1|Page Cordaitales The Cordaitales represent the most ancient order of the class Coniferopsida, which appeared in the Devonian. They were the only representatives of the Coniferopsida in that age. They were at their peak of development during the carboniferous period of the Palaeozoic era and were succeeded by the Ginkgoales and the Coniferales in the Mesozoic era. Classification The order has been divided into three families: (i) Cordaitaceae, (ii) Eristophytaceae and (iii) Poroxylaceae. The order is represented in India by 4 genera and 26 species. CORDAITACEAE External characters —The members of this family formed the world's first great forests towards the close of Lower Carboniferous. —It included tall trees (upto at least 30 meters in height) that grew in dense stands. —The stems attained a diameter of 65 centimeters or a little more. —The branching was lateral and confined only to the top of the tree. —The leaves appeared on the branches. They were— spirally arranged, petiolate, simple subulate, spathulate or grass like with entire margins and obtuse or acute apices. The venation was parallel. —The leaves showed considerable variation among the members of the family and were put under the type genus Cordaites. This name is now applied to the stem as well as to the whole plant. —Based on the differences among the leaves of various Cordaitaceae the genus Cordaites has been sub-divided into three sub-genera: 1. Eu-Cordaites 2. Dory-Cordaites 3. Poa Cordaites —The roots were named Ameylon. They arose from the base of the stem and were repeatedly branched. Dept of Bot/M.Sc. Sem-I (Bot)/ANC, Patna/Sushil ANATOMY Stem —The cordaitalean stems are Mesoxylon, Cordaites, Metacordaites, Parapitys, Coenoxylon, Mesopitys, Cordaicladus and Artisia. —In Cordaites the stem had a large cortex with sclerenchymatous patches scattered amid the parenchyma. The secretory sacs were also present. The pith was wide and extensive and peculiar in being discoid. The characteristic feature of the pith is the presence of large air chambers separated by diaphragms. The pith was transversely septate at the margins. The petrified material indicated that diaphragm was incomplete. —The primary xylem forms a narrow zone around the pith and consists of large number of endarch protoxylem. —In Mesoxylon the xylem in mesarch. —The stem genus Metacordaites had no air chambers on the pith and the xylem was endarch, whereas in Parapitys the xylem was mesarch. —In Coenoxylon and Mesopitys the pith had thick walled or sclerenchymatous patches distributed in the pith. Both has endarch primary xylem. The bundles were open. —As a result of secondary growth compact or pycnoxylic secondary wood is formed, that is, usually traversed by narrow or uniseriate vascular rays. —The tracheids were long and narrow. The vascular pitting was primarily restricted to the radial walls. The bordered pits were hexagonal in outline and occurred usually in uniseriate rows. Metaxylem also showed some scalariform pitting. It is believed that in Mesoxylon the leaf traces were mesarch, but most of the cauline bundles had endarch xylem. —The phloem is not well preserved. It showed sieve tubes and phloem parenchyma. Presence of phloem fibers is doubtful. 2|Page The leaf The cordaitean leaf traces were either single or double at their point of origin from the primary vasculature. In Cordaites the strands were endarch whereas in Mesoxylon they were mesarch. Root —The roots in Cordiatales (Ameylon) were usually triarch, exarch and protostelic. — —presence of periderm around the secondary cylinder. —Extensive secondary wood —Another root genus is Premnoxylon. It was —exarch with the number of xylem poles varying between two to seven or even greater —pith had sclerenchymatous patches and the —secondary xylem formed a distinct ring —The root cortex was divisible into an outer and an inner cortex. —Periderm present in the outer cortex. Leaves: The leaves showed xerophytic adaptations. —distinct epidermis on the upper and lower surfaces (bifacial). The epidermal cells were thick walled. —The sclerenchymatous hypodermis occurred in the form of distinct patches on both sides in C. angulostriatus whereas in C. rhobinervis it formed a continuous layer interrupted by distinct sclerenchymatous bundle sheath extensions. —Clear distinction into palisade and spongy parenchyma in C. lingulatus. —Vascular Bundles: Mesarch The bundles were surrounded by a distinct sclerenchymatous bundles sheath. —The