Guys come and know about the General Characteristics of Gymnosperms | Notes. here we provide the sufficient and valuable knowledge about this concept.
• Mostly living gymnosperms are evergreen trees or shrubs with xerophytic adaptations.
• Plant body is sporophytic and differentiated into root, stem
• Stem in Gymnosperms :
Erect, Profusely branched (except Cycas) & woody.
• Presence of leaf scars on the stem is a characteristic feature of gymnosperms
Leaves are dimorphic.
Foliage leaves: green, simple, needle shaped or pinnately compound
Scaly leaves: minute & deciduous. Ephedra possesses only scaly leaves. Roots are di to polyarch.
• In the stem tanniniferous cells are frequently present
• Young stem has a ring of collateral and open vascular bundles.
• Xylem consists of trachieds & xylem parenchyma. Vessels are absent except in the members of Gnetales
• Phloem consists of sieve tubes & phloem parenchyma. Companion cells are absent
• Wood: Manoxylic in Cycas & Pycnoxylic in Pinus
Leaves with thick cuticle & sunken stomata. Mesophyll may be undifferentiated(Pinus) or differentiated into palisade & spongy parenchyma( Cycas)
• Most gymnospermic leaves don’t have lateral veins & lateral translocation takes place with the help of transfusion tissue.
• They are heterosporous – Megaspores & Microspores aggregate to form cones
• Cones : are usually monosporangiate except in Ephedra intermedia
• Male cones :-
short lived & microsporangia develop on the abaxial side of the microsporophyll
– No. varies from 2 (Pinus)to many(Cycas)
– development is eusporangiate
• Female cones:-
formed by the aggregation of megasporophyll
– remain persistent on the plant for several year
• The megasporangium (ovule) is a naked structure on the megasporophyll
• Ovules are orthotropous & unitegmic but bitegmic in Gnetales
• Ovular integument is three layered, outer and inner layers are fleshy & middle is stony
Microsporeare liberated in different developmental stages as: 3 celled in Cycas4 celled in Pinus 5 celled in Ephedra.
• Male gametes are non motile except in Cycas & Ginkgo.
• The no. of archegonia in a female gametophyte is variable as they are several in Cycas while only 2 in Pinus
• Archegonia has a single egg and venter canal cell; neck canal cells however absent
• Pollination is direct & all gymnosperms are wind pollinated •Fertilization is
• Zygote formed is the mother cell of next sporophytic generation & development of embryo is meroblastic.
• Development of endosperm is before fertilization and hence endosperm is haploid
• There is marked tendency of polyembryony, which may arise by fertilization of more than 1 eggs or by the division of the zygote but only 1 one embryo attains maturity.
• The naked ovule develops into seed & the ovular integument form seed coat
Classification by sporne(1965)
Gymnosperms are divided into three classes and nine orders:
- Manoxylic wood.
- Unbranched or poorly branched trunks.
- Leaves large and pinnate.
- Pycnoxylic wood.
- Large sized trees.
- Profusely branched stems.
- Simple leaves.
- Link between gymnosperms and angiosperms.
- vessels are present.
- companion cells are present.