Characteristic features and life cycle patterns of Pteridophytes
Discipline: Botany Paper: Pteridophytes Lesson: Characteristic Features and Life Cycle patterns of Pteridophytes Lesson Developer: Dr.P.L.Uniyal, Dr. Ruchi Srivastava Department/College: Department of Botany, University of Delhi
Lesson Reviewer: Dr Satish Agarwal Department/College:Deshbandhu College
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL
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Characteristic features and life cycle patterns of Pteridophytes
Table of Contents
Introduction
History
Classification
Ferns and Fern – allies
Cooksonia
Psilophyta
1.Class Psilotophytopsida
2. Class Psilotopsida
Lycophyta
Sphenophyta
Pterophyta
Parts of a Pteridophytic Plants
Parts of a fern fronds
Root, Stem, Leaves and Sporangia
Sorus
Simple sorus
Gradate sorus
Mixed sorus
Sporocarp
Sex organs
Antheridia
Archegonia
Sporophyte
Life cycle of a homosporous fern
Summary
Exercises
References/Bibliography/Further Reading Institute of Lifelong Learning, University of Delhi
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Characteristic features and life cycle patterns of Pteridophytes
Introduction Pteridophytes are the primitive land vascular cryptogamic (seedless) plants. The term Cryptogam is derived from two Greek word i.e. Cryptos means hidden and Gamos means marriage i.e. hidden marriage. Cryptogams include all those plants which reproduce by means of spores and never produce seeds. Cryptogams include Algae, Fungi, Bryophytes and
Pteridophytes.
Cryptogams appeared in the Silurian period of the Paleozoic era (425 million years ago) and constituted dominant vegetation on the earth during Devonian period (360 million years ago) (Fig.1, 2).
Fig.1 Pictorial depiction of vegetation during carboniferous period Source:http://trivialist10.wordpress.com/2012/05/29/mass-extinctions/
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Characteristic features and life cycle patterns of Pteridophytes Fig.2. Pictorial depiction of fauna and flora during carboniferous period Source:http://en.wikipedia.org/wiki/Jurassic
Classification According to Ostwald Tippo (1942) divided plant kingdom into two subkingdom; Thallophyta and Embryophyta and the later divided into Bryophyta and Tracheophyta. Pteridophytes are included in subphyla Pteridophyta (Fig.3).
KINGDOM : PLANTAE
I. SUB-KINGDOM : THALLOPHYTA (Plants without embryo)
II. SUB-KINGDOM : EMBRYOPHYTA (Plants with embryo)
1.PHYLA: Cyanophyta 2.PHYLA: Euglenophyta
1.PHYLA: Bryophyta
2.PHYLA: Tracheophyta (Vascular plants)
1.CLASS: Musci (Mosses)
3.PHYLA: Chlorophyta
2.CLASS: Hepaticeae (Liverworts) 4.PHYLA: Chrysophyta 3.CLASS: Anthocerotae (Hornworts)
5.PHYLA: Pyrrophyta 6.PHYLA: Phaeophyta 7.PHYLA: Rhodophyta
1.SUBPHYLA: Psilopsida
2.SUBPHYLA: Lycopsida (Club mosses)
8.PHYLA: Schizomycophyta
3.SUBPHYLA: Sphenopsida (Horsetails)
4.SUBPHYLA: Pteropsida
9.PHYLA: Myxomycophyta 10.PHYLA: Eumycophyta
1.Class: Filicinae (Ferns)
1.SUBCLASS:Cycadophytae
2.Class: Gymnospermae
3.Class: Angiospermae
2.SUBCLASS:Coniferophytae
1.SUBCLASS:Dicotyledonae
2.SUBCLASS:Monocotyledonae
Fig.3. Classification by Ostwald Tippo (1942)
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Characteristic features and life cycle patterns of Pteridophytes On the basis of morphology, structure and details of the reproduction Pteridophytes are divided into four classes: Division - Pteridophyta Ferns
Fern - allies
Class- Filicopsida/Filicales (True Ferns)
Class-Psilotopsida
Class-Lycopsida
Class - Equisetopsida
