Vallisneria (named in honor of Antonio Vallisneri) is found all over the world and differ only slightly from each other with two exceptions; they are important plants in the aquarium hobby and one of the most widely used of all aquatic plants. They are as important as food to ducks, muskrats and other inhabitants that share their range which is nearly all fresh water. There is good evidence that Vallisneria originated in Australia.

Both annuals and perennials, the family are intriguing in a botanical sense because of the diverse morphology and multitude of reproductive systems. The family is primitively unisexual but has species with derived bisexual modes of reproduction: the plant can have both flowers on one or the other, and also have a unique mode of reproduction: a male flower at the base breaks off and floats to the surface where it releases pollen to the floating female flowers there and this is not uncommonly seen in aquaria.

While the reproduction has been studied in great detail taxonomy has not, the Linnean name Vallisneria spiralis was originally taken to apply to the plants on every continent. Eventually differences were noticed in the plant which prompted a revision of the genus (Svedelius 1932; Miki 1934; Kausik 1939). Later on more difference were found in North American, Australia and Asian species and another round of revision took place (Kadono 1994; Jacobs and Frank 1997; Haynes 2000).

In 1916 Rendell erected the genus Maidena for the Caulescent ("has a stem") species (V. caulescens, V. triptera) assigned specifically to Vallisneria (Bailey 1888; Jacobs and Frank 1997). Preliminary phylogenetic studies of Hydrocharitaceae have indicated that Maidenia probably is not distinct from Vallisneria (Les et al. 2006b); this today it is listed here as belonging in the genus.

Lowden in 1982 published a monograph placing all species into one of two taxa each with two varieties, however the differentiation of species was near impossible.

Les et. al. did the first phylogenetic treatment in 2008. Taxonomy here is based on this.

americana
americana

Grass-like

Lowden in 1982 published a monograph placing all species into one of two taxa each with two varieties, however the differemtiation of species was near imposstonl eand it di dot clinuee gthe uboresale spcies.


annua

Grass-like


asiatica
asiatica
biwaensis
asiatica

Grass-like


australis
Marmor
australis

Grass-like


caulescens
caulescens

Caulescent

Caulescent ("has a stem") species


denseserrulata

Grass-like


natans

Grass-like


neotropicalis

Grass-like


rubra
rubra

Caulescent

Caulescent ("has a stem") species


spinulosa

Grass-like


spiralis
spiralis

Grass-like


sp umbellate

Grass-like


triptera
triptera

Caulescent

Caulescent ("has a stem") species


Species in Genus : Vallisneria
References:

Lowden, R.M., 1982. An approach to the taxonomy of Vallisneria L. (Hydrocharitaceae). Aquat. Bot., 13: 269--298.



Abstract
Taxonomic decisions presented in this study of Vallisneria are founded on the consistency of comparable staminate and pistillate floral structures considering the geography and dioecious nature of the genus. Field studies, realized in southern Europe, eastern North America, Central America, northern South America and the Greater Antilles, formed the basis for the development of the present knowledge of characters. Umbel and spike-like inflorescences were discovered from three localities in the Americas. Staminodia were encountered in the female flowers of Vallisneria spiralis. Two species including four varieties are recognized, mapped and illustrated. Infraspecific taxa are V. spiralis L. vat. spiralis, V. spiralis var. denseserrulata Makino, V. americana Michaux var. americana and V. americana var. biwaensis (Miki) Lowden, comb. nov. These taxa are delineated according to the degree of connation of fertile filaments in the staminate flower and adnation of staminodia to stigma~style surfaces in the pistillate flower. Both species converge along what appears to be a continuous gradient in floral variation.
http://www.sciencedirect.com/science/article/pii/030437708290064X



Systematics of Vallisneria (Hydrocharitaceae)
Donald H. Les, Surrey W. L. Jacobs, Nicholas P. Tippery,1 Lei Chen, Michael L. Moody, and Maike Wilstermann-Hildebrand Systematic Botany (2008), 33(1): pp. 49–65



Abstract
Morphology, species delimitation, and interspecific relationships were evaluated in a phylogenetic context in the aquatic monocotyledon genus Vallisneria using a combination of morphological and molecular (nrITS, rbcL, trnK 5 intron) data. Contrary to previous studies that recognized few species worldwide, we distinguished 12 species by molecular data, and an additional 2–3 species by morphological differences within groups that were invariant at the molecular level. Two new Vallisneria species (V. australis, V. erecta) are formally described. Other potentially novel species were detected from the cultivated material examined but require further study to elucidate their taxonomic status. Phylogenetic analyses indicated that vittate (caulescent) species (including Maidenia rubra) are not basal, but nested between two groups of rosulate (rosette) species. To preserve Vallisneria as monophyletic, a new combination is made (V. rubra) that accommodates the transfer of M. rubra to Vallisneria. Several taxonomic characters associated with the stigma morphology of pistillate flowers were found to represent suites of features related to pollination. In most cases, these character suites corresponded to a particular arrangement of filaments in the staminate flowers. The precise geographical origin of Vallisneria remains difficult to determine. However, we conclusively documented the presence of the Old World V. spiralis in Texas (United States), which constitutes the first authentic record of this nonindigenous species in North America.
https://www.ingentaconnect.com/content/aspt/sb/2008/00000033/00000001/art00008