Marsileaceae
Marsileaceae Temporal range:
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Pilularia (top) and Marsilea (bottom) | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Division: | Polypodiophyta |
Class: | Polypodiopsida |
Order: | Salviniales |
Family: | Marsileaceae Mirb. |
Genera | |
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Marsileaceae (
Natural history
Members of the Marsileaceae are aquatic or semi-aquatic. Plants often grow in dense clumps in mud along the shores of ponds or streams, or they may grow submerged in shallow water with some of the leaves extending to 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.[3]
There are only three living genera in the family Marsileaceae. The majority of species (about 45 to 70) belong to the genus
The closest relatives of the Marsileaceae are the Salviniaceae, which are also aquatic and heterosporous.[4][5] 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,[4] as well as by the discovery of an intermediate fossil named Hydropteris.[6] In general, the Salviniaceae and Azollaceae have a much better fossil record than the Marsileaceae.[7] Until recently, Rodeites dakshinii was the oldest fossil member known; it is a preserved sporocarp containing spores, found in Tertiary chert of India.[7] In 2000, the discovery of fossilized sporocarps from the Cretaceous of eastern North America was announced.[8] These fossils were assigned to the species Regnellidium upatoiensis, and pushed the known history of the Marsileaceae back into the Mesozoic. Other remains include Regnellites nagashimae from the Upper Jurassic or Lower Cretaceous of Japan.[9] The fossils include leaves with visible veins, as well as sporocarps. The currently oldest known member of the family is Flabellariopteris, described in 2014 from isolated leaves dating to the Late Triassic in Liaoning, China.[10]
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
Roots 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 elements. 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.[11]
The leaves are the most easily observed characteristic for the Marsileaceae; they have a long slender 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.[2] 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.[12] 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
Some aquatic species of Marsilea, especially those growing with their rhizome submerged, may have vegetative leaves that are 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 cellular characteristics better suited to their submerged environment.[11]
In addition to their vegetative (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
The sporocarps are functionally and developmentally modified leaflets,
Because the Marsileaceae produce two kinds of spore (and thus two kinds of gametophyte), they are called
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 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.[11][14]
Human uses
Some species of Marsilea are cultivated in garden pools or aquaria.[3] The Indigenous Australians once made a porridge of pulverized Marsilea sporocarps called 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.[13]
References
- ^ ISBN 0-19-508242-7.
- ^ S2CID 14073501.
- ^ ISBN 0-87474-603-5.
- ^ JSTOR 25065646. Archived from the original(PDF) on 2008-02-26.
- ISBN 1-56098-730-8.
- JSTOR 2445498.
- ^ ISBN 0-13-651589-4.
- S2CID 16981770.
- S2CID 84631686.
- S2CID 129560335.
- ^ ISBN 0-7167-1946-0.
- ^ ISBN 0-88275-459-9.
- ^ ISBN 0-88192-667-1.
- ^ a b c Campbell, Douglas Houghton (1918). The Structure and Development of Mosses and Ferns (3rd ed.). New York: The Macmillan Company. pp. 417–439.