The Bennettitales (Cycadeoidales) are a fossil group found from the Triassic to the lower Cretaceous, but were predominant in the Jurassic period of the Mesozoic era in South America, North America, India, and many other places, mainly in the southern hemisphere.
The members of this group were cycad-like plants. Recent investigations have shown that the Bennettitales are very distinct from the living cycads. Hence, Bennettitales have been considered an indipendent order (Arnold, 1947).
Characteristics of Bennettitales
- The sporophytes were short, tuberous, or columnar in form. Sometimes slender, branched trunks occurred.
- The occurrence of abundant membranous scales, thickly packed between the leaf bases.
- The stem was covered by an armour of persistent leaf bases.
- The stem anatomy was like that of cycads, i.e., with a thick cortex, a thin vascular cylinder, and a large pith. The vascular bundle was collateral and endarch. In leaves, the vascular bundle was mesarch like ferns.
- Wood was monoxylic.
- Leaf traces at the first endarch, near the vascular cylinder, soon become mesarch and straight.
- Leaves were large, pinnately compound, and spirally arranged, forming a crown at the apex of the stem like that of Cycas.
- The venation was unicostate and parallel.
- The stomata were syndetochilic.
- The reproductive organs were bisexual, borne terminally on short axiliary branches. Strobili were often termed flowers.
- Many inter-seminal scales were present on the ovule-containing receptacle.
- The ovule and seed were stalked.
- The seeds were without cupules.
- The flowers were surrounded by numerous hairy bracts that were developed from a conical, cylindrical, or dome-shaped receptacle.
- The male and female gametophytes have not been found.
- The microsporophylls, or pollen-bearing organs, were developed in whorls and may be pinnate (Cycadeoidea), entire (Williamsoniella), or fused (Williamsonia).
- The pollen grains were borne in bilocular synangium that may be sessile or stalked.
- The seeds with two cotyledons and were covered by two or three layers of testa.
Classification of Bennettitales
Arnold (1948) divided Bennettitales into two families:
- Williamsoniceae (e.g., Williamsonia, Williamsoniella)
- Cycadeoidaceae (e.g., Cycadeoidea)
Sporne (1965) classified it into following three families:
- Williamsoniceae (e.g., Williamsonia)
- Wielandiellaceae (e.g.,Williamsoniella)
- Cycadeoidaceae (e.g., Cycadeoidea)
