Prepared for B.Sc. Part II Botany Hons. by Prof. (Dr.) Manorma Kumari

Cycadeoidea (=Bennettites) Class Cycadopsida Order Bennettiatales Family Cycadeoideaceae Genus Cycadeoidea Cycadeoidea, is also called Bennettites by several European palaeobotanists. It has about 30 species. Majority of the species have been found as petrified trunks from America and a few from Europe and India from the upper Jurassic period to the upper Cretaceous of the Mesozoic era. Cycadeoidea etrusca was discovered from an Etruscan's tomb in 1860 as silcified trunk. Bennettites gibsonianus of lower Carboniferous was found in the form of silcified petrifactions from the Isle of Weight and Portland. Later studies of thin sections of their trunk reveals that Bennettites resembled Cycadeoidea in all respects and hence the two were declared to belong to the same genus. The name Cycadeoidea being older is retained. Morphological Features The genus Cycadeoidea had a short, branched or unbranched, stout, spherical to subspherical to irregular trunk that reached a diameter of about 50 cm.

Cycadeoidea dacotensis- Showing external feature

The surface of these petrified trunks was marked by several rhomboidal leaf bases. The height of the trunk rarely reaches a metre. In C. jenneyana it attained a height of 3 to 3.6 metres. The trunk was slow growing and profusely branched.

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It gives the effect of a bunch of pineapples. A compact crown of cycad-like large pinnately compound leaves was present at the apex of trunk that reached the length of 10 feet in some specimens. The trunk bears at its apex a compact crown of Cycad like large pinnately compound leaves that reached the length of 10 feet in some specimens. The leaflets had many parallel veins. Anatomical Structure Stem:

A cross section of the stem shows roughly a circular outline. The epidermis is not distinct due to presence of heavy armour of leaf bases. The cortex is wide and parenchymatous and possessed many mucilage canals and leaf traces. A ring of many conjoint collateral, open and endarch vascular bundles constituted the primary vasculature of the stem. A large parenchymatous pith is present. Medullary rays are present. The secondary wood encircles the primary xylem and consists of tracheids with scalariform and circular bordered pits. The tracheids appear rectangular in cross section. The secondary xylem and the secondary phloem are traversed by secondary medullary rays, which are uniseriate as well as biseriate. Cambium is district. A leaf trace developed single from the primary vascular strand and passes through broad ray of the secondary wood and on entering the cortex divides into several mesarch strands owing horse shoe-shaped at the place of its origin the leaf trace was C-shaped.

Cycadeoidea sp. T.S. of stem showing primary structure

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Leaf:

Transverse section through the pinnule shows a distinct upper and lower epidermal layer having thick walled cells. The mesophyll is distinguished into palisade parenchyma and spongy parenchyma. Each vascular bundle is surrounded by a distinct bundle sheath. Bundle sheath extensions are also clearly preserved.

Cycadeoidea sp. T.S. through the pinnule

Reproductive Structure The Bennettitalean reproductive organs are designated as 'flowers'. In Cycadeoidea the flowers are bisexual in majority of species and arise on short lateral stalks, singly in the axil of each leaf. In C. dertonii as many as 500 floral buds were found on a single plant and all of them were at the same stage of development. It is presumed that all of them opened simultaneously and the plant flowered only one in its lifetime. C. wielendii is unisexual. Structure of Flower The bisexual flower or strobilus consists of a central conical axis covered with megasporophylls (carpel), each bearing an ovule. The megasporophylls are interspersed with interseminal scales which were about same in number as the ovules. Around this is a whorl of 10-20 pinnately compound microsporophylls (stamens) and below this whorl, the stalk is surrounded by about one hundred bracts which were hairy and protective. Flowers in different species were of

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different size. In Cycadeoidea dartonii they attained a length of about 2 cm and a diameter of about 1.5 cm while in C. dacotensis each flower was about 8 cm long and 3 cm in diameter.

Cycadeoidea dacotensis: Bisexual flower

Microsporophyll or Androecium According to Wieland (1906, 1916), the androecium or pollen-bearing region consisted of about 20 innate, microsporophylls. These were somewhat fixed or united at the base bean-shaped pollen capsules. They were arranged in two rows on each pinna of the sporophyll. These microsporophylls remained folded around the gynoecium when young, but probably at maturity they expanded. Delevoryas (1963), however, opined that the microsporophylls never expanded. He further concluded that synangia-bearing structures, described as pinnae by Weiland (1906), were similar to the trabeculae. These trabeculae established a connection between outer and inner walls of the androecium. Pollen capsules or synangia were borne along these trabeculae.

Several (20-30) pollen sacs or microsporagia were present in a pollen capsule or synangium. The wall of a synangium consisted of outer palisade-like, thick-walled cells followed by thin-walled layer and then a tapetum. The pollen grains were oval in shape and measured upto 68 micron in length. Multicellular pollen grains in Cycadeoidea have been reported by Taylor (1973).

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Cycadeoidea sp. L.S. of Syangium Strobilus of Cycadeoidea sp. (vertical section)

Gynoecium The gynoecium consists of a conical or spherical receptacle that bears hundreds of the stalked ovules along with interseminal scales. Each ovule was about 1 mm in length. The integument of the ovule was fused with the nucellus, except at the apex (Harris, 1932). Each ovule has a pollen chamber and an external nucellar beak. Crepet and Delevoryas (1972) reported a linear tetrad in the nucellar region of Cycadeoidea. The ovule was orthotropous with a long micropylar beaks that extend beyond the pores in the surface plate formed by the union of distal flattened ends of interseminal scales. The fused tips of the interseminal scales form a type of external protective covering or pericarp surrounding the seeds.

The seed was somewhat elongated or oval in shape and possessed two cotyledons.

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