Pteridophyta Ferns

Pteridophytes are vascular cryptogams propagated partly vegetatively and partly by spores which are dispersed by wind or water. The technique of propagation by spores is lengthy and requires considerable knowledge. For this reason aquatic ferns are generally propagated vegetatively either by dividing the rhizomes and stems or by separating new plantlets developing directly on the leaves of parent plants.

ISOETACEAE (Quillwort Family)

This family contains two genera and is represented by perennial plants living either submersed or amphibiously (the latter is especially the case with the species from the Mediterranean area). There are also species with land forms that live on wet soils. The subterranean rhizome is generally short, the narrow leaves forming a dense rosette. The lower surface of the leaf is usually ovate and the upper surface is awl-shaped, Roots are fibrillar and branched.

ISOETES on. ioe)

The genus Isoetes has about 75 species distributed in the warm areas of the northern hemisphere. Only a small number of species are found in the southern temperate zone or in the tropics. Water birds and rodents like to eat the stems of Isoetes.

Sterile plants can be determined only with difficulty. Some plants of this genus are imported occasionally for aquariums, but identification is difficult or impossible. Most often they belong to

I. lacustris is found in Europe, Siberia, and North America. The rhizome is 20 to 30 mm long, globular; leaves are dark green, stiff, cylindrical in cross section, 8 to 28 cm long, and 8 to 30 mm

It grows in clear water with a sandy substrate, mainly in lakes (rarely in ponds) at a depth of 30 cm to 3 meters. When the water is silted or frequently disturbed, it disappears quickly.

In spite of growing in cold lakes in nature, I. lacustris does well in temperatures above 68c F (20° C). It requires soft water and some shade. The plant is propagated by dividing older tufts or


This slow-growing species from Europe differs from I. lacustris by its thicker rhizome (10 cm long) and fine, short-pointed leaves. Both species grow under the same conditions in nature. It requires very cool water and soon dies in aquariums.

ISOETES MALINVERNIANA Cesti et de Notaris (in, 10s)

The habitat of this species is the Po River basin in Italy, where it grows in local brooks. It is the largest of European species, has light green leaves 30 cm to 1 meter long and 1 to 2.2 mm thick.

This is a well known species in the aquarium, requiring water with temperatures from 68° to 77° F (20° to 25° C) and reasonably deep tanks where its size can be best displayed. It can be propagated not only vegetatively but also by spores sown in the sand where, with sufficient heat and moisture, they germinate readily. When the plants are about 10 mm high they are transplanted and set out at intervals of about 30 mm. Before reaching 'a height of about 10 cm they are replanted several times; later they can be transplanted'into a tank. Great care and attention should be given during transplantation as the plants are very fragile.

The family consists of minute aquatic ferns floating on the surface or growing in a moist medium as terrestrial forms. The plants have a very short, branching stem. Azolla, with six species distributed from the tropics to the temperate zone of both hemis-

Marsilea quadrifolia. cultivated emersed.

Marsilea quadrifolia. cultivated emersed.

Cryptocoryne pan/a from Ceylon with inflorescence. Phofo by T.J Horeman.

Cryptocoryne pan/a from Ceylon with inflorescence. Phofo by T.J Horeman.

Close-up photograph of the inflorescence of Cryptocoryne parva. Photo by T.J, Horeman.
A small group of floating Azolla filicutotdes. Photo by Dr. D. Sculthorpe

These are not desirable plants in aquariums because they can grow too profusely, like a weed. Under different situations in nature Azolla is regarded to be an undesirable weed or a very beneficial plant. The Azolla - blue-green alga combination fixes atmospheric nitrogen and is widely used as fertilizer and as forage. Azolla is best suited for terrariums and paludariums; it can provide small shallow pools with a decorative growth or cover the surface of moist sand with a varied red-green mosaic carpet. The following species of Azolla (water-velvet) are cultivated.


This species is distributed throughout North and South America and the West Indies. It was introduced to Europe and is now found in many places (Germany, Netherlands, Czechoslovakia), often only temporarily, The plants hardly reach a length of 5 to 12 mm and are round in outline. The stem as well as the leaves are often intensely reddish or green with red margins.