A classification for extant ferns By Smith et al (2006) In this new classification 4 monophyletic classes, 11monophyletic orders, and 37 families, 32 of which are strongly supported as monophyletic. One new family, Cibotiaceae Korall, is described. The phylogenetic affinities of a few genera in the order Polypodiales are unclear and their familial placements are therefore tentative. Alphabetical lists of accepted genera (including common synonyms), families, orders, and taxa of higher rank are provided (Fig.4). Within ferns, 4 classes; 1. PSILOTOPSIDA A. ORDER OPHIOGLOSSALES. 1. Family Ophioglossaceae. — Ophioglossoids; incl. Botrychiaceae, Helminthostachyaceae. Four genera: Botrychium (grapeferns; moonworts), Helminthostachys, Mankyua1, Ophioglossum (adder tongues). B. ORDER PSILOTALES. 2. Family Psilotaceae. — Whisk ferns; incl. Tmesipteridaceae. Two genera : (Psilotum, Tmesipteris), ca. 12 total spp. (2 in Psilotum) 2. Equisetopsida [= SPHENOPSIDA]. C. ORDER EQUISETALES. 3. Family Equisetaceae.Horsetails. A single genus (Equisetum), 15 spp. 3. Marattiopsida
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Characteristic features and life cycle patterns of Pteridophytes D. ORDER MARATTIALES. — Including Christenseniales. 4. Family Marattiaceae. — Marattioids; incl. Angiopteridaceae, Christenseniaceae, Danaeaceae, Kaulfussiaceae. Four genera: Angiopteris, Christensenia, Danaea, Marattia 4. Polypodiopsida [= FILICOPSIDA] E. ORDER OSMUNDALES. 5. Family Osmundaceae. — Three genera: Leptopteris,Osmunda, Todea. Ca. 20 spp.; F. ORDER HYMENOPHYLLALES. 6. Family Hymenophyllaceae. — Filmy ferns; incl. Trichomanaceae. Nine genera, two major clades “trichomanoid”and “hymenophylloid”, roughly corresponding to the classical genera Trichomanes and Hymenophyllums Ca. 600 spp. G. ORDER GLEICHENIALES. — Including Dipteridales, Matoniales, Stromatopteridales. 7. Family Gleicheniaceae. — Gleichenioids, forking ferns; incl. Dicranopteridaceae, Stromatopteridaceae. Six genera (Dicranopteris, Diplopterygium,Gleichenella, Gleichenia, Sticherus, Stromatopteris),ca. 125 spp. 8. Family Dipteridaceae. — Including Cheiropleuriaceae.Two genera, Cheiropleuria and Dipteris, 9. Family Matoniaceae. — Matonioids. Two genera (Matonia, Phanerosorus), each with two spp.; H. ORDER SCHIZAEALES. 10. Family Lygodiaceae. — Climbing ferns. A single genus (Lygodium), ca. 25 spp. 11. Family Anemiaceae. — Including Mohriaceae. One genus (Anemia, incl. Mohria), ca. 100+ spp. 12. Family Schizaeaceae. — Two genera (Actinostachys,Schizaea), ca. 30 spp. I. ORDER SALVINIALES. — Water ferns, heterosporous ferns; incl. “Hydropteridales”, Marsileales, Pilulariales 13. Family Marsileaceae. — Clover ferns, incl. Pilulariaceae. Three genera (Marsilea, Pilularia, Regnellidium), ca. 75 total spp.
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Characteristic features and life cycle patterns of Pteridophytes 14. Family Salviniaceae. — Floating ferns, mosquito ferns; incl. Azollaceae. Two genera (Salvinia, Azolla), ca. 16 spp. J. ORDER CYATHEALES. — Tree ferns; incl. Dicksoniales, Hymenophyllopsidales, Loxomatales, Metaxyales, Plagiogyriales 15. Family Thyrsopteridaceae. — One genus, Thyrsopteris, with a single species, T. elegans 16. Family Loxomataceae. — Two genera (Loxoma,Loxsomopsis), each with a single sp. 17. Family Culcitaceae. — One genus, Culcita,with two species; 18. Family Plagiogyriaceae. — A single genus (Plagiogyria), with ca. 15 spp. 19. Family Cibotiaceae Korall, with subfam. Cibotioideae One genus (Cibotium), ca. 11 species 20. Family Cyatheaceae. — Cyatheoids, scaly tree ferns; incl. Alsophilaceae, Hymenophyllopsidaceae. Ca. five genera: Alsophila (incl. Nephelea), Cyathea (incl.Cnemidaria, Hemitelia, Trichipteris), Gymnosphaera, Hymenophyllopsis, Sphaeropteris (incl. Fourniera);600+ spp. 21. Family Dicksoniaceae, nom. cons. —(Dicksonioids; incl. Lophosoriaceae). Three genera: Calochlaena, Dicksonia, Lophosoria). Ca. 30 spp. 22. Family Metaxyaceae. — Asingle genus (Metaxya),2 spp. K. ORDER POLYPODIALES. — Including “Aspidiales”,Aspleniales, Athyriales, Blechnales, “Davalliales”, Dennstaedtiales, Dryopteridales, Lindsaeales, Lonchitidales,Monachosorales, Negripteridales, Parkeriales, Platyzomatales, Pteridales, Saccolomatales, Thelypteridales. 