The
plantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
division
Gnetophyta or gnetophytes comprise three related families of
woody plantA woody plant is a plant that uses wood as a structural tissue. They are typically perennial plants that have their stems and larger roots reinforced with wood produced adjacent to the vascular tissues: typically the main stem and larger branches and roots are covered by a layer of thickened bark....
s grouped in the
gymnospermGymnosperm is a group of spermatophyte seed-bearing plants with ovules on scales, which are usually arranged in cone-like structures....
s. The gnetophytes differ from other gymnosperms in having
vessel elementA vessel element is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are typically found in the angiosperms but absent from most gymnosperms such as the conifers....
s as in the
flowering plantThe flowering plants or angiosperms are the most diverse group of land plants. The flowering plants and the gymnosperms are the only extant groups of seed plants...
s.
The living Gnetophyta comprise three genera:
- Gnetum
Gnetum is a genus of about 30-35 species of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms they possess vessel elements in the xylem....
- Welwitschia
Welwitschia is a monotypic genus of gymnosperm plant, composed solely of the very distinct Welwitschia mirabilis. It is the only genus of the family Welwitschiaceae, in the order Welwitschiales, in the division Gnetophyta...
- Ephedra
Ephedra is a genus of gymnosperm shrubs, the only genus in the family Ephedraceae and order Ephedrales. These plants occur in dry climates over a wide area mainly in the northern hemisphere, across southern Europe, north Africa, southwest and central Asia, southwestern North America, and, in the...
GnetumGnetum is a genus of about 30-35 species of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms they possess vessel elements in the xylem....
species are mostly
woodWood is an organic material; in the strict sense wood is produced as secondary xylem in the stems of trees . In a living tree it transfers water and nutrients to the leaves and other growing tissues, and has a support function, enabling woody plants to reach large sizes or to stand up for themselves...
y
climbersThe term vine may refer to a climbing or trailing plant. The word, derived from Latin vīnea, in the original sense referred to the grapevines . The modern extended sense is mostly restricted to North American English, which uses "grapevine" to refer to the grape-bearing Vitis species...
in tropical forests. However, the most well-known member of this group,
Gnetum gnemonGnetum gnemon is a species of Gnetum native to southeast Asia and the western Pacific Ocean islands, from Assam south and east through Indonesia and Malaysia to the Philippines and Fiji...
, is a tree. Its seeds are used to produce a crispy
krupuk snack known as
emping or
krupuk belinjo.
WelwitschiaWelwitschia is a monotypic genus of gymnosperm plant, composed solely of the very distinct Welwitschia mirabilis. It is the only genus of the family Welwitschiaceae, in the order Welwitschiales, in the division Gnetophyta...
comprises only one species,
Welwitschia mirabilis. It grows only in the deserts of
NamibiaNamibia, officially the Republic of Namibia , is a country in Southern Africa whose western border is the Atlantic Ocean. It shares borders with Angola and Zambia to the north, Botswana and Zimbabwe to the east, and South Africa to the south and east...
and
AngolaAngola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean. The exclave province of Cabinda has a border with the Republic of the...
. The plant is strange in having only two large strap-like leaves for all its life. These grow continuously from the base, and are usually tattered at the ends by flapping in the winds.
Plants of the genus
EphedraEphedra is a genus of gymnosperm shrubs, the only genus in the family Ephedraceae and order Ephedrales. These plants occur in dry climates over a wide area mainly in the northern hemisphere, across southern Europe, north Africa, southwest and central Asia, southwestern North America, and, in the...
are known as jointfirs because they have long slender branches which bear tiny scale-like leaves at their nodes.
Ephedra has been traditionally used as a
stimulantStimulants, also sometimes called psychostimulants, are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others...
, but is a
controlled substanceA controlled substance is generally a drug or chemical whose manufacture, possession, and use are regulated by a government. This may include illegal drugs and prescription medications ....
today in many jurisdictions because of the risk of harmful or even fatal overdosing.
In some classifications all three genera are placed in a single order (Gnetales) but in others distributed among three orders, each containing a single family and genus.
Gnetum and
Welwitschia diverged from each other more recently than from
Ephedra.
Knowledge of fossils of the gnetophytes has increased greatly since the 1980s. There are fossils from the
PermianThe Permian
[The term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named...]
, the
TriassicThe Triassic is a geologic period and system that extends from about 251 to 199 Ma . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, and the
JurassicThe Jurassic is a geologic period and system that extends from about Ma to Ma, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Reptiles". The start of the period is marked by...
which may belong to the gnetophytes, but this is uncertain. The fossil record is richer starting in the early
CretaceousThe Cretaceous , Latin language for "chalky", usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period of the...
, with fossils of plants as well as
seedA seed , referred to as a kernel in some plants, is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s and
pollenPollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the...
which can be clearly assigned to the gnetophytes.
Molecular phylogenies of extant gymnosperms have conflicted with morphological characters with regard to whether the gymnosperms as a whole (including gnetophytes) comprise a monophyletic group or a paraphyletic one that gave rise to angiosperms. At issue is whether the Gnetophyta are the sister group of angiosperms, or whether they are sister to, or nested within, other extant gymnosperms. Numerous fossil gymnosperm clades once existed that are morphologically at least as distinctive as the four living
gymnospermGymnosperm is a group of spermatophyte seed-bearing plants with ovules on scales, which are usually arranged in cone-like structures....
groups, such as
BennettitalesBennettitales is an extinct order of seed plants that first appeared in the Triassic period and became extinct toward the end of the Cretaceous...
,
Caytonia and the glossopterids. When these gymnosperm fossils are considered the question of gnetophyte relationships to other seed plants becomes even more complicated.