This plant, a native of South America, was brought to Europe and now grows in the same areas as the preceding species plus France and Italy, Compared to A. caroliniana, the plants are larger (10 to 25 mm). Both species float on the water with the greater part of the plant being above the surface, so with intensive vegetative propagation it does not take long to cover the surface of the aquarium.

SALVINIACEAE (Salvinia Family)

The Salviniaceae is represented by annual to perennial rootless plants floating on the surface of the water. The leaves grow on short stalks; two leaves are green and very hairy, while the third is finely divided and submersed, acting as a root. Salvinia is the only genus of the family. It includes 12 species which are found mostly in the tropics of America and Africa (S. natans reaches the temperate zone). Due to introduction the family is almost cosmopolitan. Salvinia has become a very serious pest in southeastern Africa, Ceylon, and southern India.

These are suitable plants for shading the surface of the water. Propagation is fast. The majority of Salvinia species (floating moss), especially those that have well developed root hairs, form a favorable medium for the spawning of fish.

SALVINIA AURICULATA Aublet (m. -ice, im)

This species comes from tropical America. It differs from S. natans in having round to ovate leaves. In the aquarium it requires water with temperatures from 66° to 77° F (18° to 25° C) and a bright situation. As in the majority of floating plants, it is recommended that the aquarium be covered with a sheet of glass to retain the humid conditions.

S. natans is found in the warmer areas of Europe and in eastern Asia. The leaves are elliptical to ovate and 5 to 15 mm long, their surface covered with short, stiff cilia (hair-like processes).

In nature this species grows in quiet backwaters, pools, and canals with slow moving water where during the summer it often forms a very dense growth on the surface of the water, dying off in autumn. In the aquarium it requires a great deal of light; in rooms heated by gas it becomes pale green and often does not last long. Propagation is by runners.


S. rotundifolia comes from South and Central America. The leaves are round, 10 mm long, and densely covered with cilia. It grows in pools and ponds and requires warmer water.


This species is probably the most convenient for aquariums. It grows well at temperatures from 20° to 32° C, winters well, and endures oscillation of the pH, Although it comes from South America (from Santa Catarina, southern Brazil), it can bp used together with cryptocorynes. Its rounded, nearly sessile leaves are only 6 to 9 mm long. Submersed leaves are divided into 5 to 6 segments {each 25 to 76 mm long) and look like roots. In the water they form a thick network of greyish white or pinkish "rootlets" in which young viviparous fish like to live. Islets of floating plants serve as spawning plants to many species of fish and are used for building bubblenests by fightingfish and gouramis.

MAKSILEACEAE (Marsilea Family) This family is comprised of amphibious ferns that are rooted on the bottom with submersed, floating, and aerial leaves as well. Some species develop terrestrial forms. This family of perennial plants includes three genera: Marsilea (about 65 species), Pilularia (6 species), and Regnellidium (1 species). They have a creeping rhizome with developed roots at the base. The leaves are of various shapes and arranged mostly in two rows on the rhizome; young leaves are rolled. The plants live mainly in a marshy environment and are propagated by division of the rhizome.


The leaf stalk is long, terminating in four leaflets which are arranged symmetrically cross-wise; the plant is submersed, floating, or emersed. Its distribution ranges from the tropics to the warmer areas of the temperate zone of both hemispheres. Only two species are fit for the aquarium: the European M, quadrifolia and the Australian M. browni. All the other species are suitable only for paludariums and terrariums, as they do not grow under water. In nature Marsilea is found in ponds, ditches, swamps, rice paddies, and other areas with standing water. Several species are regarded as troublesome weeds in rice fields and irrigation ditches.


This species comes from Australia, growing there in marshes as an amphibious plant. The smallest of the imported species, in its terrestrial form it has petioles that are not more than 80 mm long. The leaves are smaller than in the other species. Juvenile foliage is glossy, but later develops a soft downy or ciliate covering. This species forms sporocarps more readily than others. Under water only simple to 2-parted leaflets are formed on the petioles. The plants reach a maximum height of 25 to 50 mm.

