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 .