23. Family Lindsaeaceae. — Lindsaeoids; incl.Cystodiaceae, Lonchitidaceae. Ca. eight genera: Cystodium, Lindsaea, Lonchitis, Odontosoria, Ormoloma1, Sphenomeris,Tapeinidium, Xyropteris1 24. Family Saccolomataceae. — One genus, ca.12 spp. 25. Family Dennstaedtiaceae. — Dennstaedtioids;incl. Hypolepidaceae, Monachosoraceae, Pteridiaceae. Ca. 11 genera: Blotiella, Coptodipteris, Dennstaedtia (incl. Costaricia1), Histiopteris, Hypolepis,Leptolepia, Microlepia, Monachosorum, Oenotrichia s.s.1, Paesia, Pteridium (bracken). Ca. 170 spp.;
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Characteristic features and life cycle patterns of Pteridophytes 26. Family Pteridaceae. — Pteroids or pteridoids; incl. Acrostichaceae, Actiniopteridaceae, Adiantaceae (adiantoids, maidenhairs), Anopteraceae, Antrophyaceae, Ceratopteridaceae, Cheilanthaceae (cheilanthoids), Cryptogrammaceae, Hemionitidaceae, Negripteridaceae,Parkeriaceae, Platyzomataceae, Sinopteridaceae, Taenitidaceae (taenitidoids), Vittariaceae (vittarioids, shoestring ferns). Ca. 50 genera, 950 spp. 27. Family Aspleniaceae. — Asplenioids, spleenworts. From one to ten genera, a huge majority of the species are in Asplenium 28. Family Thelypteridaceae. — Thelypteroids or thelypteridoids; incl. “Sphaerostephanaceae” 29. Family Woodsiaceae. — Athyrioids, lady ferns; incl. Athyriaceae, Cystopteridaceae. Circa 15 genera as defined here, ca. 700 spp., 30. Family Blechnaceae. — Blechnoids; incl. Stenochlaenaceae). Currently ca. nine genera recognized (Blechnum s.l., Brainea, Doodia, Pteridoblechnum, Sadleria,Salpichlaena, Steenisioblechnum, Stenochlaena, Woodwardia). Most of the existing recognized genera nest within Blechnum s.l., and their acceptance is dependent upon a revised recircumscription of Blechnum s.l., Ca. 200 spp.; monophyletic, 31. Family Onocleaceae. — Onocleoids. Four genera: Matteuccia, Onoclea, Onocleopsis, Pentarhizidium. 5 spp. 32. Family Dryopteridaceae. — Dryopteroids or dryopteridoids; incl. “Aspidiaceae”, Bolbitidaceae, Elaphoglossaceae, Hypodematiaceae, Peranemataceae. 40–45 genera, 1700 spp., 33. Family Lomariopsidaceae. — Lomariopsids; incl. Nephrolepidaceae, sword ferns. Four genera: Cyclopeltis, Lomariopsis, Nephrolepis, and Thysanosoria1; ca. 70 species. 34. Family Tectariaceae. — Tectarioids; incl. “Dictyoxiphiaceae”, “Hypoderriaceae”. 8–15 genera: Aenigmopteris1, Arthropteris, Heterogonium, Hypoderris1,Pleocnemia, Psammiosorus, Psomiocarpa1, Pteridrys,Tectaria s.l. (incl. Amphiblestra1, Camptodium1,Chlamydogramme1, Cionidium, Ctenitopsis, Dictyoxiphium,Fadyenia, Hemigramma, Pleuroderris1, Pseudotectaria1,Quercifilix, Triplophyllum 230 species
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Characteristic features and life cycle patterns of Pteridophytes 35. Family Oleandraceae. — Monogeneric, ca.40 spp. included two genera in addition to Oleandra: Arthropteris (ca. 12 spp.), and Psammiosorus 36. Family Davalliaceae. — Davallioids; excl. Gymnogrammitidaceae. 4–5 genera: Araiostegia, Davallia (incl. Humata, Parasorus, Scyphularia), Davallodes,Pachypleuria; ca. 65 spp. 37. Family Polypodiaceae. — Polygrams; incl. Drynariaceae, Grammitidaceae (grammitids), Gymnogrammitidaceae, Loxogrammaceae, Platyceriaceae, Pleurisoriopsidaceae. Ca. 56 genera, ca. 1200 spp. 11 orders, and 37 families.
Fig.4. Modern classification of extant fern by Smith et al.
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Characteristic features and life cycle patterns of Pteridophytes Ferns and Fern - allies Pteridophytes consist of two important groups; Ferns and Fern-allies. The easiest way to differentiate between these two groups is as follows; S.No.