This plant propagates as speedily in deep water as in a marshy habitat, the thin rhizomes taking root quickly, During summer a dense green or olive carpet is formed on the bottom. It is best cultivated in soft, moderately acid or neutral water and is the most suitable species for aquariums and terrariums. It hibernates in all forms.


AÍ. quadrifolia is found in central and southern Europe, Caucasia, western Siberia, Afghanistan, southwestern India, China, Japan, and North America, It has a long creeping rhizome from which leaves similar to a four-leaf clover develop in two rows.

In the aquarium this species should be cultivated in sand and in the shade. Only in this way will it prosper under water, the petioles growing to a length of 10 to 15 cm. In bright situations the petioles become elongated and the leaves reach the surface and emerge from the water. It is less suitable for paludariums and terrariums as in these situations the plant develops petioles that are up to 20 cm long and become prostrate.


This genus contains minute plants with narrow cylindrical leaves; the juvenile foliage is coiled as in other ferns. They are generally found on the banks of shallow waters. Only P. globulifera is cultivated.

The rhizome is 20 to 50 cm long (in submersed forms it can grow to 2 meters), creeping, pilose or bare, and densely covered with cylindrical leaves which are 2.5 to 10 cm long in land forms and 30 cm long in submersed forms.

It grows in shallow water in pools and ponds, most frequently on substrates ranging from sand to fine silt. The plant is sensitive to alkaline conditions and prefers cool waters but temporarily withstands higher temperatures. Under water it usually dies at the approach of winter, a disadvantage which makes it more suitable for terrariums, where it can form an attractive carpet,

Except for having only two leaflets this genus is like Marsilea.

Ceratopteris pteroides Is an appropriate plant for spawning fish. Newly hatched fry can seek protection in Its fine root system.

The unique fi. diphyllum Lindm, is endemic to southern Brazil and northern Argentina. Although regarded as an aquarium plant, this species does not grow under water permanently and is suitable only for paludariums.

CERATOPTERIDACEAE (Parkeriaceae) {Ceratopteris Family)

This family (with the single genus Ceratopteris) consists of annual floating or rooted ferns living in water or marshes. The leaves are of various shapes and sporangia are formed on their lower surface. Ceratopteris (6 species) grows in the tropics and subtropics and is mainly confined to shallow waters. The plants are propagated partly by axillary buds on the leaf margins and partly (during maturity) by generative reproduction from spores which germinate readily. Propagation in the aquarium is similar to that of Isoetes. <111. ei)

Ceratopteris thalicroides

All cultivated species are usually regarded in existing aquarium literature as forms or varieties of a single species, C. thalicroides. Plants with wide leaf blades are labeled as C. thalicroides, plants with deeply indented leaves as C. thalicroides var. javatii-cus, and floating plants as C, thalicroides form cornuta. The identity of floating plants of C. cornuta (P. Beauv.) Lepr. coming from Africa is doubtful. They often represent the following three species:

CERATOPTERIS PTEROIDES (Hooker) Hieron <111.122)

C. pteroides extends to tropical Asia and America. Rosettes of four to six leaves are formed. The petioles are flat, green, 25 to 75 mm long, and widen into lance-shaped or heart-shaped blades. The leaves are sometimes nearly entire, but their sides are usually incised and resemble oak leaves. On the margins or on the ribs new plantlets arise that separate (in this way become islets). The widely branched roots form an ideal hiding place for viviparous fish. At the same time they serve as a suitable spawning medium for-many species of aquarium fish. Gouramis like to build their bubblenests

C. pteroides is grown on the surface of water that is acid and soft and has a minimum temperature of about 18° C, although it grows best with 25° to 30° C. Sometimes it propagates too rapidly, but the number of plants can be reduced. This plant dislikes hard and alkaline water but does not mind plenty of light or half-shade.


