Marsileaceae
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2008-07-01T19:08:17Z
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{{Taxobox
| fossil_range = Lower [[Cretaceous]]<ref name="Yamada 2002" /> to recent
| name = Marsileaceae
| image = Illustration_Pilularia_globulifera0.jpg
| image_width = 240px
| image_caption = ''[[Pilularia]]'' (top) and ''[[Marsilea]]'' (bottom)
| regnum = [[Plant]]ae
| divisio = [[Pteridophyta]]
| classis = [[Pteridopsida]]
| ordo = [[Salviniales]]
| familia = '''Marsileaceae'''
| familia_authority = [[Charles-François Brisseau de Mirbel|Mirb.]]
| subdivision_ranks = Genera
| subdivision =
*''[[Marsilea]]'' [[Carolus Linnaeus|L.]] (45 to 65 species)
*''[[Pilularia]]'' [[Carolus Linnaeus|L.]] (6 species)
*''[[Regnellidium]]'' (1 species)
*''[[Regnellites]]'' †
*''[[Rodeites]]'' †
}}
The '''Marsileaceae''' are a small [[family (biology)|family]] of [[heterosporous]] [[aquatic ecosystem|aquatic]] and semi-aquatic [[fern]]s, though at first sight they do not physically resemble other ferns. The group is commonly known as the "pepperwort family" or as the "water-clover family" because the [[leaf|leaves]] of the genus ''Marsilea'' superficially resemble the leaves of a [[four-leaf clover]] (a [[flower]]ing plant). Leaves of this fern have sometimes been used to substitute for clover leaves<ref name="Gifford and Foster" /> on [[Saint Patrick's Day]]. In all, the family contains 3 [[genus|genera]] and 50 to 80 species with most of those belonging to ''Marsilea''.<ref name="Johnson 1993">{{cite book | last=Johnson | first=David M. | year=1993 | chapterurl=http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10539 | chapter=Marsileaceae | pages=331-335 | title=Flora of North America north of Mexico | edition=volume 2 | location= New York & Oxford | publisher=Oxford University Press | isbn= 0-19-508242-7 }}</ref><ref name="Pryer 1999">{{cite journal | last=Pryer | first= Kathleen M. | year=1999 | title=Phylogeny of Marsileaceous Ferns and Relationships of the Fossil Hydropteris pinnata Reconsidered | url=http://www.pryerlab.net/publication/fichier203.pdf | format=pdf | journal=International Journal of Plant Sciences | volume= 160 | issue=5 | pages= 931–954 | doi=10.1086/314177 }}</ref>
==Natural history==
Members of the Marsileaceae are [[aquatic plant|aquatic]] or semi-aquatic. Plants often grow in dense clumps in [[mud]] along the shores of [[pond]]s or [[stream]]s, or they may grow submerged in shallow water with some of the leaves extending to [[buoyancy|float]] on the water surface. They grow in seasonally wet habitats, but survive the winter or dry season by losing their leaves and producing hard, [[desiccation]]-resistant reproductive structures.<ref name="Lellinger 1985">{{cite book | last=Lellinger | first=David B. | year=1985 | title= A Field Manual of the Ferns & Fern-Allies of the United States & Canada | pages=303-307 | location=Washington, D. C. | publisher=Smithsonian Institution | isbn=0-87474-602-7, 0-87474-603-5 }}</ref>
[[Image:Marsilea Bild0717.jpg|thumb|180px|left|An African species of ''[[Marsilea]]'' with floating leaves]]
There are only three living genera in the family Marsileaceae. The majority of species (about 45 to 70) belong to the genus ''[[Marsilea]]'', which grows world-wide in warm-[[temperate]] and [[tropical]] regions.<ref name="Johnson 1993" /><ref name="Pryer 1999" /> ''Marsilea'' can be distinguished from the other two genera by the presence of four leaflets on each leaf, although some species occasionally produce six leaflets per leaf. A second genus ''[[Regnellidium]]'' includes a single living species that grows only in southern [[Brazil]]<ref name="Lellinger 1985" /> and neighboring parts of [[Argentina]];<ref name="Pryer 1999" /> it has only two leaflets per leaf. The third genus ''[[Pilularia]]'' grows widely in temperate regions of both the northern and southern hemispheres.<ref name="Lellinger 1985" /> Its leaves do not subdivide into leaflets but are slender and tapered to a point, so that it is often overlooked and mistaken for a [[grass]]. There are only about six species known.<ref name="Pryer 1999" />