Ferns
Fern - allies
1
Fern have large leaves which is known as
Fern – allies have small
Fronds
scale like leaves known as microphylls
2 3
4
Young leaf is coiled just like the spring of a
Circinate vernation is not
clock and it is called as circinate vernation.
found
Sporangia are produced on the lower surface of
Sporangia are produced in
the leaf
the axils of sporophylls
Sporangia remain aggregated in the sori
Sporangia
are
individually
or
found in
the
specialized cone called as strobili Pteridophytes are considered under vascular cryptogams as they have well developed vascular system. Other cryptogams i.e. Algae, Fungi and Bryophytes don’t have lignified vascular system. Pteridophyte mainly includes Lycopodes and ferns. The earliest vascular plant Cooksonia is known ranging from upper Silurian to lower Devonian in north and South America and Europe. Cooksonia were dichotomously branched short with terminal sporangia (Fig.5).
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Characteristic features and life cycle patterns of Pteridophytes
Fig.5 Cooksonia: Diagrammatic sketch of the thallus Source:http://www.carlwozniak.com/earth/silurian/sil03b.html
Only the sporophytic phase of Cooksonia is currently known (i.e. the phase which produces spores not the gametes). The plants were very few centimeter tall and simple structure and lacking leaves, roots, flowers etc. The plants bears simple stalk which branched dichotomously and each branches terminated in a spore bearing structure called sporangium. The centres of their stalk have a dark stripe which has been assumed as the remains of water carrying tissue. Some species of Cooksonia contained stomata which probably functions in transpiration. Division Psilophyta This division has both living as well as extinct plants. Vascular system is of very simple type. It is divided in two classes; 1.Class Psilotophytopsida This class has all the extinct members which are known by Aglaophyton, Horneophyton, Cooksonia etc. Only sporophyte is known of this class. The main characteristic of this class are;
Plant body is divided into undergorund rhizome and aerial nacked branches.
In place of roots, unicellular rhizoids are found in tufts on the rhizome.
Sporangia are terminal or lateral in position homosporous and in the vascular system, the central solid core of xylem tissue is surrounded by phloem (protostelic).
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Characteristic features and life cycle patterns of Pteridophytes 2. Class Psilotopsida This class is represented by two genera i.e., Psilotum, Tmesipteris. The main characteristic of this class are;
The plant body is sporophyte and divided into two parts; underground rhizome and aerial dichotomous branches. Rhizome has mycorrhizal association of fungal hyphae.
Aerial branch contains some leaf like appandages.
Stele is protostele.
They are homosporus.
Multiflagellated antherozoids are found.
Lycophyta This division has both living as well as fossil members. It includes five living members i.e., Lycopodium, Phylloglossum, Selaginella, Stylites and Isoetes. The main characteristic of this division are;
Sporophytic plant consists of roots, stems and small microphyllous leaves.
The plants may be homosporous or heterosporous.
Antherozoids are biflagellate or multiflagellate.
Sphenophyta This division has only one representative i.e. Equisetum. The main characteristic of this division are;
Sporophyte is differentiated into roots, stem and leaves.
Stem is jointed, solid and protostelic. Some members show secondary growth.
Sporangia are found in terminal cone / strobilus.
Antherozoids are multiflagellate.
Spores contain elators.
The anatomy of the stem of Equisetum is showing a combination of hydrophytic and xerophytic characters.
The nodes and internodes have different internal structures. In transverse section, internode differentiated into epidermis, cortex, endodermis, pericycle and vascular cylinder.
Epidermis is encrusted with heavy deposition of silica.
Cortex is differentiated into outer sclerenchymatous and chlorenchymatous and inner paranchymatous region having large schizolysogenous canals called as vallecular canals.
Cortex is followed by single-layered endodermis.
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Characteristic features and life cycle patterns of Pteridophytes
The endodermis is delimited from stele by single-layered paranchymatous pericycle. The vascular cylinder is siphanostele having a large conspicuous protoxylem lacuna called carinal canal.
The central part of aerial shoot is occupied by a large pith.
The internal structure of node has a central solid diaphragm instead of hollow cavity. Vallecular as well as carinal canals are absent in the nodal region.
The transverse section of rhizome is differentiated into epidermis, cortex, endodermis, pericycle and vascular bundles like that of the stem, but it differs from stem in the absence of stomata in epidermis and cortex is without chlorenchymatous cells.
The roots show epiblema, cortex and stele.
A characteristic feature of the root of Equisetum is the presence of two layered endodermis.
The xylem is diarch to tetrarch.
The plant reproduces both vegetatively as well as asexually.
The vegetative reproduction takes place by tubers.
Asexual
reproduction
occurs
by
spores
developed
within
sporangia
borne
on
sporangiophores.
