The Gymnosperms are a group of seed-producing plants (spermatophytes) that includes conifers (Pinophyta), cycads, Ginkgo, and gnetophytes. The term "gymnosperm" comes from the Greek composite word γυμνόσπερμος (γυμνός gymnos, "naked" and σπέρμα sperma, "seed"), meaning "naked seeds". The name is based on the unenclosed condition of their seeds (called ovules in their unfertilized state). The non-encased condition of their seeds stands in contrast to the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or solitary as in Yew, Torreya, Ginkgo.
The gymnosperms and angiosperms together compose the spermatophytes or seed plants. The gymnosperms are divided into six phyla. Organisms that belong to the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta) phyla are still in existence while those in the Pteridospermales and Cordaitales phyla are now extinct.
By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). Roots in some genera have fungal association with roots in the form of micorrhiza(Pinus), while in some others(Cycas) small specialised roots called coralloid roots are associated with nitrogen fixing cyanobacteria.
Gnetum is a genus of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been proposed to have been the first plants to be insect-pollinated as their fossils occur in association with extinct pollinating scorpion flies. Molecular phylogenies based on nuclear and plastid sequences from most of the species indicate hybridization among some of the Southeast Asian species. Fossil-calibrated molecular-clocks suggest that the Gnetum lineages now found in Africa, South America and Southeast Asia are the result of ancient long-distance dispersal across seawater
Sphenophyllum was a scrambling plant that formed dense thickets from the Late Devonian to late Permian periods. It had delicate, branching woody stems bearing whorls of heterophyllous leaves with morphology dependent on branch order. Whole plant reconstructions are limited due to rare preservation of roots. Sphenophyllum had a protostelic stele and tracheids with bordered pits. Reproduction occurred via cones like Bowmanites with whorls of fused bracts bearing sporangiophores and sporangia containing homosporous spores.
Pentoxylales were small trees or shrubs that existed in the Jurassic period in India. They had long and short shoots resembling Ginkgo, with spirally arranged leaves and scales. The stems (Pentoxylon) had five triangular segments around a central tissue. Leaves (Nipaniophyllum) were strap-shaped with a midrib. Male cones (Sahnia) bore pollen sacs on short shoots. Female cones (Carnoconites) had ovules aggregated into strobili on short shoots. Stomata were syndetochelic. Wood was pycnoxylic, resembling conifers. Pentoxylales displayed features intermediate between ferns
Selaginella, commonly known as club moss or spike moss, is a genus of vascular plants that has worldwide distribution, especially in tropical regions. It reproduces both sexually and asexually. The plant body is differentiated into roots, stems, microphyllous leaves, and ligules. The stems are green and branched. Microspores and megaspores are produced in sporangia and develop into male and female gametophytes, respectively, through precocious germination. Fertilization occurs when sperm from the male gametophyte fuses with eggs in the female gametophyte, forming a diploid sporophyte.
This document provides an overview of gymnosperms, including their general characters, classification, and examples. It discusses how gymnosperms are woody, vascular plants whose seeds are not enclosed in fruits. They are classified into 5 orders - Cycadales, Coniferales, Ephadrales, Gnetales, and Ginkgoales. Examples like cycas, conifers, ephedra, gnetum, and ginkgo biloba are described. The classification system proposed by David Bierhost in 1971 is outlined.
- Rhynia was a genus of early vascular plants that lived in the Devonian period, around 390-374 million years ago. It had branching, leafless aerial stems that grew from horizontally creeping underground rhizomes.
- The plant's internal structure included an epidermis, cortex with photosynthetic cells, and a protostelic vascular cylinder. Reproduction occurred through sporangia borne on branching tips, containing spores that likely developed into multicellular gametophytes.
- Two species were identified, R. major and the smaller R. gwynne vaughani, though the distinction between sporophyte and gametophyte generations required further clarification based on the fossil
This document provides an overview of the classification of gymnosperms by different researchers over time. It discusses the key characteristics of modern gymnosperms and describes the four orders that living gymnosperms are commonly grouped into: Cycadales, Ginkgoales, Coniferales, and Gnetales. For each order, it highlights some representative genera and provides details on morphological features. The classification schemes of various scientists who studied gymnosperms, such as Bentham and Hooker, Engler, Coulter and Chamberlain, are summarized. Diagrams of their classification systems are also included.
