The spermatophytes (lit.'seed-bearing plants'; from Ancient Greekσπέρματος (spérmatos) 'seed', and φυτόν (phutón) 'plant'), also known as phanerogams (taxon Phanerogamae) or phaenogams (taxon Phaenogamae), comprise those plants that produce seeds, hence the alternative name seed plants. They are a subset of the embryophytes or land plants.
The term phanerogams or phanerogamae is derived from the Greekφανερός (phanerós), meaning "visible", in contrast to the cryptogamae (from Ancient Greekκρυπτός (kruptós) 'hidden'), together with the suffixγαμέω (gaméō), meaning "to marry". These terms distinguished those plants with hidden sexual organs (cryptogamae) from those with visible sexual organs (phanerogamae).
The extant spermatophytes form five divisions, the first four of which are traditionally grouped as gymnosperms, plants that have unenclosed, "naked seeds":: 172
Cycadophyta, the cycads, a subtropical and tropical group of plants,
By the Triassic period, seed ferns had declined in ecological importance, and representatives of modern gymnosperm groups were abundant and dominant through the end of the Cretaceous, when the angiosperms radiated.
A whole genome duplication event in the ancestor of seed plants occurred about 319 million years ago. This gave rise to a series of evolutionary changes that resulted in the origin of seed plants.
A middle Devonian (385-million-year-old) precursor to seed plants from Belgium has been identified predating the earliest seed plants by about 20 million years. Runcaria, small and radially symmetrical, is an integumented megasporangium surrounded by a cupule. The megasporangium bears an unopened distal extension protruding above the mutlilobed integument. 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 solid seed coat and a system to guide the pollen to the seed.
Relationships and nomenclature
Seed-bearing plants are a subclade of the vascular plants (tracheophytes) and were traditionally divided into angiosperms, or flowering plants, and gymnosperms, which includes the gnetophytes, cycads, ginkgo, and conifers. Older morphological studies believed in a close relationship between the gnetophytes and the angiosperms, in particular based on vessel elements. However, molecular studies (and some more recent morphological and fossil papers) have generally shown a clade of gymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as the gne-pine hypothesis and looks like:
An alternative phylogeny of spermatophytes based on the work by Novíkov & Barabaš-Krasni 2015 with plant taxon authors from Anderson, Anderson & Cleal 2007 showing the relationship of extinct clades.
^Judd, Walter S.; Campbell, Christopher S.; Kellogg, Elizabeth A.; Stevens, Peter F.; Donoghue, Michael J. (2002). Plant systematics, a phylogenetic approach (2 ed.). Sunderland MA, USA: Sinauer Associates Inc. ISBN 0-87893-403-0.
^Jiao Y, Wickett NJ, Ayyampalayam S, Chanderbali AS, Landherr L, Ralph PE, Tomsho LP, Hu Y, Liang H, Soltis PS, Soltis DE, Clifton SW, Schlarbaum SE, Schuster SC, Ma H, Leebens-Mack J, Depamphilis CW (2011) Ancestral polyploidy in seed plants and angiosperms. Nature
^"Science Magazine". Runcaria, a Middle Devonian Seed Plant Precursor. American Association for the Advancement of Science. 2011. Retrieved March 22, 2011.
^James A. Doyle (January 2006). "Seed ferns and the origin of angiosperms". The Journal of the Torrey Botanical Society. 133 (1): 169–209. doi:10.3159/1095-5674(2006)133[169:SFATOO]2.0.CO;2. ISSN 1095-5674.
^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. ISSN 0094-8373. S2CID 91488394.
^Zi-Qiang Wang (2004). "A New Permian Gnetalean Cone as Fossil Evidence for Supporting Current Molecular Phylogeny". Annals of Botany. 94 (2): 281–288. doi:10.1093/aob/mch138. PMC4242163. PMID15229124.
^Chaw, Shu-Miaw; Parkinson, Christopher L.; Cheng, Yuchang; Vincent, Thomas M.; Palmer, Jeffrey D. (2000). "Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers". Proceedings of the National Academy of Sciences. 97 (8): 4086–4091. Bibcode:2000PNAS...97.4086C. doi:10.1073/pnas.97.8.4086. PMC18157. PMID10760277.
^Soltis, Douglas E.; Soltis, Pamela S.; Zanis, Michael J. (2002). "Phylogeny of seed plants based on evidence from eight genes". American Journal of Botany. 89 (10): 1670–1681. doi:10.3732/ajb.89.10.1670. PMID21665594.
^Chung-Shien Wu, Ya-Nan Wang, Shu-Mei Liu and Shu-Miaw Chaw (2007). "Chloroplast Genome (cpDNA) of Cycas taitungensis and 56 cp Protein-Coding Genes of Gnetum parvifolium: Insights into cpDNA Evolution and Phylogeny of Extant Seed Plants". Molecular Biology and Evolution. 24 (6): 1366–1379. doi:10.1093/molbev/msm059. PMID17383970.CS1 maint: multiple names: authors list (link)
^Won, Hyosig; Renner, Susanne (August 2006). "Dating Dispersal and Radiation in the Gymnosperm Gnetum (Gnetales)—Clock Calibration When Outgroup Relationships Are Uncertain". Systematic Biology. 55 (4): 610–622. doi:10.1080/10635150600812619. PMID16969937.
^Novíkov & Barabaš-Krasni (2015). Modern plant systematics. Liga-Pres. p. 685. doi:10.13140/RG.2.1.4745.6164. ISBN 978-966-397-276-3.
^Anderson, Anderson & Cleal (2007). Brief history of the gymnosperms: classification, biodiversity, phytogeography and ecology. Strelitzia. 20. SANBI. p. 280. ISBN 978-1-919976-39-6.
Kron, Kathleen A; Chase, Mark W (2005-11-17). Molecular systematics and seed plant phylogeny: a summary of a parsimony analysis of rbcL sequence data. pp. 243–252. ISBN 9780521022897., in Gibbs et al (1995)
Gibbs, Adrian J.; Calisher, Charles H.; García-Arenal, Fernando, eds. (1995). Molecular basis of virus evolution. Cambridge: Cambridge University Press. ISBN 9780521022897.