Gunnerales
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The Gunnerales are an
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
of
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s. In the
APG III The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy being developed by the Angiosperm Phylogeny Group (APG). Published in 2009, it was superseded in 2016 by a fur ...
(2009) and
APG IV system The APG IV system of flowering plant classification is the fourth version of a modern, mostly molecular-based, system of plant taxonomy for flowering plants (angiosperms) being developed by the Angiosperm Phylogeny Group (APG). It was publish ...
s (2016), the order contains two
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
: '' Gunnera'' (
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Gunneraceae) and '' Myrothamnus'' (
Myrothamnaceae ''Myrothamnus'' is a genus of flowering plants, consisting of two species of small xerophytic shrubs, in the southern parts of tropical Africa and in Madagascar. ''Myrothamnus'' is recognized as the only genus in the family Myrothamnaceae. Myro ...
). In the
Cronquist system The Cronquist system is a list of systems of plant taxonomy, taxonomic classification system of angiosperms, flowering plants. It was developed by Arthur Cronquist in a series of monographs and texts, including ''The Evolution and Classification of ...
(1981), the Gunneraceae were in the Haloragales and Myrothamnaceae in the Hamamelidales.
DNA analysis Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...
proved definitive, but the grouping of the two families was a surprise, given their very dissimilar morphologies. In the older systems of Cronquist (1981, 1988) and Takhtajan (1997), the Gunneraceae were in the Rosidae, and the Myrothamnaceae were in the Hamamelids. In modern
classification systems Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...
, such as APG III and APG IV, this order was the first to diverge from the core
eudicots The eudicots or eudicotyledons are flowering plants that have two seed leaves (cotyledons) upon germination. The term derives from ''dicotyledon'' (etymologically, ''eu'' = true; ''di'' = two; ''cotyledon'' = seed leaf). Historically, authors h ...
. Some of the oldest fossils come from fossils dating the
Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...
stage in places like
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
,
Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...
and
Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
with these early pollen samples being known as ''Tricolpites''. At that time those landmasses were part of the continent known as
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
.


Description

Both families contain
ellagic acid Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid. Name The name comes from the French term ''acide ellagique'', from the word ''galle'' spelled backward because it can be o ...
.
Phloem Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is ...
cells contain a large number of
plastid A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria. Examples of plastids include chloroplasts ...
s and the leaves have dented borders. The plants are
dioecious Dioecy ( ; ; adj. dioecious, ) is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is ...
and possess small flowers without
perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower. It is a structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals) or tepal ...
, and the stigma is, at least weakly,
secretory Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical mec ...
. Gunnerales characters shared with the core eudicots are cyanogenesis via
phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the chemical formula, formula . It can be viewed as a benzyl group substituent, substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of ...
, metabolic pathways of
isoleucine Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the depro ...
or
valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deproton ...
, presence of the DNA sequence of PI-dB motif, and is common to have a small deletion in the sequence of 18S
ribosomal Ribosomes () are macromolecular machines, found within all cells, that perform biological protein synthesis (messenger RNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA molecules to fo ...
DNA. The characters which it shares with the core eudicots, and also with Buxales and Trochodendrales, are an absence of benzylisoquinoline alkaloids, ''euAP3'' + ''TM6'' genes (gene duplication ''paleoAP3'': Class B), and a loss of the
mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...
l gene '' rps2''.


Ecology

Despite being related, the
Myrothamnaceae ''Myrothamnus'' is a genus of flowering plants, consisting of two species of small xerophytic shrubs, in the southern parts of tropical Africa and in Madagascar. ''Myrothamnus'' is recognized as the only genus in the family Myrothamnaceae. Myro ...
and the Gunneraceae look very different: * The Gunneraceae are a mesophilic herb (often oversized), and the hydathodes are well developed and secrete mucilage or perhaps a resinous coating. * The Myrothamnaceae are a reviviscent shrub of arid habitats, and the hydathodes are poorly developed and secrete plant resin. Both have flowers without perianth, but the details of pollen (e.g. Zavada and Dilcher see 1986 10, Wanntorp et al. 2004th 2004b 11 and 12) differ. In Wilkinson 2000 13 is a table of differences.


References


External links


Gunnerales
in Stevens, P. F. (2001 onwards)
Angiosperm Phylogeny Website
Version 7, May 2006. {{Taxonbar, from=Q21846 Angiosperm orders Dioecious plants