The document discusses the evolution of steles, or vascular bundles, in pteridophytes. It describes the basic types as protostelic and siphonostelic. Protostelic steles have central xylem and surrounding phloem with no pith, while siphonostelic steles have a central pith. Specific protostelic types include haplostele, actinostele, and plectostele. Siphonostelic types include cladosiphonic, phyllosiphonic, ectophloic, amphiphloic, solenostele, dictyostele, and polycyclic steles. The origin of
Heterospory and seed habit in pteridophytes.
Heterospory originated from some spores degenerating in sporangia, allowing the surviving spores to grow larger. This led to megaspores producing female gametophytes and microspores producing male gametophytes. In heterosporous plants like Selaginella, the retention and germination of megaspores inside megasporangia brought them closer to seed habit, though true seeds did not form until gymnosperms evolved integuments around ovules. Heterospory played a significant role in the evolution of seed habit and seeds in higher plants by establishing dependencies that facilitated embryogenesis.
Stelar evolution in Pteridophytes-BOTANYANJALIJAYAN6
Pteridophytes are vascular plants that reproduce via spores. They have a number of shared characteristics including lignified cell walls, tracheary elements, and an independent sporophyte generation. The stele, or central vascular cylinder, of pteridophytes can take several forms. The protostele is the simplest form, with a central xylem core surrounded by phloem. More advanced forms include the siphonostele, with a central pith, and the dictyostele, with overlapping leaf gaps. The eustele features a ring of vascular bundles around the edge of the pith.
This document discusses anomalous secondary growth in plants. It begins by defining anomalous secondary growth as a deviation from normal cambial activity in dicots. There are two types of anomalous growth: adaptive and non-adaptive. Adaptive growth includes woody climbers, while non-adaptive includes plants like Rumex and Chenopodium.
The document then describes two types of anomalous secondary growth: 1) abnormal behavior of the normal cambium and 2) abnormal behavior of an abnormal cambium. In type 1, the cambium forms vascular tissue only in bundle regions or produces more vascular tissue in bundles, seen in plants like Cucurbita and Bignonia. In type 2, accessory cambia form rings of vascular bundles
Classification denotes the arrangement of a single plant or group of plants an distinct category following a system of nomenclature, and in accordance with a particular and well established plan.
This document discusses apogamy and apospory in plants. It defines apogamy as asexual reproduction in ferns where a haploid gametophyte develops into a haploid sporophyte without gamete fusion. Apospory is defined as the development of a diploid gametophyte from the vegetative cells of a diploid sporophyte, without meiosis or spore formation. The key difference between the two is that apogamy produces a haploid embryo while apospory produces a diploid embryo. Causes of each include environmental stresses that prevent normal sexual reproduction. Similarities include that both are asexual reproductive processes that occur in bryophytes and involve alternation of generations
"Equisetum" Structural development Reproduction Muhammad ArSlan
The plant body of Equisetum has an underground rhizome and an aerial shoot. The shoot has scale-like leaves arranged in whorls and ridges with stomata located in furrows. It reproduces sexually through antheridia and archegonia on separate gametophytes. Upon fertilization of the egg, the zygote develops into a four-celled embryo that grows into a new sporophyte, with multiple sporophytes potentially developing from a single gametophyte.
The document discusses several theories about the origin and evolution of angiosperms. It describes theories that proposed various plant groups as possible ancestors of angiosperms including isoetes, conifers, gnetales, bennettitales, caytoniales, and pentoxylales. However, many of these theories were later contradicted or disagreed with based on evidence from vascular anatomy, seed structure, and other characteristics. The document also outlines primitive and advanced characteristics seen in different angiosperm groups, showing their diverse evolutionary lines.
- Gnetum is a genus of gymnosperms that are tropical evergreen trees, shrubs, and lianas. Unlike other gymnosperms, they possess vessel elements in their xylem.
- There are approximately 35 species of Gnetum distributed mainly in tropical and humid regions of Africa, Asia, and South America. Five species are reported in India.
- Gnetum reproduces sexually as a dioecious plant. The male and female strobili (inflorescences) are compound structures composed of bracts and rings of male or female flowers. Pollen grains contain two nuclei that develop into the male gametophyte within the anther.
