Characteristics of Gymnosperms in Points

Gymnosperms term was given by “Theophrastus” in his book “Enquiry into plants”. Gymnosperm has been derived from Greek words. (Gymno = Bare/Naked) (Spermas = seeded).

Characteristics of Gymnosperms in Points

Characteristics of Gymnosperms in Points

Characteristics of Gymnosperms

The characteristics of gymnosperms are as follow.

Sub Groups of Spermatophytes 

According to “Geobel” known as “phanerogams”. (Hidden sex organs i.e. archegonium and Antheridium).

 

Sub Groups of Spermatophytes

They can survive for several years. They are perennials and ever green and woody in nature.

Annual or herbaceous  plants are absent in gymnospems.

Climbers

Epherdrs (olicus)

Gnetum ulva

Shrubs

Zamia  pygmaea  (3.5)  (smallest gymnoperm)

Tree

Sequoia  semperviens  (300 ft)

S.gigantea  (342 ft)

s.wellingtonia   (392 ft )

  1. Habitat

These are generally present in temperate regions where snow is the main source of water e.g. Pinus. Some are also found in tropical and sub tropical area e.g. Cycadales (order)  genetales.

  1. Sporophytic Plant Bodies (Root, Stem, Leaf)

This type of plant body is  differentiated into root, stem and leaves.

Sporophytic Plant Bodies

Types of Root

Adventitious root may be associated or non -associated.

Root Types

Types of Root

Depending upon the nature of microorganisms associated adventitious roots are

Types of Adventitious Roots

Stem

Unbranched

Branched

Caudex habit

Appearance of stem in cone like manner known as Excurrent habit e.g. coniferales
Unbranched stem with whorl of leaves at tip

It may be Dwarf (limited growth branch) and Tall (unlimited growth)

  
Leaf

The leaves present on the gymnosperm plant may be of only one or two kinds (Dimorphic leaves).

Leaf Types

Types of Leaves

Simple leaf

Compound leaves

Does not show circinate venation.

Show circinate venation.
Present at dwarf shoot.

Present at the top of stem as crown.

Coniferales (pinus)

Cycadales (cycas)

Leaf can tolerate extreme with respect to wind, temperature and humidity.

By adopting following are characteristics, surface area of leaf is reduced. E.g.  Needle leaves that will prevent water loss under dry condition.

Additionally, waxy layer formation at epidermis layer in leaf, that protects water loss by lowering evaporation.

There is presence of sunken stomata.

Most gymnospermic leaves do not lateral veins, instead of this; there is well developed transfusion tissue known as Hydrostereon. In cycas, leaves and less developed in pinus for lateral translocation of nutrients. The mesophyl of the leaves may be either

Types of Mesophyl

 

  1. Vascular Tissue in Gymnosperms

Xylem

Phloem

Tracheids

Depending upon the thickening tracheids has two types:

Sieve cell along with assistant albuminous cell is present. Sieve tube along with capnion cell is absent

1: mature (Bordered pits thickening)

2: young

Protoxylem (spiral thickening)

Metaxylem (sclariform)

Xylem fibers are present.

Vessels are generally absent.

  1. Wood

“Secondary xylem formed by cambium meristem through differentiation
(sec. meristem converts into sec. permanent tissue) is known as wood”.

Depending upon cambium ring wood has two types:

Monoxylic wood

Polyxylic wood

Type of wood which forms due to activity of first persistent cambium ring.

Type of wood which form due to more than one short lived cambium ring.

Example:

Ginkgoales

Gnetales

Coniferales

Codaitales

Example:

Cycadales (order)

Cycas  pectinata ( it have 20 cambium)

Cycadeoidales

 cycadofilicales

Monoxylic wood upon higher functioning of persistent one cambium ring to form high vascular tissue result in lowering of soft tissue.

Cortex

Pith

Upon lower functioning of short lived cambia, result in slightly lowering of soft tissue.

Cortex

Pith

At the stage Monoxylic wood is known as Pycnoxylic wood.

At this stage the wood is Monoxylic wood.
Wood without vessel is known as Homoxylous.Wood with vessel is known as Heteroxylic wood.
Example:

Generally, in all gymnosperms.

Example:

Gnetales

Gnetium

Ephedra

Wee witschia

 

  1. Woody Sporophylls

Specialized leaves containing with sporangia is known as sporophylls, which also woody in nature.

Depending upon size of leaves

Microsporaophyll

Megasporophylls
Small sized sporophylls with micro-sporangium.Large sized sporophylls with mega sporangium
Aggregate to form male cone due to formation

Pollen cone of microspore or male spore.

Aggregate to form female cone due to female spore formation, seed cone

Due to pollen grain formation inside the micro-sporangium.

Due to formation of seeds at this cone. It is megasporangiate cone due to formation of mega sporangium.

Both of these are also known as strobilus. Exceptional female cone of cycas is loosed strobilus known as Lax.

  1. Sexuality of cone

Unisexual cone

Pinus and cycas (either male or female).

Bisexual Cone

Picea excelra, Abler alra

  1. Female Cone in Gymnopserms

Long lived.

Larger in size.

Arrangement of megasporangium. (Ovule) in sorus (group of sporangium).

1-5 pairs of ovule in one sorus .e.g. cycas

Two ovules in one sorus. E.g. pinus
Present at lower surface of mega sporophylls.

Present at upper surface near the axis of megasporophyll.

Ovule

Generally, in all gymnosperms, ovule contains/bears one integument. Exceptional cases are as follow

Exceptional Cases

The ovule in all gymnosperms is orthotropous.

The integument is differentiated into three layers

Layer types

Types of Layers

The ovules are named in gymnospers i.e., they are not enclosed by an envelopw of megasporophylls.

The integument encloses nucellus with micropyle at the apex of ovule. The ovule contains one or several sporogenous cells (Megaspore Mother Cell). Each developing into linear row of four potential megaspores.

Only the lowermost megaspore is functionally behaves as functional megaspore or chalazal megaspore and forms embryo sac or prothallus (Female gametophyte).

Gametophyte

The plants are heterosporous. Both male and female gametophyte are very much reduced, dependent upon sporophyte.

  1. Male Cone in Gymnopserms

Short Lived

Smaller in Size

arrangement of microsporangium (pollen sac) in a group known a sorus.

3 to 5 sours

2 sorus
Which contains 900-1000 microsporangiumOne sorus contain 2 micro sporangium.
e.g. cycas

For example pinus.

Microsporangiums are always present at the lower surface of microsporophyll.

The development of microsporangium is eusporangiate (develop from a group of hypodermal cell).

Micro spores are generally without wings, exceptional pinus in which exine inflated to form balloon like expressions.

Male cone is large, bearing numerous sporophylls and present at the terminal end of main axis. Whereas pinus male cone is smallest at dwarf shoot.

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