stomata were arranged in distinct bands along the entire length of the leaf. —The guard cells were surrounded by 4-6 subsidiary cells. —Two polar subsidiary cells in every stoma abut on the ends of the guard cells. Dept of Bot/M.Sc. Sem-I (Bot)/ANC, Patna/Sushil Reproductive organs —The fructification of Cordaites is Cordatianthus (Cordaianthus). —The fructifications occur among the leaves on the stem. — Each fructification was borne on a vegetative shoot and consisted of an axis which bore spirally arranged bracts with axillary reproductive shoots/dwarf shoots/short shoots. Male strobilus/microsporangiate short shoot: —The three well studied forms include Cordaitanthus concinnus, C. penjonii and C. saportanus. —Each dwarf shoot had a central axis with a large number of spirally arranged and uni-nerved scales. —The scales at the proximal end- sterile whereas those near the apex or the distal ones-fertile —The scale possessed 4 (C. saportanus) or 6 (C. penjonii) or many microsporangia or pollen sacs. —Microsporangia: — elongate and finger like structures —each microsporangium separately vascularized. —The vascular strand that supplied the sporophylls were mesarch and forked dichotomously near their apices to send a branch to the base of each microsporangium. —The microsporangia had a single layered wall enclosing large number of pollen grains or the microspores(65 to 150 . in diameter). —The microspores had an equatorial bladder or an air cavity enclosed by the exine. This is the saccus. —The inner wall or the intine enclosed a central cavity which contained cellular remains of microgametophytes. —The cavity of the germinated microspore is occupied by a row of peripheral male prothallus cells and a row of central spermatogenous cells. —Each spermatogenous cell divided into two spermatozoids that were multiciliated. — These were liberated into archegonial chamber by the disintegration of the intervening nucellar tissue. —Pollen tubes have not been found. 3|Page —The pollen grains were trilete on the proximal surface. Female strobilus/megasporangiaqte strobilus or dwarf shoot: —The organization of the female stroblus is similar to that microsporangiate dwarf shoot. — They arise as lateral outgrowths from the inflorescence axis.. — Each strobilus had a central axis with spirally arranged appendages. —The basal or proximal appendages were sterile whereas the distal ones were fertile and bore one to three ovules terminally. —In Cordaitanthus pseudofluitans the distal fertile appendages/sporophylls were greatly elongated. They dichotomized one or more times and bore two to more terminal ovules. —Ovules were more or less pendulous, fattened and showed a tendency to be recurved towards the main axis. —The fertile appendages later grow more and project beyond the short shoot. —In C. zeilleri the dwarf shoot bore only four fertile appendages or sometimes only one. The megasporophylls were unbranched and bore only one terminal erect ovule. —The ovules were bilaterally symmetrical and were enclosed with in a single, but two parted integument that were completely free from the nucellus. — A distinct pollen chamber was found containing germinated pollen grains. The ovules appeared heart shaped from the broad side. —The single median bundles entered the sporophyll and divided into three just below the ovule. —The integument consists of two or three distinct layers of tissues (i) sarcotesta or the outer fleshy layer; (ii) sclerotesta or the middle stony layer; and (iii) endotesta or the inner narrow and fleshy layer. In Cardiocarpus spinatus the sarcotesta is fleshy, whereas the sclerotesta is hard and stony and is highly resistant to decay. — The nucellus, in the mature ovules, appears as a thin band of tissue surrounding the female gametophyte. Dept of Bot/M.Sc. Sem-I (Bot)/ANC, Patna/Sushil — The female gametophyte consists of a parenchymatous mass of cells with two archegonia towards the micropylar end. —The female gametophyte in most of the ovules encroaches upon the nucellus almost to the integument and also develops a characteristics endosperm beak which supports the nucellar beak and is called the tent pole as in Ginkgo biloba. —The archegonial neck opens into a distinct archegonial chamber which surrounds the tent pole. POROXYLACEAE This family is represented by a single genus Poroxylon whose seeds are put under the form genus Rhabdospermum. ERISTOPHYTACEAE It includes the form genera Eristophyton, Endoxylon and Bilingea.