Cycas is a gymnosperm that reproduces both vegetatively and sexually. Vegetative reproduction occurs through adventitious buds on the stem base that develop into new plants. Sexual reproduction involves separate male and female plants that produce cones. Pollen from the male cone is transferred to female cones by wind. After fertilization, the ovule develops into a seed protected by a fleshy outer layer and stony middle layer. The seed germinates by rupturing at the micropyle and producing a radicle and plumule to form a new sporophyte plant.
1. Selaginella is a heterosporous plant that produces megaspores and microspores. The spores develop into male and female gametophytes within their spore walls.
2. Microspores develop into male gametophytes containing antherozoids for fertilization. Megaspores develop into female gametophytes containing archegonia.
3. Fertilization occurs when antherozoids enter the archegonia through openings in the neck canal cells. This leads to the development of a diploid sporophyte within the megaspore.
Pteridophytes are classified into 4 divisions - Psilophyta, Lycophyta, Sphenophyta, and Pterophyta. Psilophyta includes the most primitive whisk ferns and Lycophyta includes club mosses and spike mosses. Sphenophyta contains the single living genus Equisetum, or horse tails. Pterophyta, or ferns, is the largest and most widely distributed division containing many families and over 10,000 living species distributed worldwide. Each division contains multiple classes that further specify characteristics such as plant body structure, leaf and spore structures, and reproductive systems.
Economic and Ecological Importance of Bryophytes.pptxDilip Gavande
Bryophytes have both ecological and economic importance. Ecologically, they are important for peat formation, providing food and shelter for animals, soil conservation by preventing erosion, tolerance of pollution like sulfur dioxide, and serving as indicators of acid rain. Economically, they are a source of fuel as peat, can be used as preservative agents, have medicinal uses, can be grown as ornamental plants, and have household uses like insect repellents.
Lycopodium is a genus of small herbaceous or shrubby plants classified in the division Lycophyta. The modern representatives are small compared to related plants from the Carboniferous period that grew as large trees. Lycopodium species have small, simple leaves and produce homosporous sporangia. They have a heteromorphic life cycle with a subterranean gametophyte generation. Lycopodium species are found worldwide in tropical and subtropical forests. Some grow as epiphytes in the tropics. Traditional herbal medicine uses certain Lycopodium species.
- Anthoceros is a genus of about 200 species of hornworts that are terrestrial and cosmopolitan.
- They grow in very moist and shady places like slopes, rocks, or sides of ditches. Some species are also found growing on decaying wood.
- Anthoceros reproduces both vegetatively through tubers, gemmae, and persistent apices, and sexually through antheridia and archegonia leading to the formation of sporophytes and spores.
Gymnosperms definition
Morphological characters of Gymnosperms
Anatomy of Gymnosperms
Cycas
General character of cycas
Sexual reproduction in cycas
Asexual reproduction in cycas
Economical importance of cycas
Pinus
Characters of pinus
Sexual reproduction in pinus
Asexual reproduction in pinus
Importance of pinus
Roots anatomy
Stem anatomy
Xylem
Phloem
1. The document describes the life cycle and morphology of the moss Funaria. It has a haplontic and diplontic life cycle with alternation of generations exhibiting heteromorphy.
2. The gametophyte generation is the dominant phase and reproduces sexually or asexually. Sexual reproduction involves antheridia and archegonia that produce gametes for fertilization.
3. Fertilization leads to formation of a sporophyte which grows from the archegonium. The sporophyte bears spores in capsules and releases them to complete the life cycle.
The document discusses the morphology, anatomy, and reproductive structures of gymnosperms. It focuses on Cycas, describing its external morphology such as its unbranched stem covered in persistent leaf bases and pinnately compound leaves. Internally, it notes Cycas has monoxylic wood and coralloid roots that form a symbiotic relationship with cyanobacteria. It also details the structures and development of male and female reproductive organs in Cycas, which are dioecious and wind pollinated. Cycas reproduces sexually through seeds and vegetatively through bulbils.
The document provides information about gymnosperms, including their characteristics, evolution, and representative groups. Some key points:
- Gymnosperms are seed plants with exposed ovules, in contrast to angiosperms which have enclosed seeds. They include conifers, cycads, gnetophytes, and ginkgo.
- They evolved from non-seed producing ancestors over 300 million years ago. Today there are over 1,000 living gymnosperm species in 14 families.