Since Equisetum is a homosporous pteridophyte, spores formed are all alike.
These spores germinate to form prothallus, which bears male and female sex organs and reproduces sexually to form an embryo, regenerating the sporophyte plant, the dominant phase of the life cycle.
Pterophyta This division comprises a large number of genera and species. The plants have large megaphyllous leaves in comparison to other. The main characteristic of this division are;
Sporophytes are differentiated into rhizome, roots and leaves
The rhizome may be creeping or erect with aerial stem.
Leaves are dimorphic.
Sporangia are found in the sori.
Stele may be protostele, siphonostele or dictyostele.
Some members of Ophioglossum, Helminthostachys, Nephrolepis, Pteris etc. bears vessels in the xylem.
Parts of a fern plant
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Characteristic features and life cycle patterns of Pteridophytes A fern plant is differentiated into roots, stem (rhizome) and leaves (fronds) (Fig.6). Fern leaves are commonly called as frond. It is generally divided into two parts i.e. stipe and lamina. The basal stalk which supports the blade is called as stipe. The continuation of stipe into blade is called as rachis which is the midrib of a blade. The blade contains leaflets. It may be simple or compound. In compound leaflets the midrib of pinna is called as costa, costules etc. The once divided frond is called as pinnate and further division called as bipinnate, tripinnate etc (Fig.7). In ferns, young leaf is coiled like a spring of a clock which is called the cercinate vernation and this type of leaf is called as crozier (Fig.8, 8a).
Pinna Blade Rachis
Frond (Leaf)
Crozier Rhizome (stem)
Stipe
Roots
Fig.6. Parts of a fern plant
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Characteristic features and life cycle patterns of Pteridophytes
Fig.7 Part of a fern frond Source:https://www.uwgb.edu/biodiversity/herbarium/pteridophytes/pteridophyte_glossary01.ht m
A
B
Fig.8, A-B. Fern crozier. Source:A.http://www.pinterest.com/pin/250653535484045356/, B.Author’s contribution Root, Stem and Leaves There is a typical alternation of generation found in the pteridophytes. The haploid, thalloid gametophytic stage which bears gametangia, alternate with the diploid plant stage, which consists of root, shoots, leaves and sporangia. Institute of Lifelong Learning, University of Delhi
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Characteristic features and life cycle patterns of Pteridophytes
The mature sporophyte is photosynthetic and able to absorb nutrients and water from the substratum. Most of the pteridophytes are terrestrial, grow in moist and shady places. They form luxuriant communities in the high rainfall areas and cool conditions. Many of them grow on the trunck and branches of the trees as epiphytes but they don’t take nutrition from host tree viz., Microsorium, Drynaria etc.(Fig.9c). Some pteridophytes viz., Azolla, Marsilea, Salvinia etc.(Fig.9a) are aquatic and they usually grows in pond water. A few species of Selaginella and Equisetum are xerophytic in nature and can tolerate extreme dessication (Fig.9b). Some Pteridophytes attain a long height of about 20 meters and they are called as Tree fern viz., Cyathea, Alsophila, Dicksonia (Fig.9d).
Fig.9 A.Water fern – Azolla sp.;B. Xerophytic fern – Equisetum sp.;C. Epiphytic fern – Drynaria sp. Source: Author’s contribution Institute of Lifelong Learning, University of Delhi
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Characteristic features and life cycle patterns of Pteridophytes
Fig.9d. Tree fern – Cyathea sp. Source: Author’s contribution The root and stem of Pteridophytes have well developed vascular system which is composed of xylem and Phloem (Fig.10a,b). Xylem consists of long tracheids, parenchyma and fibers but lacks vessels. Phloem comprises sieve cells, parenchyma and fibers and lacks companion cells in majority of pteridophytes. There are some exceptions like Nephrodium filixmas (L.) Schott and Pteridium aquilinum (L.) Kuhn by Russow (1873) where vessels are reported in the xylem.
Cambium is absent in Pteridophytes therefore no secondary growth is found while some pteridophytes like Isoetes, Botrychium show a limited cambial activity and secondary growth.
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Characteristic features and life cycle patterns of Pteridophytes
Fig.10a. T.S. Roots Lycopodium selago A. Aerial roots, B. Cortical roots, C.Diagrammatic T.S. through stem showing one stele and two cortical roots
Fig.10b.Transeverse section of stem of Lycopodium clavatum and Lycopodium cernuum
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Characteristic features and life cycle patterns of Pteridophytes
Fig.10c. V.S. of the leaf of Lycopodium selago The sporangia are produced on the ventral surface of leaves or axil of leaves which are called sporophyll (Fig.11,12).
