''Ruppia'', also known as the widgeonweeds, ditch grasses or widgeon grass, is the only extant genus in the family Ruppiaceae, with 11 known species. These are aquatic plants widespread over much of the world. The genus name honours Heinrich Bernhard Rupp, a German botanist (1688–1719). They are widespread outside of frigid zones and the tropics.

Description

The leaf is simple and not

rhizomatous In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

. They can be annual (commonly) or perennial (rarely); stem growth is conspicuously

sympodial In botany, sympodial growth is a bifurcating branching pattern where one branch develops more strongly than the other, resulting in the stronger branches forming the primary shoot and the weaker branches appearing laterally. A sympodium, als ...

, but sometimes is not. These species are adapted to be in

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

water (and salt marshes). The leaves are small or medium-sized. Their disposition can be alternate, opposite, or whorled (usually alternate except when subtending an inflorescence). Even, lamina keep entire and are setaceous or linear. The leaf just shows one vein without cross-venules. Stomata are not present. The mesophyll leaks calcium oxalate crystals. The minor leaf veins do not present phloem transfer cells and leaks vessels. These plants have stems without secondary thickening and xylem without vessels. The sieve-tube plastids are P-type. The root xylem does not present vessels. These plants are hermaphroditic, with anemophilous or hydrophilous pollination. The flowers are ebracteate, small, and regular. Commonly, the flowers are aggregated in ‘inflorescences’, but sometimes they are solitary. Often, they grow in racemes, spikes, or umbels. The scapiflorous inflorescences are terminal, in short spikes, or subumbelliform racemes, sometimes one- or few-flowered. They do not have hypogynous disks. These flowers do not have perianth absent, except when small staminal appendages are regarded as perianth segments. The androecial members are all equal. The androecium just presents two fertile stamens with sessile anthers dehiscing by longitudinal slits. The pollen is polysiphonous and its grains are three-celled and nonaperturate. The gynoecium (2–)4(−16) is superior, carpelled, and euapocarpous. The carpel is not stylate, apically stigmatic with the stigma peltate, or umbonate. These flowers only present one ovule pendulous, nonarillate, campylotropous, bitegmic, and crassinucellate. The placentation is apical and embryo-sac development is of the polygonum type. Before fertilization, they fuse polar nuclei. The fruit is drupaceous and fleshy, forming an aggregate. The fruiting carpel is indehiscent, commonly on a long, spirally twisted peduncle, with each drupelet becoming very long-stalked. The fruit contains one nonendospermic seed with starch. The embryo can be straight or slightly curved. Membranous testa do not have phytomelan.

Species

11 species are accepted. # '' Ruppia bicarpa'' – Western Cape, South Africa # '' Ruppia brevipedunculata'' – China (Jiangsu) # '' Ruppia cirrhosa'' (synonym '' Ruppia spiralis'') – temperate regions: Europe, Asia, north + south (but not tropical) Africa, North America, West Indies, Argentina. The name is a homotypic synonym of ''R. maritima''.Ito, Y., T. Ohi-Toma, C. Nepi, A. Santangelo, A. Stinca, N. Tanaka, & J. Murata (2017
Towards a better understanding of the ''Ruppia maritima'' complex (Ruppiaceae): Notes on the correct application and typification of the names ''R. cirrhosa'' and ''R. spiralis''
''

Taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

'' 66: 167–171 # '' Ruppia didyma'' – Mexico, West Indies # '' Ruppia drepanensis'' – western and central Mediterranean # '' Ruppia filifolia'' – southern South America, Falkland Islands # '' Ruppia maritima'' – seashores and lakeshores around the world # '' Ruppia megacarpa'' – Australia, New Zealand, Asia (Korea, Japan, and Russia)Ito, Y., T. Ohi-Toma, J. Murata & Nr. Tanaka (2010
Hybridization and polyploidy of an aquatic plant, ''Ruppia'' (Ruppiaceae), inferred from plastid and nuclear DNA phylogenies
''

American Journal of Botany The ''American Journal of Botany'' is a monthly peer-reviewed scientific journal which covers all aspects of plant biology. It has been published by the Botanical Society of America since 1914. The journal has an impact factor of 3.038, as of 20 ...

'' 97: 1156–1167Ito, Y., T. Ohi-Toma, A. V. Skriptsova, M. Sasagawa, Nr. Tanaka, and J. Murata (2014) ''Ruppia megacarpa'' (Ruppiaceae): a new species to the floras of Japan, Korea, and Russia. ''Botanica Pacofica'' 3: 49–52 # ''

Ruppia polycarpa ''Ruppia polycarpa'' is a submerged aquatic herb species in the genus ''Ruppia'' found in shallow brackish waters. It is a common submerged herb on Australasian coasts, including Australia (NSW; South Australia, SA; Vic, Spain, Vic; Western Aust ...