- Coniferophyta is one of the largest gymnosperm groups. It includes conifers which reproduce via pollen and cones. Representative families are Pinaceae, Araucariaceae, Podocarp
1. Gymnosperms are naked seeded non-flowering plants that show alternation of generations between sporophyte and gametophyte stages. The sporophyte plant body is well differentiated into roots, stems, and leaves while the gametophyte is greatly reduced.
2. Gymnosperms reproduce sexually through cones that contain either microsporangia or megasporangia. Pollination occurs and pollen tubes carry sperm to fertilize eggs within the ovules, forming seeds with embryos.
3. The life cycle involves microspores forming male gametophytes that produce sperm, and megaspores forming reduced female gametophytes containing eggs. Fertilization occurs
Gnetum is a genus of approximately 30 species of dioecious, mostly liana plants found in tropical and subtropical regions worldwide. The document discusses the systematic classification, morphology, anatomy, reproduction, life cycle and other aspects of Gnetum. Key points include:
- Gnetum is classified in the division Gnetophyta. Five species are found in India.
- Plants are mostly lianas with leaves resembling dicot leaves in structure. Stems also resemble dicot stems anatomically.
- Reproduction is sexual and dioecious. Male and female cones are composed of bracts and flowers. Pollination occurs through pollen carried by ants.
This document provides information about the genus Pinus. It discusses the systematic position of Pinus, describing that it is in the division Gymnospermae, class Coniferopsida, order Coniferales, and family Pinaceae. It then discusses the geographical distribution, morphology, internal stem and leaf structure, reproduction, development of microsporangium and female cone, structure of ovule, pollination, embryology, and germination of Pinus. Key details include that Pinus is widely distributed in the Northern hemisphere, has scale and needle-like foliage leaves, and reproduces through monoecious cones that produce microspores and megaspores through meiosis.
- Ginkgo biloba is an ancient tree species known as a living fossil. It is one of the oldest seed plant species still in existence today.
- The tree has distinctive fan-shaped leaves and produces seeds and cones. It is dioecious, with separate male and female trees.
- Ginkgo biloba has been used in traditional Chinese medicine and its extracts may help with conditions like vertigo and cerebral insufficiency. It is also considered a sacred tree in some Asian cultures.
• Gymnosperms (Gymnos = naked, Sperma = seed) include the small group of plants with naked seeds.
• The Gymnosperms originated in the Devonian period of the Paleozoic Era and formed the supreme vegetation in the Mesozoic Era.
This is a Life Cycle of Shpagnum, A good content for Masters Students. (But this content is not made by me...but i thought that this will help many students who are in search for content)
Thank you 😊
MARSILEA notes in detail for II year Botany.pptaigil2
This document describes the systematic position and characteristic features of the genus Marsilea. It is a heterosporous aquatic fern that belongs to the order Marsileales. It produces sporocarps that contain microsporangia and megasporangia. There are about 65 species distributed worldwide in tropical regions like Africa and Australia. The document outlines the external morphology, anatomy, reproduction and life cycle of Marsilea. It alternates between a diploid sporophytic generation and haploid gametophytic generation through the production of microspores and megaspores.
Structure, reproduction, life history and systematic position of LycopodiumSankritaShankarGaonk
This document provides information on the systematic position, morphology, anatomy, reproduction, and life cycle of Lycopodium. It discusses that Lycopodium has 400 species found in varied habitats worldwide, including in India. It has dichotomously branched stems and leaves without ligules. Reproduction occurs vegetatively and via spores. Spores form in structures called strobili and develop into homothallic gametophytes that produce both antheridia and archegonia for sexual reproduction. The life cycle involves a diploid sporophyte and haploid gametophyte generation.
1. Thuja orientalis is an evergreen tree native to Central Asia that is commonly cultivated as an ornamental plant.
2. It can reach heights of 15 meters but is often trimmed in gardens to remain bushy.
3. The plant is dioecious, with male and female cones developing on separate branches. Female cones contain 1-3 wingless ovules that develop into seeds if fertilized by pollen from the male cones.
This document summarizes key aspects of bryophytes, pteridophytes, and gymnosperms. Bryophytes reproduce sexually through male and female sex organs on the same or different thalli, with the sporophyte producing spores within a capsule. Mosses have a protonemal stage and leafy shoot stage. Pteridophytes are the first plants with vascular tissue and reproduce via sporangia producing spores that germinate into gametophytes. Gymnosperms are heterosporous with pollen grains fertilizing archegonia within ovules, forming naked seeds without an ovary wall.
