SALVINIALES

ORDER SALVINIALES

Spores alongwith cytoplasm of degenerating tapetal cells form small units called massulae . 

Azolla 

Azolla is also known as mosquito fern or mosquito net .They are found on the surface of permanent pools . Azolla imparts characteristic reddish colour to the pond . 

          Sporophyte is made up of branched rhizome , adventitious root and leaves .The mature rhizome has ectopholic siphonostele . leaves are minutes ( up to .5 m ) . They grow in two alternating rows on the dorsal surface of rhizome . Each leaf is divided into two equal lobes - 

1. Aerial lobe - upper , green , thick , photosynthetic , obliquely placed , touches water only on the edges , has large cavity containing anabaena azollae . 

2. Submerged lobe - lower , thin , colourless , absorbs water . 

          Upper epidermis of leaf is covered a tuft of hair which traps air and protects leaves from wetting . 

          Vegetative reproduction occurs by fragmentation . Two types of sporocarps - microsporocarps and megasporocarps are fund in azolla . Each sporocarp is capable of bearing either microsporania or macrosporangia but during the development they get either of them . Megasporangium is always the first to be formed . If megasporangium degenerates then microsorangium is formed . Sporocarps are borne on the fertile lobe of  lowermost leaf of a lateral branch . True Indusium ( from stalk ) is present and surrounds the sporangium completely except opening . Azolla is heterosporous . 

         Large megspore ( 1 ) with surrounding degenerating cytoplasm of other megaspores ( 19 )  form a honeycomb like float corpuscle or massulae . It serves as swimming apparatus and provides buoyancy to the megaspore .  

         Microspores and cytoplasm of degenerating tapetal cells form float corpuscles or massulae . Each massulae has peripherally situated cytoplasmic strands called glochidia . This massulae attaches to the rugged surface of the megaspore with the help of glochidia . Both the mega and microsporocarps sink to the bottom of the pond . Massulae are set free after the death and decay of sporocarp wall . 

Salvinia 

Salvinia are free floating aquatic ferns . They are found in still waters of pond and lake . They lack roots . They have hairy branched rhizome .The node bears leaves and branches . Salvinia shows dimorphism of leaves . They have tow types of leaves - floating and submerged leaves . Upper epidermis of floating leaves have hair to trap air and to prevent from wetting . Submerged leaves are finely divided , boat shaped and act as balancers . 

         Salvinia is heretosporous water fern . Each sporocarp represents a sorus .  All sporocarps are strictly monosporangiates  ie. they bear either microsporangia or macrosorangia . All other features of sporophytes and gamatophytes are similar to azolla . 

TAXALES

ORDER TAXALES

The order taxales includes single family Taxaceae . 

Taxus

Taxus is commonly known as yew .Taxus baccata is common species in India . It is an evergreen , densely branched , medium sized tree . It has tap root .Taxales is charaterised by the absence of resin canals in the aerial parts, they are restricted only to roots .The stem is monopodial and profusely branched . The foliage leaves are linear to lanceolate , sharply pointed at apices that contain silica particles . They are spirally arranged but as the leaf bases are twisted they appear to be in two rows . The scale leaves are minute , membranous and arranged in opposite decussate manner . Both the roots and shoots of Taxus show secondary growth .Taxales is characterised by the presence of tertiary thickenings (as spiral bands ) and uniseriate pits . The wood of Taxus is pycnoxylic . 

         Taxus is dioecious and heterosporous species .They show eusporangiate type development of sporangium . Male cones or female flowers develop in the axil of leaves . Male cone has sterile bracts on basal portion and 6-14 microsporophylls at upper portion . Each microspoprophyll has 6-8 microsporangia . Microsporangia have many microspores .  Female flower has sterile bracts at basal portion and an unitegmic , orthotropous ovule or megasporangium at upper portion . A fleshy edible covering called aril encloses the ovule . Prothalial cells are not formed in Taxus .Tent pole is present in the female gametophyte in Taxus . Archegonial jacket is present around the archegonia . It provides nutrition to archegonia from endosperm . Pollination in Taxus is anemophilous . Taxus takes 2 month between pollination and fertilization . Taxus has non-endospermic seeds . Seed germination is epigeal . 

         The whole plant except aril is poisonous due to presence of alkaloid taxin , therefore Taxus is called death tree . The leaves of Taxus have ephedrine which are used in asthma , bronchitis and epilepsy . 

        

          

EPHEDRALES

ORDER EPHEDRALES / GNETALES

Ephedrales includes family ephedraceae . Family ephedraceae is monotypic and represented by Ephedra only . 

Ephedra

Ephedra foliata is only species found in India ( Punjab and Rajasthan ) . Ephedra is source of drug ephedrine . Aromatic beverage mormon tea is also brewed from the species of ephedra . Most species of ephedra are shrubs . They have tap root , Stem is profusely branched , jointed and differentiated into nodes and internodes . The number of branches is equal to the number of leaves present at the node . Due to the jointed nature of stem and whorled branches Ephedra is commonly known as jointed fir . It resembles equisetum . Leaves are minutes , scaly and sessile . Only stem shows secondary growth in ephedra . In the presence of vessels in the xylem ephedra resembles angiosperms but vessels have different origins . Ephedra vessels show size variation according to season . There is a plate like structure of lignified cells in the node called nodal diaphragm . Stem of ephedra easily breaks at node due to the presence of nodal diaphragm . 

       Ephedra are strictly dioecious . Cones ( male or female ) arise in whorls in the axil of leaves . Each male cone has many paired bracts ( perianths ) . Stamens ( male flower ) arise from between bracts of pairs . Each stamen has a stalk ( microsporangiophore ) and anther ( 2-8 microsporangia ) .Thus male cone of ephedra is comparable to inflorescence . Male gametophyte of ephedra shed at 5 celled stage . 

       Female cone is usually smaller than male cone . Each cone has 2-4 bract pairs . Most bract pairs are sterile , only two upper bracts have an ovule ( one for each ) . Ovules are orthotrpous and unitegmic . 

       Ephedra shows double fertilization like phenomenon ( fusion with egg and venter canal nucleus ) .Pollination is anemophilous . Fertilization in ephedra is siphonogamous . Ephedra shows embro sac polyembryony . Seed germinationn is epigeal .