The closest relatives of the Marsileaceae are the [[Salviniaceae]], which are also aquatic and heterosporous.<ref name="Smith 2006">{{cite journal | last=Smith | first=Alan R.| coauthors= Kathleen M. Pryer, Eric Schuettpelz, Petra Korall, Harald Schneider, & Paul G. Wolf | year=2006 | title= A classification for extant ferns | url=http://www.pryerlab.net/publication/fichier749.pdf | format=PDF | journal=Taxon | volume= 55 | issue=3 | pages= 705–731 }}</ref><ref name="Kenrick and Crane">{{cite book | last=Kenrick | first=Paul | coauthors=Peter R. Crane | year=1997 | title=The Origin and Early Diversification of Land Plants: A Cladistic Study | pages=243-244 | location=Washington, D. C. | publisher=Smithsonian Institution Press | isbn=1-56098-730-8 }}</ref> However, both of these other fern families float freely on the surface of ponds or lakes instead of rooting in soil or mud. The close relationship of these groups to the Marsileaceae is supported by both morphologic and molecular analysis,<ref name="Smith 2006"/> as well as by the discovery of an intermediate [[fossil]] named ''[[Hydropteris]]''.<ref name="Rothwell 1994">{{cite journal | last=Rothwell | first=G. W. | coauthors=R. A. Stockey | year=1994 | title=The role of ''Hydropteris pinnata'' gen. et sp. nov. in reconstructing the cladistics of heterosporous ferns | journal=American Journal of Botany | volume= 81 | issue=4 | pages= 479–492 | doi=10.2307/2445498 }}</ref> In general, the Salviniaceae and Azollaceae have a much better fossil record than the Marsileaceae.<ref name="Taylor and Taylor">{{cite book | last=Taylor | first=Thomas N. | coauthors=Edith L. Taylor | year=1993 | title=The Biology and Evolution of Fossil Plants | pages=434-435 | location= Englewood Cliffs, NJ | publisher= Prentice Hall | isbn= 0-13-651589-4 }}</ref> Until recently, ''[[Rodeites|Rodeites dakshinii]]'' was the oldest fossil member known; it is a preserved [[sporocarp (ferns)|sporocarp]] containing [[spore]]s, found in [[Tertiary]] [[chert]] of [[India]].<ref name="Taylor and Taylor" /> In 2000, the discovery of fossilized sporocarps from the [[Cretaceous]] of eastern [[North America]] was announced.<ref name="Lupia 2000">{{cite journal | last=Lupia | first=R. | coauthors= H. Schneider, G. M. Moeser, K. M. Pryer, & P. R. Crane | year=2000 | title= Marsileaceae Sporocarps and Spores from the Late Cretaceous of Georgia, U.S.A | url= http://www.pryerlab.net/publication/fichier200.pdf | format=PDF | journal= International Journal of Plant Sciences | volume=161 | issue=6 | pages=975–988 | doi= 10.1086/317567 }}</ref> These fossils were assigned to the species ''[[Regnellidium upatoiensis]]'', and pushed the known history of the Marsileaceae back into the [[Mesozoic]]. The oldest fossil known for the Marsileaceae is ''[[Regnellites|Regnellites nagashimae]]'' from the Upper [[Jurassic]] or Lower [[Cretaceous]] of [[Japan]].<ref name="Yamada 2002">{{cite journal| last= Yamada | first=Toshihiro | coauthors = Masahiro Kato | year=2002 | title=''Regnellites nagashimae'' gen. et sp. nov., the Oldest Macrofossil of Marsileaceae, from the Upper Jurassic to Lower Cretaceous of Western Japan | journal=International journal of Plant Science | volume=163 | issue=5 | pages=715–723 | doi=10.1086/342036 }}</ref> The fossils include leaves with visible veins, as well as sporocarps.