The document describes the order Marsileales. It belongs to the division Pterophyta and class Leptosporangiopsida. Marsileales contains a single family Marsileaceae with 3 genera, most species belonging to Marsilea. It includes small heterosporous ferns that grow in water or wet places. Members have creeping rhizomes with erect leaves on long petioles. Sporangia are produced in hard, bean-shaped sporocarps. Each sorus contains both microsporangia and megasporangia. The life cycle and reproductive structures like sporocarp, sporangium and gametophytes are described in detail.
Similar to Gnetum: A Powerpoint Presentation on Gymnospems (20)
How to Store Data on the Odoo 17 WebsiteCeline George
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It includes defining a model with few fields in it. Add demo data into the model using data directory. Also using a controller, pass the values into the template while rendering it and display the values in the website.
Front Desk Management in the Odoo 17 ERPCeline George
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AI Risk Management: ISO/IEC 42001, the EU AI Act, and ISO/IEC 23894PECB
As artificial intelligence continues to evolve, understanding the complexities and regulations regarding AI risk management is more crucial than ever.
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• ISO/IEC 42001 standard, which provides guidelines for establishing, implementing, maintaining, and continually improving AI management systems within organizations
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Callum Wright is a seasoned cybersecurity, privacy and AI governance expert. With over a decade of experience, he has dedicated his career to protecting digital assets, ensuring data privacy, and establishing ethical AI governance frameworks. His diverse background includes significant roles in security architecture, AI governance, risk consulting, and privacy management across various industries, thorough testing, and successful implementation, he has consistently delivered exceptional results.
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Tags: ISO/IEC 42001, Artificial Intelligence, EU AI Act, ISO/IEC 23894
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The Jewish Trinity : Sabbath,Shekinah and Sanctuary 4.pdfJackieSparrow3
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Principles of Roods Approach!!!!!!!.pptxibtesaam huma
Principles of Rood’s Approach
Treatment technique used in physiotherapy for neurological patients which aids them to recover and improve quality of life
Facilitatory techniques
Inhibitory techniques
3. :
naked seed producing vascular plants.
include conifers, cycads, ginkgo(The “LIVING FOSSIL” plant)& gnetales.
seeds develop on the surface of scale like appendages of cones/strobili.
more advanced than ferns as they produce seeds and in their case the
sporophytic generation dominates over the gametophytic counterpart.
4. There are about 700 to 900 extant* species of Gymnosperms.
(Note: Extant- term refers to taxa still found to be living.)
Gymnosperms originated in late carboniferous period.
They are considered to be the result of genome duplication
event which took place around 319 Mya.
The fossils of Pro-gymnosperms, belonging to late Devonian
period around 383 Mya, exhibit some characters found in the
gymnosperms.
By the end of the Palaeozoic era, they replaced most of the
ferns becoming the dominant vegetation of the Mesozoic era.
The end of Mesozoic era marked start of their extinction.
8. Classic Classification Of Gymnosperms
Chamberlain (1935), in his book gymnosperms-structure and evolution, divided
gymnosperms into 2 main groups, i.e. Cycadophytes and Coniferophytes as
mentioned below:
Of all the above mentioned orders; cycadofilicales, bennettitales of cycadophytes and cordiatales of coniferophytes are
extinct.
The order coniferales of coniferophytes was further divided into 6 families namely;
Abietacaceae,Taxodiaceae,Cupressaceae,Araucariaceae,Podocarpaceae,Taxaceae.
Gymnosperms
Cycadophytes
Cycadofilicales
E.g.:
Lygenopteris
(extinct)
Bennettiales
E.g.:
Cycadeoidea
(extinct)
Cycadales
E.g.:
Cycas,
Microcycas,Zamia,
Stangeria
Coniferophytes
Cordiatales
E.g.:
Cordaites
(extinct)
Ginkgoales
E.g.:
Ginkgo
Coniferales
E.g.:
Pinus,
Abies,Taxus
Gnetales
E.g.:
Gnetum
9. MODERN CLASSIFICATION OF GYMNOSPERMS
Cycadales and Ginkgoales include living members which have long fossil history and are thus regarded as
“living fossils”, example G.biloba.
Coniferales include abies, taxus, pinus. The gnetales represented by 3 genera example gnetum, ephedra
and Welwitschia mirabilis.
