Marsileaceae
Encyclopedia
The Marsileaceae are a small family
of heterosporous 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 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 on Saint Patrick's Day
. In all, the family contains 3 genera
and 50 to 80 species with most of those belonging to Marsilea.
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 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.
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 worldwide in warm-temperate
and tropical regions. 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
and neighboring parts of Argentina
; it has only two leaflets per leaf. The third genus Pilularia
grows widely in temperate regions of both the northern and southern hemispheres. 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.
The closest relatives of the Marsileaceae are the Salviniaceae
, which are also aquatic and heterosporous. 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, as well as by the discovery of an intermediate fossil
named Hydropteris. In general, the Salviniaceae and Azollaceae have a much better fossil record than the Marsileaceae. Until recently, Rodeites dakshinii
was the oldest fossil member known; it is a preserved sporocarp
containing spore
s, found in Tertiary
chert
of India
. In 2000, the discovery of fossilized sporocarps from the Cretaceous
of eastern North America
was announced. 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 nagashimae
from the Upper Jurassic
or Lower Cretaceous
of Japan
. The fossils include leaves with visible veins, as well as sporocarps.
s that creep along or beneath the ground. Their frond
s (leaves
) grow in distinct clusters at nodes 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.
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. 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. 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 circinate
pattern. 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. 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 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.
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.
s, but not seed
s when they reproduce. Unlike other ferns, the spores in this family are produced inside sporocarps
. These are hairy, short-stalked, bean
-shaped structures usually 3 to 8 mm in diameter 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 germinated after being stored for more than 130 years. 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. The resemblance of the sporocarps to peppercorns
gives the family its common name of pepperwort.
The sporocarps are functionally and developmentally modified leaflets, although they have much shorter stalks than the vegetative leaflets. Inside the sporocarp, the modified leaflets bear several sori
, each of which consists of several 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 megasporangia, each of which will produce a single large female megaspore
. Surrounding them at the edge of the sorus and developing later are the microsporangia, each of which will produce many small male microspore
s.
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 conifers, 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 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.
pools or aquaria
. 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.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of heterosporous aquatic
Aquatic ecosystem
An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....
and semi-aquatic fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
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 leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
of the genus Marsilea superficially resemble the leaves of a four-leaf clover
Four-leaf clover
The four-leaf clover is an uncommon variation of the common, three-leaved clover. According to tradition, such leaves bring good luck to their finders, especially if found accidentally...
(a flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
ing plant). Leaves of this fern have sometimes been used to substitute for clover leaves on Saint Patrick's Day
Saint Patrick's Day
Saint Patrick's Day is a religious holiday celebrated internationally on 17 March. It commemorates Saint Patrick , the most commonly recognised of the patron saints of :Ireland, and the arrival of Christianity in Ireland. It is observed by the Catholic Church, the Anglican Communion , the Eastern...
. In all, the family contains 3 genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and 50 to 80 species with most of those belonging to Marsilea.
Natural history
Members of the Marsileaceae are aquaticAquatic plant
Aquatic plants are plants that have adapted to living in aquatic environments. They are also referred to as hydrophytes or aquatic macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface. Aquatic plants can only grow in water or in soil that is...
or semi-aquatic. Plants often grow in dense clumps in mud
Mud
Mud is a mixture of water and some combination of soil, silt, and clay. Ancient mud deposits harden over geological time to form sedimentary rock such as shale or mudstone . When geological deposits of mud are formed in estuaries the resultant layers are termed bay muds...
along the shores of pond
Pond
A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...
s or stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s, or they may grow submerged in shallow water with some of the leaves extending to float
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
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
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
-resistant reproductive structures.
Marsilea
Marsilea is a genus of approximately 65 species of aquatic ferns of the family Marsileaceae.These small plants are of unusual appearance and do not resemble common ferns...
, which grows worldwide in warm-temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
and tropical regions. 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
Regnellidium
Regnellidium is a monotypic genus of ferns of family Marsileaceae.The single living species, Regnellidium diphyllum, Two-leaf Water Fern, is native to South Eastern Brazil and adjacent regions of Argentina. It resembles its relatives from the genus Marsilea, but has 2-lobed leaves . This fern is...
includes a single living species that grows only in southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
and neighboring parts of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
; it has only two leaflets per leaf. The third genus Pilularia
Pilularia
Pilularia is a genus of unusual ferns of family Marsileaceae distributed in North Temperate regions, Ethiopian mountains, and the southern hemisphere in Australia, New Zealand, and western South America....
grows widely in temperate regions of both the northern and southern hemispheres. 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
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
. There are only about six species known.
The closest relatives of the Marsileaceae are the Salviniaceae
Salviniaceae
Salviniaceae , is a family of ferns....