==Morphology==
The Marsileaceae share many of the basic structural characteristics common to most ferns, but the differences are more noticeable than the similarities. Species of this family have long, slender [[rhizome]]s that creep along or beneath the ground. Their [[frond]]s ([[leaf|leaves]]) grow in distinct clusters at [[Node (botany)|node]]s along the rhizome, with wide spacing between leaf clusters. As a result, the plants appear to be more stem than leaf, unlike other ferns.
[[Root]]s grow primarily from the same nodes as the leaves, but may also grow from other locations along the rhizome. The roots of ''Marsilea'' and ''Regnellidium'' are noteworthy for containing [[vessel element]]s. Vessels have also been found in the rhizome of two species of ''Marsilea''. These vessels have evolved independently of vessels in other groups of plants.<ref name="Gifford and Foster">{{cite book | last=Gifford | first=Ernest M. | coauthors=Adriance S. Foster | year=1988 | title=Morphology and Evolution of Vascular Plants | edition=3rd | pages=305-313 | location=New York | publisher=W. H. Freeman and Company | isbn=0-7167-1946-0 }}</ref>
[[Image:Marsilea Hawaii.jpg|thumb|180px|left|Leaves of the Hawaiian species ''Marsilea villosa'']]
The leaves are the most easily observed characteristic for the Marsileaceae; they have a long slender [[petiole (botany)|leaf stalk]] ending in zero, two, or four (occasionally six) leaflets. The number of leaflets differs among the three genera and can therefore be used for identification.<ref name="Pryer 1999" /> In ''Pilularia'', the leaves are narrowly cylindrical and taper to a point. Leaves of ''Regnellidium'' bear two broad leaflets, while leaves of ''Marsilea'' bear four leaflets at the tip. The four leaflets on the leaf of ''Marsilea'' are not borne equally. Instead, they are borne in pairs with one pair of leaflets attached slightly higher than the other.<ref name="Eames 1936">{{cite book | last=Eames | first=Arthur J. | year=1936 | title=Morphology of Vascular Plants (Lower Groups) | pages=197-223 | location=New York and London | publisher=McGraw-Hill Book Company }}</ref> Thus in the developing leaf, the leaflets are folded more like the wings of a [[butterfly]] than like the leaflets of a clover.
As with other ferns, the leaves develop in a '''[[vernation|circinate]]''' pattern.<ref name="Gifford and Foster" /> They begin as small, tight [[spiral]]s which unroll as the leaf matures. At full maturity they are held erect with the leaflets unfolded, except in ''Pilularia'' whose leaves have no blade. Temperate species are [[deciduous]], losing their vegetative leaves in [[winter]].<ref name="Johnson 1993" /> Tropical species may also lose their leaves during the [[dry season]]. These leaves are [[photosynthetic]], and produce most of the food used by the plant.
Some aquatic species of ''Marsilea'', especially those growing with their rhizome submerged, may have vegetative leaves that are [[frond dimorphism|dimorphic]]. Some of their leaves grow up to the surface of the water, and look just like leaves of species growing out of water. These plants also produce other leaves with shorter leaf stalks that are not long enough to reach the surface, and so the leaflets remain underwater. These leaves have different anatomical and [[cell (biology)|cellular]] characteristics better suited to their submerged environment.<ref name="Gifford and Foster" />
In addition to their vegetative ([[infertility|sterile]]) leaflets, all species of Marsileaceae produce [[fertile]] ([[spore]]-producing) leaflets at or near the base of the photosynthetic leaves. This reproductive portion looks and functions very differently from the vegetative portion of the leaves.