Gymnosperms
Cycadophyta
Ginkgophyta
Coniferophyta
Gnetophyta
11. CYCADOPHYTA : CYCADS
: Dioecious
Originated in Carboniferous period from seed ferns i.e. Cycadofilicales & were dominant veg. during Mesozoic era.
• Include 11 genera & 100 species; mostly woody with
monoxylic trunk except Zamia pygmea.
Stem/Caudex : unbranched with leaf scars
Leaves/Frond: pinnately compound, arranged in whorls;
found in crown/apex region of stem.
• Roots are coralloid type with primary & secondary divisions.
• Microsporophyll form male strobili.
Megasporophyll form female strobili.
13. Coniferophyta: Conifers
• Largest division of gymnosperms including pinus,yews,spruces,junipers,cedars,etc.
• Most diverse with 588 extant species; both economically/ecologically important.
• They are long, branched and evergreen trees with dimorphic branches.
• Leaves: may be comb-like, scale-like, needle-like; mostly linear.
• Wood usually pycnoxylic characterised by presence of resin canals.
• Microsporophylls and megasporophylls form compact cones; that are distinguishable.
• Male Gametes -non motile; found in ♂ cone
• Fertilization – Siphonogamous type.
15. Ginkgophyta : Ginkgo
Ginkgo biloba : MAIDEN HAIR TREE
Only living species of Ginkgophyta; thus also k/a “living fossil.”
First ancestor dated Permian Era; although originated in Jurassic period.
First discovered in South East China, preserved in a sacred garden.
Leaves: Fan-shaped, varied morphology – deep lobed(notched) to unlobed,
parallel veins; exhibiting open dichotomous venation.
Dioecious; Male Trees with stalked pollen sacs together at leaf base
Female Trees with pair of naked ovules at end of long stalk.
G.biloba alongwith Cycads are only living seed plants with flagellated
male gametes.
Rotting fruit produce foul smell due to production butyric acid.
19. Division Gnetophyta is classified into class Gnetopsida which includes orders i.e. Gnetales,
Welwitschiales and Ephedrales. Gnetales comprises of Family Gnetaceae which includes
Genus Gnetum having about more than 30 species. Similarly, Welwitschiales and Ephedrales
comprise of families Welwitschiaceae and Ephedraceae respectively. These families
Welwitschiaceae and Ephedraceae are further divided into Genus Welwitschia, with only
single Mirabilis species,& Genus Ephedra comprising of more than 50 species respectively.
Gnetophyta
Gnetales Gnetaceae Gnetum 30+ Species
Welwitschiales Welwitschiaceae Welwitschia Mirabilis
Ephedrales Ephedraceae Ephedra 50+ Species
Division Class Order Family Genus Species
21. Systematic Position:
Division : Gnetophyta
Class : Gnetopsida
Order : Gnetales
Family : Gnetaceae
Distribution: Represented by 40 species; confined to tropical & humid regions.
According to Bhardwaj (1957),mainly 5 gnetum species in India.
•
•
•
•
•
22. Characteristic Features Of Gnetum
Most Species are climbers except few being shrubs & trees.
Branches 2 types : Branches of limited growth
Branches of unlimited growth
Climbing Species have branches of limited growth (short shoots)
and unbranched with foliage leaves.
Leaves: Dicot like scaly leaves; large & oval with entire margins
9-10 in pairs arranged in decussate fashion with
reticulate venation.
23. Anatomy Of Gnetum
(a) Roots
InYoung Roots :
1) Layers of starch filled cortical cells.
2) 4-6 layers of pericycle; primary xylem visible.
3) Roots may be Di-arch and Ex-arch (Angiospermic Ch.).
In Older Roots :
1) Primary xylem indistinguishable due to 2ndry growth.
2) Consists of tracheids, vessels & xylem parenchyma.
3) Phloem consists of sieve tubes & phloem parenchyma.
4) “Bars of Sanio” present in tracheids; absent in vessels.
27. Microsporangium : Microsporogenesis
1) 2archesporial cells divide to form multi-celled archesporium.
2) Archesporium divide periclinally forming:
Outer Layer: Parietal cells
Inner Layer: Sporogenous cells
3) Parietal cells form tapetal cells periclinally.
4) Sporogenous cells divide irregularly forming MMC.
