A seed plant or spermatophyte (
lit.'seed plant'; from
Ancient Greekσπέρματος (spérmatos) 'seed', and φυτόν (phytón) 'plant'), also known as a phanerogam (taxon Phanerogamae) or a phaenogam (taxon Phaenogamae), is any
plant that produces
seeds. It is a category of
embryophyte (i.e. land plant) that includes most of the familiar land plants, including the
flowering plants and the
gymnosperms, but not
ferns,
mosses, or
algae.
The term phanerogam or phanerogamae is derived from the
Greekφανερός (phanerós), meaning "visible", in contrast to the term "cryptogam" or "
cryptogamae" (from
Ancient Greekκρυπτός (kruptós) 'hidden'), together with the
suffixγαμέω (gaméō), meaning "to marry". These terms distinguish those plants with hidden sexual organs (cryptogamae) from those with visible ones (phanerogamae).
Description
The extant spermatophytes form five divisions, the first four of which are classified as
gymnosperms, 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 genus Ginkgo,
The fifth extant division is the
flowering plants, also known as angiosperms or magnoliophytes, the largest and most diverse group of spermatophytes:
Angiosperms, the flowering plants, possess seeds enclosed in a
fruit, unlike gymnosperms.
In addition to the five living taxa listed above, the fossil record contains evidence of many
extinct 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 late
Paleozoic.
Glossopteris was the most prominent tree genus in the ancient southern supercontinent of
Gondwana during the
Permian period.
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.[2] This gave rise to a series of evolutionary changes that resulted in the origin of modern 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.[3]
The spermatophytes were traditionally divided into
angiosperms, or flowering plants, and
gymnosperms, 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 on
vessel elements. However, molecular studies (and some more recent morphological[7][8] and fossil[9] 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:[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. Retrieved March 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.