==Life cycle==
Like other ferns, members of the Marsileaceae produce [[spore]]s, but not [[seed]]s when they reproduce. Unlike other ferns, the spores in this family are produced inside '''[[sporocarp (ferns)|sporocarps]]'''. These are hairy, short-stalked, [[bean]]-shaped structures usually 3 to 8 [[millimetre|mm]] in diameter<ref name="Johnson 1993" /> with a hardened outer covering. This outer covering is tough and resistant to drying out, allowing the spores inside to survive unfavorable conditions such as winter frost or summer desiccation. Despite this toughness, the sporocarps will open readily in water if conditions are favorable, and specimens have been successfully [[germinate]]d after being stored for more than 130 years.<ref name="Moran 2004">{{cite book | last=Moran | first=Robin C. | year= 2004 | title=A Natural History of Ferns | pages=243-249 | location=Portland | publisher=Timber Press | isbn=0-88192-667-1 }}</ref> Each growing season, only one sporocarp typically develops per node along the rhizome near the base of the other leaf-stalks, though in some species of ''Marsilea'' there may be two or occasionally as many as twenty.<ref name="Campbell 1918" /><ref name="Eames 1936" /> The resemblance of the sporocarps to [[Black pepper|peppercorns]] gives the family its common name of ''pepperwort''.<ref name="Johnson 1993" />
[[Image:Pilularia globulifera - Thomé.jpg|thumb|180px|right|The European species ''[[Pilularia globulifera]]'' bearing [[sporocarp (ferns)|sporocarps]].]]
The sporocarps are functionally and developmentally modified leaflets,<ref name="Campbell 1918">{{cite book | last=Campbell | first=Douglas Houghton | year=1918 | title=The Structure and Development of Mosses and Ferns | edition=3rd | pages=417-439 | location=New York | publisher=The Macmillan Company }}</ref> although they have much shorter stalks than the vegetative leaflets. Inside the sporocarp, the modified leaflets bear several '''[[sorus|sori]]''', each of which consists of several [[sporangium|sporangia]] covered by a thin hood of tissue (the [[indusium]]). Each sorus includes a mix of two types of sporangium, each type producing only one of two kinds of spores. Toward the center of each sorus and developing first are the [[megasporangium|megasporangia]], each of which will produce a single large female [[megaspore]]. Surrounding them at the edge of the sorus and developing later are the [[microsporangium|microsporangia]], each of which will produce many small male [[microspore]]s.<ref name="Gifford and Foster" />
Because the Marsileaceae produce two kinds of spore (and thus two kinds of gametophyte), they are called '''[[heterosporous]]'''. While heterospory is the norm among all plants with seeds, such as the [[flowering plant]]s and [[conifer]]s, it is very rare among other groups of plants. Also, most heterosporous plants produce their two kinds of sporangia in different places on the plant. Since the Marsileaceae grow both kinds together in a single cluster, they differ from other plants in this regard as well.
The spores remain dormant inside the sporocarp through unfavorable conditions, but when conditions are suitable and wet, the sporocarp will germinate. It splits into halves, allowing the tissue coiled inside to become [[hydration|hydrated]]. As this internal tissue swells with water, it pushes the halves of the hard outer covering apart, and emerges as a long gelatinous worm-like '''sorophore'''. The sorophore is a sorus-bearing structure unique to the Marsileaceae; it may extend to more than ten times the length of the sporocarp inside which it was coiled. This extension carries the numerous spore-producing sori attached along each side of the sorophore out into the water.<ref name="Gifford and Foster" /><ref name="Campbell 1918" />
==Human uses==
Some species of ''Marsilea'' are cultivated in [[garden]] pools or [[aquarium|aquaria]].<ref name="Lellinger 1985" /> The [[Indigenous Australians]] once made a [[porridge]] of pulverized ''Marsilea'' sporocarps called ''[[Marsilea|nardoo]]''. However, the sporocarps contain toxic levels of [[thiaminase]], so careful preparation methods must be used in order for the ''nardoo'' to be safe for consumption.<ref name="Moran 2004" />
==References==
{{Reflist|2}}
==External links==
{{commonscat|Marsileaceae}}
*[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10539 Marsileacae description in the ''Flora of North America'']
*[http://www.csdl.tamu.edu/FLORA/cgi/b98_map?family=Marsileaceae Diversity map for US species]
*[http://www.pryerlab.net/publication/fichier200.pdf Lupia ''et al''. article describing Cretaceous fossils of Marsileaceae]
[[Category:Plant families]]
[[Category:Pteridophyta]]
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