5)Tapetal cells get bi-nucleated.
6) MMC form haploid microspores by meiosis; soon,
wall cells & tapetal cells of tapetum disorganise.
7) As soon as the anthers dehisce(along the double
row of small cells which extends from tip towards the base),
the microspores are released.
28. Megasporangium : Megasporogenesis
• 2 archesporial cell divide periclinally forming outer parietal cells & inner sporogenous cells.
• Primary Parietal Cells & Epidermal Cells divide periclinally & anticlinally many times forming
nucellus.
• Sporogenous cells by repeated division form MMC.
• MMC by meiosis form tetrasporic embryo sacs
(out of which 1 remains functional, others degenerate)
• Finally, ♀ gametophyte is formed which is broader at
micropylar end and tapering at chalazal end.
Note: In Gnetum, Normal Archegonia &
Megaspore tetrad are absent.
29. Pollination, Fertilization And Post Fertilization
• Pollination : Pollens pollinated by anemophily; get entangled to fluid
secreted by micropylar tube thereby male gametes reach egg chamber.
• Fertilization : Pollen tube breaks into ovule releasing male cells. 1 cell enters egg cell.
Male and Female nuclei, lie side by side for sometime, then fuse to form zygote.
• Endosperm Formation : In Gnetum, cellular endosperm formed after fertilization although
cell formation starts after fertilization ( usually in gymnosperms endosperm develop before fertilization)
After fertilization, wall formation starts from base
and proceeds upward such that cytoplasm divides
into many compartment containing many nuclei,
which fuse to form a single nucleus.The upper (B)
portion usually remains free- nuclear while lower (A)
portion becomes cellular having multi nucleated
compartment.The vice-versa may also be possible
and in some rare cases no wall formation may take
place.Triple Fusion(found in angiosperm) is absent.
30. Embryo In Gnetum
• In Gnetum, different species show variable embryonal development.
(Acc. to Maheshwari &Vasil, the first division of zygote in angiosperms is accompanied by wall formation
while in gymnosperms(except Sequoia spp.),free nuclear division.Thus, Gnetum in this respect forms a link b/w
gymnosperms and angiosperms as it shows both free nuclear division & cell division.)
• Acc. to Madhulata(1960), in G.gnemon: out of 2-4 zygotes, 1 remains functional and develops 1 or 2-3 small
tubular outgrowths,out of which only 1 receives nucleus while other disintegrates.The surviving outgrowths or PST
primary suspensor tubes coil around each other. A small
cell cuts off at the tip of PST, divides 1st transversely &
then longitudinally giving 4 cells which divide to form
cell mass. Some of it’s cells elongate/divide to form SST
or Secondary SuspensorTube while other cells form
EM i.e. Embryonal Mass.The Primary and Secondary
Suspensor helps in pushing embryo to endosperm.
At the end of pushing, stem tip with 2 lateral cotyledons
is formed at tip of EM while root tip with root cap is
formed at opp. side; thereafter feeder develops b/w the
root & shoot portion such that the resultant Mature
Embryo consists of stem tip, two cotyledons root tip &
root cap in respective sequence.
31. Germination Of Seed In Gnetum
Seeds in Gnetum: i) Oval shaped, green to red in colour
ii) Surrounded by 3-layered envelope enclosing Embryo & Endosperm:
# Inner Envelope : Parenchymatous
# Middle Envelope : Hard Protective
# Outer Envelope : Fleshy, parenchymatous, coloured
Seed Germination: i) Epigeal Type
ii) Hypocotyl elongates bringing cotyledons out of soil.
iii) First pair of foliage leaves produced by develop. plumule.
33. Resemblance b/w Gnetum & Angiosperms
– Following features are common in Gnetum & Angiosperms:
i)Reticulate venation in leaves.
ii)Presence of xylem vessels.
iii)Tetrasporic development of ♀ gametophyte.
iv)Absence of Archegonia.
v)Dicot nature of Embryo.
G.ula Leaf Section J.sambac Leaf Section
34. Resemblance b/w Gnetum & Gymnosperms
• Following features are common in Gnetum & Gymnosperms:
– Presence of wood with tracheids having bordered pits.
– Presence of Anemophily mode of Pollination
– Presence of naked Ovule.
– Absence of ovary thus fruit absent.
– Development of prothallial cell.
– Presence of Cleavage Polyembryony.