Fig.11. Sori on ventral surface of leaf-Sporophyll Source:Author’s contribution The development of sporangium may be of Eusporangiate type : when sporangium develops from a group of sporangial initial cells. Eusporangiate development is considered to be primitive found in early pteridophytes (Lycopodiopsida, Sphaenopsida and some ferns). Leptosporangiate type : when development of sporangium occurs from single sporangial initial cell.
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Characteristic features and life cycle patterns of Pteridophytes Sori and sporangia In ferns, Sporangia are aggregated into clustures on the ventral surface of leaf called as sori. However, in some ferns vegetative part of sporophyll is reduced and sporangia appears to be arranged on the mid rib and may form a strobili (eg. Anemia, Ophioglossum etc.). In aquatic ferns sporangia are enclosed in a specialized nut like structure called as sporocarp. In Marsilea, Azolla, Salvinia etc., the sporangia are enclosed in hard covering called sporocarp. The sori are of 3 types;
Fig.12. Enlarge view of sporangia Source: http://www.bio.miami.edu/dana/160/160S12_15print.html (i)
Simple sorus : In this type of sorus sporangia appear, grow and mature at same time e.g. Botrychium,Ophioglossum
(ii) Gradate sorus: In this type central or distal part of the sorus has most mature sporangium and peripheral part has youngest sporangium. They show a gradation of maturity. eg. Marsilea, Cyathea (Fig.13). (iii) Mixed sorus : Mature and immature sporangia remain remain mixed together. eg. Pteridium, Pteris, Adiantum, Polypodium (Singh et al. 2011).
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Characteristic features and life cycle patterns of Pteridophytes
Fig.13. Marsilea quadrifolia. A sporophyte with sporocarps, rhizome, leaves and roots Source:http://www.yourarticlelibrary.com/biology/useful-notes-on-the-life-history-of-marsilea4960-words-2/7081/ Spores develop in the sporangia after the meiosis in the sporogenous tissue. When all the spores in the sporangia of a plant are alike, then they are called as homosporus eg. Pteris, Dryopteris, Microsorium, Polystichum, Lygodium etc. on other hand if spores of sporangia of a plant are of different sizes they are called as heterosporus eg. Selaginella, Marsilea, Pilularia. In the case of hetersporous taxa the large and small spores are called megaspores and microspores respectively the small spores give rise to male prothalli which produce only antheridia and large spores develop into female prothalli which produces only archegonia. However, in homosporous pteridophytes the spores germinate and produce monoecious prothalli which develop antheridia as well as archegonia on the same prothallus. Spores are dispersed from sporangia after dehiscence. The spore is the Ist stage of gametophytic generation. During favourable condition i.e. in less temperature (below 220C) and high humidity, spores germinate and develops into haploid multicellular body generally cordate prothalli (Fig.14).
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Characteristic features and life cycle patterns of Pteridophytes
Fig.14. Developmental stages of a fern plant. A. Spore; B. Rupturing of spore ; C. Filamentous stage D. cordate gametophyte and emerging of rhizoid and protonema Source:Author’s contribution
Gametangia Gametangia are represented by male i.e. antheridia and female i.e. archegonia. Spores from homosporous taxa produces monoecious prothallus in which antheridia and archegonia develops on same prothallus. Some times they are dioecious in nature in heterosporous ferns. Antheridia The antheridia develop in between the rhizoids of prothallus on the ventral surface. The antheridium is a globose structure which has an outer sterile single layered antheridial jacket surrounding inner cellular mass. Antherozoids formed from the inner cellular mass which develops in antheridium. Antherozoids are unicellular, uninucleate and spirally coiled with apically attached two flagella (fig.15a,b). The mature antheridium bursts by rupturing of cap cells in the jacket and antherozoids swim out.
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Characteristic features and life cycle patterns of Pteridophytes
Figure 15: Structure of Antheridia and Antherozoid Source: Author’s contribution; http://chestofbooks.com/gardening- horticulture/plants-andtheir-uses/Part-192-The-Ferns-Plant-Life-Histories-Part-2.html#.U5rLOnKSySo Archegonia
The female sex organs i.e. archegonia develops below the apical notch of prothallus on ventral surface. The archegonium is a flask shaped structure, composed of neck and venter. The neck is made up of 4 vertical rows of neck cells and 2 neck canal cell. Neck canal cell degenerates before fertilization and forms a mucilaginous substance which attracts antherozoids towards archegonium. Venter is the wide base part of archegonium consists of an egg cell and a ventral canal cell (Fig.16).
Archegonia
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Characteristic features and life cycle patterns of Pteridophytes
Fig.16. Structrure of Archegonia Source:Author
Water is essential for swimming of sperm to reach to archegonium. The antherozoids swim in water film and enter into the archegonium via neck and one of them fuses with egg to form diploid zygote. So the fertilization process is facilitates during rainy season with the presence of dew or moist condition. This is the reason that pteridophytes diversity is more in the wet regions.
