First Vascular plant in land , Pteridophytes.

 

• The plant kingdom is divided into two groups: Cryptogams and phanerogamae.

• Cryptogams are those that are reproduced by means of spores.

• They  do not produce any type of seed. The algae and  fungi are kept under cryptogams along with the  bryophytes and pteridophytes. 

• The pteridophytes are  used in medicine and prevent soil erosion by acting as a soil binders.

• They are also used as ornamental plant. They are first terrestrial plant having vascular tissue like xylem and phloem.

• The pteridophytes are  vascular cryptogams as they have a well developed conducting system of tissue.

• Vascular cryptogams are seedless vascular plants that have successfully invaded the land.

• The Pteridophytes appeared on earth around 280 to 250 million years ago.

• Pteridophytes grow in a variety of habitats which are mostly terrestrial.

• They grow well in abundant moisture conditions and shade  areas but some like  Selaginella lepidophylla,

• Gleichenia can grow   well in xerophytic or sandy soil   conditions. In addition to this, few are found in  aquatic conditions like Marsilea, Salvinia, Azolla.

• Some Members  are grown as  epiphytes such as Selaginella oregana, Lycopodium phlegmaria.

• Some Pteridophytes are also exist as fossil like Rhynia, Hornea, Zosterophyllum.

General feature  of Pteridophytes

Sporophyte, Dominent stage 

• Sporophyte is the dominant phase in pteridophytes. Sporophyte is divided into root stem and leaves.

• All plant organ like Root, stem leaves possess vascular tissue like xylem and phloem.

• Pteridophytes are the first true land plants that successfully grow in land.

• Pteridophytes are seedless, vascular cryptogams.

• Stem is usually branched but branches do not arise in the axil of the leaves.

• In many Pteridophytes, the stem is represented by a rhizome. Roots are adventitious in nature. 

• Leaves may be small and  thin termed as  microphyll like Equisetum and Selaginella.

• In Fern Dryopteris, Adiantum, leaves are  large and  pinnately called macrophyll. Young leaves of sporophyte show circinate vernation.

Sporangia 

• The leaves of pteridophytes   bearing the sporangia are termed as sporophylls.

• Spores are produced in sporangia through meiosis. Spores are homosporous or heterosporous.

• The  spores  that are formed of similar size and one type   are termed as  homosporous whereas in heterosporous conditions, two kinds of spores are produced.

• Sporangia are produced in groups on sporophylls.

• Sporangia may be borne either on stem or leaves.

• On leaves, sporophyll  are located marginally  like Pteris, Adiantum.

• On the stem they are located terminally like  Rhynia and in Lycopodium they are found at  lateral position. 

Prothallus formation

• In Equisetum and selaginella the sporangia are borne on special structures called sporangiophores. Such sporangia is called cone or strobli.

• In Marsilea, Azolla, Salvinia sporangia are produced in sporocarps. Sporangia produce spores by meiosis from the spore mother cell.  

• These spores on germination give rise to inconspicuous, small multicellular and free living, thalloid gametophytic bodies called Prothallus.

• In homosporous Pteridophytes prothallus are monoecious or antheridia and archegonia develop on the same prothallus.

• In heterosporous species, prothalli are always dioecious.

• Microspores on germination give rise to male prothallus and megaspores gives rise to the female prothallus.

Gametophyte 

• As described earlier, Antheridia and archegonia are developed on prothallus or Gametophyte.

• Antheridium is surrounded by sterile jackets. Fertilization results in the formation of zygote which ultimately develops into a well-developed sporophyte.

• Plants show  alternation of generation like bryophytes. but in pteridophytes,the main plant body is sporophytic. and forms a dominant phase in the life cycle.

Reproduction

• Gametophyte stages bear Antheridia and Archegonia in the form of male and female gametes.

• Antheridia produce male gametes called antherozoids.

• These Antherozoids are moved by using water as a medium at the mouth of Archegonium.

• In archegonium there is an egg that fuses with the male gamete and forms zygote.

• Later on, zygote produces a multicellular sporophyte, a dominant phase of pteridophyte.

Precursor Seed habit in Pteridophytes.

• In selaginella and salvinia, two kinds of spores are produced in sporophyte: one is large and the other is small.

• These spores are termed as megaspore and microspore. The megaspore and microspore give rise to female and male gametophytes.

• In female Gametophyte, zygote is developed into embryo but it remains attached with sporophyte.

• This attachment of  gametophyte with embryo to sporophyte is regarded as precursor of seed habit in plant .

Stelar system

• The special arrangement of xylem and phloem in vascular bundle with or without pith along with cortex is called stele.

• Pteridophytes have well developed stele and well diversified stelar system .