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
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).
They can survive for several years. They are perennials and ever green and woody in nature.
Annual or herbaceous plants are absent in gymnospems.
Zamia pygmaea (3.5) (smallest gymnoperm)
Sequoia semperviens (300 ft)
S.gigantea (342 ft)
s.wellingtonia (392 ft )
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.
Sporophytic Plant Bodies (Root, Stem, Leaf)
This type of plant body is differentiated into root, stem and leaves.
Types of Root
Adventitious root may be associated or non -associated.
Depending upon the nature of microorganisms associated adventitious roots are
|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)
The leaves present on the gymnosperm plant may be of only one or two kinds (Dimorphic leaves).
Does not show circinate venation.
|Show circinate venation.|
|Present at dwarf shoot.|
Present at the top of stem as crown.
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
Vascular Tissue in Gymnosperms
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)
Protoxylem (spiral thickening)
Xylem fibers are present.
Vessels are generally absent.
“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:
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.|
Cycas pectinata ( it have 20 cambium)
|Monoxylic wood upon higher functioning of persistent one cambium ring to form high vascular tissue result in lowering of soft tissue.|
Upon lower functioning of short lived cambia, result in slightly lowering of soft tissue.
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.|
Generally, in all gymnosperms.
Specialized leaves containing with sporangia is known as sporophylls, which also woody in nature.
Depending upon size of leaves
|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.
Sexuality of cone
Pinus and cycas (either male or female).
Picea excelra, Abler alra
Female Cone in Gymnopserms
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.
Generally, in all gymnosperms, ovule contains/bears one integument. Exceptional cases are as follow
The ovule in all gymnosperms is orthotropous.
The integument is differentiated into three 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).
The plants are heterosporous. Both male and female gametophyte are very much reduced, dependent upon sporophyte.
Male Cone in Gymnopserms
Smaller in Size
arrangement of microsporangium (pollen sac) in a group known a sorus.
3 to 5 sours
|Which contains 900-1000 microsporangium||One sorus contain 2 micro sporangium.|
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.