Fig.17.Young plant of Cheilanthes farinosa-Authors personal contribution Sporophyte Formation of zygote is the beginning of sporophytic generation. The zygote divides to form a well differentiated embryo. The embryo remains embedded in the prothallus and develops into young plant bearing root, shoot and leaves (Fig.17). The roots of young sporophyte soon penetrates into the soil and become an independent plant and the gametophyte (prothallus) degenerates.
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Characteristic features and life cycle patterns of Pteridophytes
Fig.18.Life cycle of a homosporus fern Source:http://www.arctic.uoguelph.ca/cpl/organisms/plants/biology/fernrepro.htm
Summary
The plants of this group are called as vascular cryptogams because they possess the lignified vascular tissue and reproduce by spores instead of seeds. They are the most primitive living and fossil vascular plants.
Pteridophytes grow in a variety of habitats mostly grows well in abundant moisture and shades. A few are aquatic e.g. Marselia, Pilularia, Azolla, Salvinia etc., epiphytic forms e.g. Lycopodium phlegmaria, Asplenium etc are abundant in tropical rain forest.
The plant body is sporophyte and differentiated into root, stem and leaves.
Vascular tissues are present. Xylem is represented by tracheids and lacks vessels. Phloem consists of sieve cells and lacks companion cells. However, in Selaginella, Pteridium, Marselia, Regnellidium and Pilularia vessels have been observed.
Secondary growth does not occur in majority of Pteridophytes.
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Characteristic features and life cycle patterns of Pteridophytes
The sporophytic plant reproduces by means of spores. Isoetes shows some unusal secondary growth. These spores are produced in sporangia through meiotic division, sporangia borne on stems or leaves or in the axil of leaves.
The leaves which bear sporangia are called sporophylls. Sporangia may be clustured to form a cone or strobilus as in Selaginella, Lycopodium etc.
In aquatic ferns e.g. Marselia, Azolla, Salvinia etc. sporangia are produced in a specialized structure called sporocarps
If all the spores produced by a plant by meiosis are alike then the plant is said to be homosporous e.g. Pteris, Dryopteris etc.
If the spores produced are of two different sizes, then the plant will be said to be heterosporus. E.g. Selaginella, Marselia etc. The smaller spores are called as microspores produced in micrsporangia while larger spores are called as megaspores produced in megasporangia.
Spores on germination give rise to small haploid thalloid or filamentous gametophyte called as prothallus.
Gametophyte bears sex organs i.e. antheridia and archegonia.
The gametophyte formed from spore of homosporous plant are monoecious e.g., Pteris, Dryopteris, Lycopodium etc. while in the case of heterosporous plant the small spores form male prothalli which bears only antheridia and large spores form female prothalli which bears only archegonia, thus they are dioecious e.g., Selaginella, Marselia etc.
Sex organs are multicellular and surrounded by sterile jacket. Antherozoids are released from antheridia which need water essentially to travel to archegonia. Fertilization results in formation of zygote.
The zygote develops into a multicellular embryo after a series of mitotic divisions and embryo develops into sporophyte which depends on gametophyte only during its early stage and later on, it becomes an independent plant.
References/Bibliography/Further Reading 1. Singh V, P.C.Pande and D.K.Jain. 2011. A text book of Botany. 4 th edition. Rastogi Publications. Gangotri Shivaji Road, Meerut).
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Characteristic features and life cycle patterns of Pteridophytes 2. Parihar, N.S. 1977. The biology and morphology of the Pteridophytes. Central Book Depot, Allahabad. 3. Raven P.H., R. E. Evert and S.E. Eichhorn, 1999. Biology of Plants. W.H.Freeman and Company Worth Publishers. 4. Vashishta, P.C., Sinha, A.K. and Kumar, A.2010. Pteridophyta. Botany for Degree Students. S.Chand & Company Ltd. 5.
K. R. Sporne. 1962. The Morphology of Pteridophytes. HUTCHINSON & CO. (Publishers) LTD 178-202 Great Portland Street, London.
