Question

Tell about pteridophyta and its classification

Answer 1

(v) They are usually spirally arranged, sometimes in opposite fashion and or even in whorls.

(vi) In some cases the leaves are ligulate (e.g., Selaginella, Isoetes). The ligule is present at the base of each leaf.

(vii) The vascular tissue may be either in the form of plectostele, siphonostele or sometimes even polystele.

(viii) Leaf gaps are absent.

(ix) Sporangia are quite large in size and develop on the adaxial surface of the leaves (sporophylls).

(x) Sporophylls are loosely arranged and form strobilus.

(xi) Some members are homosporous (e.g., Lycopodium) while others are heterosporous (e.g., Selaginella).

(xii) Antherozoids are biflagellate or multiflagellate.

(xiii) Gametophytes which are in the form of prothalli are formed by the germination of spores.

(xiv) Heterosporous forms have endoscopic gametophytes while in homosporous forms the gametophyte is exoscopic.

(3) Sphenopsida:

(i) It includes both fossil plants (e.g., Calamophyton, Sphenophyllum) as well as living plants (e.g., Equisetum). It is represented by one living genus Equisetum and 18 fossil forms.

(ii) These Pteridophytes evolved during the Carboniferous period of the Palaeozoic era.

(iii) The plant body is sporophytic and can be differentiated into root, stem and leaves.

(iv) The stem in majority of the forms is long, jointed or articulated and is ribbed i.e., having ridges and grooves.

(v) Stem is divisible into nodes and internodes and is developed as upright aerial branches from the underground creeping rhizome.

(vi) Leaves are thin, small, scaly brown and are arranged in transverse whorls on the nodes of the aerial branches.

(vii) Branches also develop in whorls from the axil of the scaly leaves.

(viii) As the foliage leaves are reduced to scales, the process of photosynthesis is taken up by the stem and hence it becomes green.

(ix) The stem has a solid protostele (e.g., Sphenophyllum) or medullated protostele (e.g., Equisetum).

(x) Secondary thickenings were observed in some extinct forms (e.g., Sphenophyllum).

(xi) Sporangia are developed at the apex of the fertile branches in whorls forming compact cone.

(xii) Living members are homosporous but some fossil forms are heterosporous (e.g., Catamites).

(xiii) Spores germinate to give rise to gametophytes (prothalli) which may be monoecious or dioecious.

(xiv) Antherozoids are large and multiflagellate.

(xv) Embryo is without suspensor.

(4) Pteropsida:

(i) This sub-division includes the plants which are commonly known as ‘ferns’. It is represented by about 300 genera and more than 10000 species.

(ii) These Pteridophytes were originated during the Devonian period.

(iii) They occur in all types of habitats. Majority of the ferns are terrestrial and prefer to grow in moist and shady places. Some are aquatic (e.g., Azolla, Salvinia, Marsilea), xerophytic (e.g., Adiantum emarginatum), epiphytic (e.g., Asplenium nidus), halophytic (e.g., Acrostichum aureum) or climbing (e.g., Stenochlaena).

(iv) Some members are very small while some members are tall tree like (e.g., Angiopteris).

(v) Majority of the members (except some tree ferns e.g., Angiopteris) have short and stout rhizome. The rhizome may be creeping, upright or growing above the soil.

(vi) Leaves are large, may be simple (e.g., Ophioglossum) or compound (majority of the ferns for example, Pteridium, Marsilea, Adiantum etc.) and described as fronds.

(vii) Young fronds are circinately coiled.

(viii) Leaves are exstipulate (e.g., Filicales) while stipulate in some other groups.

(ix) The vascular cylinder varies from a protosete to a complicated type of siphonostele.

(x) Vegetative reproduction takes place by fragmentation (e.g., Adiantum, Pteridium), stem tubers e.g., Marsilea), adventitious buds (e.g., Asplenium bulbiferum) or by apogamy (e.g., Marsilea).

(xi) Sporangia arise from placenta (a swollen cushion of cells) in groups (sori).

(xii) Sori develop on the margins or abaxial surface of the leaves (sporophylls) or leaflets.

(xiii) Sori are protected by true (e.g., Marsilea) or false indusia (e.g., Adiantum, Pteris).

(xiv) The sporangial development may be leptosporangiate (e.g., Osmunda) or eusporangiate type e.g., Ophioglossum).

(xv) The sporangia in most cases have a distinct annulus and stomium.

(xvi) Members may be homosporous (e.g., Pteris, Adiantum etc.) or heterosporous (e.g., Marsilea, Regnellidium, Azolla, Salvinia etc.)

(xvii) Spores on germination form autotrophic prothalli (gametophyte).

(xviii) Antheridia and archegonia are partially or completely embedded in the gametophyte.

(xix) Embryo may or may not have suspensor.