michael Krings. 2008.Paleobotany: The Biology and Evolution of Fossil Plants, 2nd edition. Academic Press (an imprint of Elsevier): Burlington, MA; New York, NY; San Diego, CA, USA, London, UK. 1252 pages.ISBN978-0-12-373972-8.
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