Exercises 1. Describe the life cycle of a seedless vascular plant. 2. Write a short note on the following (i)
Non-flowering plants
(ii)
Vascular system of a pteridophytic plant
(iii)
Cercinate vernation
(iv)
Homosporus and Heterosporus ferns
(v)
Crozier coiling
3. Draw a labeled diagram of a mature cordate gametophyte Objective Question Question Number
True/False
1. The plant body of pteridophyte is sporophyte.
True or False
2. pteridophytic plants generally grow in moist and
True or False
shady places 3. Water ferns are Selaginella and Equisetum
True or False
4. Xerophytic ferns are Azolla, Marsilea and Salvinia
True or False
5. Vascular system is found in pteridophytes
True or False
6. Xylem is made of vessels and phloem is made of
True or False
companion cells 7. Xylem lacks vessels and phloem lacks companion
True or False
cells in pteridophytes
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Characteristic features and life cycle patterns of Pteridophytes 8. Sporaniga
bearing
leaves
are
known
as
True or False
9. Sori are found on the dorsal surface of the
True or False
sporophylls sporophyll 10. Pilularia is a homosporus fern
True or False
11. First stage of gametophytic generation is spore
True or False
12. Development of antheridia is in between rhizoids
True or False
of gametophyte and development of archegonia is below the apical notch 13. Water is essential for swimming of sperm to reach
True or False
to archegonium. 14. Water is not essential for fertilization
True or False
15. Salvinia is a water fern
True or False
16. Microsorum is an epiphytic fern
True or False
Multiple Choice Questions 1. First land vascular plants are; a) Algae b) Fungi c) Bryophytes d) Pteridophytes 2. Pteridophytes were originated in the; a) Proterozoic era, Devonian period b) Paleozoic era, Silurian period c) Mesozoic era, Triassic Period d) Cenozoic era, 3. Sporophytic body of pteridophytes is; a) ½ n b) n c) 2n d) 4n Institute of Lifelong Learning, University of Delhi
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Characteristic features and life cycle patterns of Pteridophytes
4. Which of the following is a water fern; a) Pteris b) Equisetum c) Marselia d) Osmunda 5. In Pteridophytes, y xylem lacks; a) Tracheids b) Vessels c) Xylem parenchyma d) Xylem fibers
6. In Pteridophytes phloem lacks; a)
Sieve cells
b) Companion cells c)
Phloem fibre
d) Phloem parenchyma 7. Secondary growth is present in; a) Pteris b) Botrychium c) Ophioglossum d) Cyathea 8. Which one is Homosporus fern; a) Marselia b) Pilularia c) Dryopteris d) Lycopodium 9. Which one is Heterosporous fern; a) Selaginella b) Blechnum
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Characteristic features and life cycle patterns of Pteridophytes c) Cyathea d) Asplenium
Fill in the Blanks 1. First land vascular plants are ……………. 2. …………….. generation is the dominant phase of pteridophytes. 3. young leaf is coiled just like the spring of a clock. This is called as …………. Vernation. 4. xylem lacks………. and phloem lacks …………….. in pteridophytes 5. Sporangia bearing leaves are called as ………………. 6. ………. are found in between rhizoids of a cordate gametophyte 7. ……… are present below the apical notch 8. ……………… is essential for fertilization 9. ………….. are unicellular, uninucleate and spirally coiled with two flagella found apically 10. …………… and ………………….. develops on the ventral surface of the gametophyte
Match the Following
1.
First Vascular cryptogamic plants
a) Prothallus
2.
Crozier
b) Frond
3.
Water fern
c) Young coiled leaf
4. Dryopteris cohleata
d) Sporophytic generation
5.
e) Pteridophytes
Flask shaped structure
6. Cordate gametophyte
f)
7. Unicellular and spirally coiled 2 flagellated structure
g) Homosporous ferns
8.
Dominant phase of Pteridophytes
h) Azolla
9.
Spores
i)
Archegonia
j)
Antherozoids
10. Leaf
Haploid phase
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Characteristic features and life cycle patterns of Pteridophytes Answers True/False 1.
True
2.
True
3.
False
4.
False
5.
True
6.
True
7.
True
8.
False
9.
False
10.
True
11.
True
12.
False
13.
True
14.
True
Correct Answers MCQs 1.
d
2.
b
3.
c
4.
c
5.
b
6.
b
7.
b
8.
c
9.
a
Fill in the blanks 1. Pteridophytes 2. Sporophytic 3. Cercinate 4. Vessels, Companion cells Institute of Lifelong Learning, University of Delhi
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Characteristic features and life cycle patterns of Pteridophytes 5. Sporophylls 6. Antheridia 7. Archegonia 8. Water 9. Antherozoids 10.Antheridia and Archegonia Match the following 1. First Vascular cryptogamic plants 2. Crozier
e) Pteridophytes
c) Young coiled leaf
3. Water fern
h) Azolla
4. Dryopteris
g) Homosporous ferns
5. Flask shaped structure 6. Cordate gametophyte
i) Archegonia a) Prothallus
7. Unicellular and spirally coiled 2 flagellated structure
j) Antherozoids
8. Dominant phase of Pteridophytes d) Sporophytic generation 9. Spores 10. Leaf
f) Haploid phase b) Frond
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