, which are also aquatic and heterosporous. 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, as well as by the discovery of an intermediate fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
named Hydropteris. In general, the Salviniaceae and Azollaceae have a much better fossil record than the Marsileaceae. Until recently, Rodeites dakshinii
Rodeites
Rodeites dakshinii is a fossil belonging to the fern family Marsileaceae. The fossil consists of a preserved sporocarp containing spores, and was recovered from a Tertiary chert of India....
was the oldest fossil member known; it is a preserved sporocarp
Sporocarp (ferns)
A sporocarp is a specialised type of structure found in some ferns whose primary function is the production and release of spores.Among ferns, sporocarps are found only in the three families of the order Salviniales, a group that is both aquatic and heterosporous. The term actually refers to two...
containing spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s, found in Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
of India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. In 2000, the discovery of fossilized sporocarps from the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
of eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
was announced. These fossils were assigned to the species Regnellidium upatoiensis, and pushed the known history of the Marsileaceae back into the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
. The oldest fossil known for the Marsileaceae is Regnellites nagashimae
Regnellites
Regnellites nagashimae is the oldest known fossil belonging to the fern family Marsileaceae. It comes from rocks of the Upper Jurassic or Lower Cretaceous of Japan. The fossils include leaves with visible veins, as well as sporocarps....
from the Upper Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
or Lower Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. 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 rhizomeRhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
s that creep along or beneath the ground. Their frond
Frond
The term frond refers to a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group...
s (leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
) grow in distinct clusters at nodes 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
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
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
Vessel element
A vessel element is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are typically found in the angiosperms but absent from most gymnosperms such as the conifers....
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.
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
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. 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. Thus in the developing leaf, the leaflets are folded more like the wings of a butterfly
Butterfly
A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured...
than like the leaflets of a clover.
As with other ferns, the leaves develop in a circinate
Vernation
Vernation is the formation of new leaves or fronds. In plant anatomy, it is the arrangement of leaves in a bud....
pattern. They begin as small, tight spiral
Spiral
In mathematics, a spiral is a curve which emanates from a central point, getting progressively farther away as it revolves around the point.-Spiral or helix:...
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
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
, losing their vegetative leaves in winter. Tropical species may also lose their leaves during the dry season
Dry season
The dry season is a term commonly used when describing the weather in the tropics. The weather in the tropics is dominated by the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year...
. 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 dimorphic
Frond dimorphism
Frond dimorphism refers to a difference in ferns between the fertile and sterile fronds. Since ferns, unlike flowering plants, bear spores on the leaf blade itself, this may affect the form of the frond itself...
. 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
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
characteristics better suited to their submerged environment.
In addition to their vegetative (sterile
Infertility
Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term...
) leaflets, all species of Marsileaceae produce fertile
Fertile
The term fertile describes a condition whereby organisms are able to produce physically healthy offspring.Fertile may also refer to:...
(spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
-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 sporeSpore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s, but not seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s when they reproduce. Unlike other ferns, the spores in this family are produced inside sporocarps
Sporocarp (ferns)
A sporocarp is a specialised type of structure found in some ferns whose primary function is the production and release of spores.Among ferns, sporocarps are found only in the three families of the order Salviniales, a group that is both aquatic and heterosporous. The term actually refers to two...
. These are hairy, short-stalked, bean
Bean
Bean is a common name for large plant seeds of several genera of the family Fabaceae used for human food or animal feed....
-shaped structures usually 3 to 8 mm in diameter 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 germinated after being stored for more than 130 years. 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. The resemblance of the sporocarps to peppercorns
Black pepper
Black pepper is a flowering vine in the family Piperaceae, cultivated for its fruit, which is usually dried and used as a spice and seasoning. The fruit, known as a peppercorn when dried, is approximately in diameter, dark red when fully mature, and, like all drupes, contains a single seed...
gives the family its common name of pepperwort.
Sorus
A sorus is a cluster of sporangia .In fungi and lichens, the sorus is surrounded by an external layer. In some red algae it may take the form of a depression into the thallus....
, each of which consists of several sporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
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 megasporangia, each of which will produce a single large female megaspore
Megaspore
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These types of plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gametophyte, which is fertilized by sperm produced...
. Surrounding them at the edge of the sorus and developing later are the microsporangia, each of which will produce many small male microspore
Microspore
In biology, a microspore is a small spore as contrasted to the larger megaspore.In botany, microspores develop into male gametophytes, whereas megaspores develop into female gametophytes. The combination of megaspores and microspores is found only in heterosporous organisms...
s.
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
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s and conifers, 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 hydrated
Tissue hydration
Tissue hydration is the process of absorbing and retaining water in biological tissues.-Plants:Land plants maintain adequate tissue hydration by means of an outer waterproof layer. In soft or green tissues, this is usually a waxy cuticle over the outer epidermis...
. 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.
Human uses
Some species of Marsilea are cultivated in gardenGarden
A garden is a planned space, usually outdoors, set aside for the display, cultivation, and enjoyment of plants and other forms of nature. The garden can incorporate both natural and man-made materials. The most common form today is known as a residential garden, but the term garden has...
pools or aquaria
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
. The Indigenous Australians
Indigenous Australians
Indigenous Australians are the original inhabitants of the Australian continent and nearby islands. The Aboriginal Indigenous Australians migrated from the Indian continent around 75,000 to 100,000 years ago....
once made a porridge
Porridge
Porridge is a dish made by boiling oats or other cereal meals in water, milk, or both. It is usually served hot in a bowl or dish...
of pulverized Marsilea sporocarps called nardoo
Marsilea
Marsilea is a genus of approximately 65 species of aquatic ferns of the family Marsileaceae.These small plants are of unusual appearance and do not resemble common ferns...
. However, the sporocarps contain toxic levels of thiaminase
Thiaminase
Thiaminase is an enzyme that metabolizes or breaks down thiamine into two molecular parts.The old name was "Aneurinase".There are two types: -Sources:Source include:* Bracken , Nardoo and other plants.* Some fish including carp and goldfish....
, so careful preparation methods must be used in order for the nardoo to be safe for consumption.