The leaves (50 to 80 cm long) have petioles that are three to seven times shorter than the blade, which is green, flat, and very fragile. The blades are deeply incised, but the indentation does not reach as far into the petiole, so the rib is 12 to 25 mm wide. The blades are typically odd-pinnate and the leaf segments are 25 to 75 mm wide. In older literature it is characterized as a broadleaved

This species prefers acid waters (pH 5-6.5) and deeply shaded places. Its bright green color and incised leaves serve as a most suitable complement to cryptocorynes. Having a rather poor root system, it gets nutriment mainly from the water. It is an annual plant. To keep it alive during winter the light has to be prolonged to 12 hours a day or it will die. Some of the youngest spirally twisted leaves can be saved and will develop in the spring. Ceratopteris is tasty food for aquarium snails. During the period of retarded growth (especially in winter), the number of snails has to be reduced; only smaller individuals up to 12 mm can be kept.


Incorrect name: C. thalicroides var. javanicus

The leaves are 25 to 113 cm long, with petioles narrower than in the preceding species; deep incisions reach to the petioles so they are typically odd-pinnate. The individual segments of the leaves grow on the petioles in pairs standing against each other as well— thus a double odd-pinnate leaf. The leaves are much more ragged, the individual segments only 2.5 to 7.5 mm. It is cultivated in the same conditions as C. thalicroides, but is more decorative and grows easily. It is amphibious and often forms emersed leaves, so it can be grown as a terrestrial form in paludariums, where it reproduces quite easily also.

Ceratopteris siliquosa

Ceratopteris siliquosa

Microsorium pteropus (broad-leaved plant in background). Photo by Dr. D Terver.
Microsorium p tempos

POLYPODIACEAE (Polypody Family)

The Polypodiaceae is the largest family of ferns and contains perennial plants with a prostrate rhizome. Juvenile foliage is spirally coiled. The blades are copiously divided or only lobate, rarely smooth-edged. Many species grow on moist, periodically flooded soil. Only two species are cultivated in aquariums.


M. pteropus comes from India, southern China, and the Indo-Malayan area as far as the Philippine Islands, where it is found as an amphibious plant attached to old tree trunks, stones, or the ground.

The plant has a creeping rhizome from which dark brown plume-like petioles develop with leaf blades that are 10 to 25 cm long and 25 to 75 mm wide. The blades are wide, lanceolate, smooth-edged, and green to brownish green with a distinct nervation; leaf margins are undulate.

This is one of the most beautiful aquarium plants. It is not exacting with respect to the composition of the water and grows well in a good light as well as in more shaded positions. Reproduction is by the separation of daughter plants which arise on the leaf margins of fully developed specimens and take root readily.

To cultivate this fern it is necessary to attach it to submersed branches or fasten it to the rocks used as decorations in the tank. After some time the roots become firmly attached. It should never be planted in sand. M. pteropus requires temperatures of about 68° to 77° F (20° to 25° C). Very suitable for paludariums, it grows over rocks, stumps, or branches but requires artificial illumination.

BOLBITIS HEUDELOTH (Rory ex Fee) Alston (in. 121)

The interesting water fern B, heudelotii comes from Guinea in tropical Africa. Its leaves are 25 to 37.5 cm long, odd-pinnate, with five to seven incisions on both sides of the blades, which are dark olive green, bottle green, or brownish. Cultivation is slightly more difficult than with the preceding species. Bolbitis is not planted in the bottom, but the plants can be fastened to stones or roots used as decorations in the aquarium. It demands a clear, soft to medium hard water and temperatures from 72° to 82° F (22° to 28° C). It does not do well in thickly planted tanks. This plant likes moving water and grows well when placed next to the filtering system, which enhances their normally slow growth. Sometimes algae can stop the development and growth of these plants, nor should there be too many fish in the tank. Successful aquarists often cultivate this species on decorative roots together with fish of the genus Aphyosemion.

Other species like Bolbitis jhwiatilis (Hook.) Ching from tropical West Africa, B. hydrophylla (Copel) from the Philippines, andB. lonchospora (Ktze.) C. Chr. from Polynesia should also be considered for the aquarium. Even their names (fluviatilis, hydrophylla) indicate that they are water ferns.

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