'' – Australia, New Zealand (including Chatham Islands) # '' Ruppia sinensis'' – China (Jiangsu) # '' Ruppia tuberosa'' – Australia

Taxonomy

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 ...

of 1981 placed the family in order Najadales of subclass Alismatidae in class Liliopsida monocotyledonsin division Magnoliophyta

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit. T ...

The

APG II system The APG II system (Angiosperm Phylogeny Group II system) of plant classification is the second, now obsolete, version of a modern, mostly Molecular phylogenetics, molecular-based, list of systems of plant taxonomy, system of plant taxonomy that ...

of 2003 (unchanged from the

APG system The APG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostly molecular-based, system of plant taxonomy. Published in 1998 by the Angiosperm Phylogeny Group, it was replaced by the improved ...

of 1998) does recognize such a family and places it in the order

Alismatales The Alismatales (alismatids) are an order of flowering plants including about 4,500 species. Plants assigned to this order are mostly tropical or aquatic. Some grow in fresh water, some in marine habitats. Perhaps the most important food cro ...

, in the clade

monocots Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are flowering plants whose seeds contain only one embryonic leaf, or cotyledon. A monocot taxon has been in use for several decades, but with various ranks a ...

. According to th
AP-Website
the family is doubtfully distinct from the family

Cymodoceaceae Cymodoceaceae is a family of flowering plants, sometimes known as the "manatee-grass family", which includes only marine species. The 2016 APG IV does recognize Cymodoceaceae and places it in the order Alismatales, in the clade monocots. The ...

: the plants in the three families

Posidoniaceae ''Posidonia'' is a genus of flowering plants. It contains nine species of marine plants (" seagrass"), found in the seas of the Mediterranean and around the south coast of Australia. The APG system (1998) and APG II system (2003) accept this ...

, and Ruppiaceae form a monophyletic group. A genus-level taxonomy was briefly revised by Zhao and Wu in 2008. Marine grasses families: Zosteraceae,

, Ruppiaceae and

. Related families:

Potamogetonaceae The Potamogetonaceae, commonly referred to as the pondweed family, is an aquatic family of monocotyledonous flowering plants. The roughly 110 known species are divided over five genera. The largest genus in the family by far is '' Potamogeton'', ...

, Zannichelliaceae (not consistently).

Phylogeny and evolution

The first molecular phylogeny of the monogeneric family discerned three distinct species, ''R''. ''tuberosa'', ''R''. ''megacarpa'', and ''R''. ''polycarpa'', and one species complex comprising six lineages. The species complex, named ''R''. ''maritima'' complex, was later updated as a group of eight lineages.Ito, Y., T. Ohi-Toma, J. Murata & Nr. Tanaka (2013
Comprehensive phylogenetic analyses of the ''Ruppia'' ''maritima'' complex focusing on taxa from the Mediterranean
'' Journal of Plant Research'' 126: 753–762 These studies revealed that multiple hybridization and

polyploidy Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

events as well as chloroplast capture have occurred in the evolution of the genus.

Phytochemistry

These plants present an anatomy non-C4 type. Seven labdanes have been identified from this genus: :* ''ent''-14,15-Dinor-8(17)-labden-13-one :* Methyl ester of (''ent-12S'')-15,16-Epoxy-12-hydroxy-12-oxo-8(17),13(16),14-labdatrien-19-oic acid. :* (-)-15,16-epoxy-8(17),13(16),14-labdatrien-19-ol. :* Methyl ester of (-)-15,16-epoxy-8(17),13(16),14-labdatrien-19-oic acid. :* (-)-15,16-Epoxy-8(17),13(16),14-labdatrien-19-al. :* (-)-15,16-Epoxy-8(17),13(16),14-labdatrien-19-yl acetate :* (''ent-13E'')-8(17),13-Labdadien-15-ol Three steroids have been also isolated: :* (''3β,5α,6β,7α,22E,24R'')-Ergosta-8(14),22-diene-3,6,7-triol. :* (3β,5α,6β,7α,22E,24R)-Ergosta-8,22-diene-3,6,7-triol :* (24R)-Ergost-4-ene-3,6-dione.

References

External links

Ruppiaceae in the ''Flora of North America''

NCBI Taxonomy Browser

links at CSDL, Texas
{{Authority control Brackish water plants Alismatales genera