Cycas - Morphology of sporophyte

Cycas

Division      :         Cycadophyta

Class           :        Cycadopsida

Order           :        Cycadales

Family        :         Cycadaceae

Genus                   :        Cycas

Gymnosperms are plants which produce naked seeds i.e., plants which lack ovary and hence do not produce fruits. Cycas belongs to this group of plants.

The genus cycas is the most widely distributed genus of the order cycadales. There are about 20 species which grow in the wilderness in China, Japan, Australia, Africa, Nepal, Bangladesh, Burma and India. C. circinalis, C. pectinata, C. rumphii and C. beddomei, are found in the wilderness in India. C. revoluta is grown in gardens in India.

Species of Cycas are of considerable economic importance. Starch is extracted from several species of cycas. Young succulent leaves are used as vegetable in some parts of  India. Several species of cycas are of medicinal value. The juice of young leaves of C. circinalis is used as a remedy for stomach disorders, flatulence, blood vomiting and skin diseases. The decoction of young seeds of this species is purgative and emetic. A tincture prepared from the seeds of C. revoluta is used to relieve headache, giddiness and sore throat.

Morphology of sporophyte: Cycas is an evergreen slow-growing palm-like small tree with an average height of 1.5 to 3 meters (fig). It is commonly found in dry habitats. It also grows well in gardens of tropical countries Fig. 1.56. Cycas - Habit including India. The sporophyte is differentiated into roots, stem, and leaves.

Roots: There are two types of roots in cycas 1) Normal roots, 2) Negatively geotropic roots called coralloid roots.

Normal roots: The long-lived primary root is usually thick and short but the lateral roots are thin and long. These roots are positively geotropic. Their main functions are anchorage and absorption of water and mineral nutrients.

Coralloid roots: These roots are n e g a t i v e l y geotropic and grow on the surface of the soil. They are dichotomously branched and appear as coralline masses (fig). A specific algal zone with colonies of Anabaena or other blue green algae is present in the cortex of these roots. The algal cells may help in N2 fixation. These roots respire through special openings called lenticels.

Stem: The young stem is tuberous and subterranean and its apical part is covered with brown scale leaves. The old stem is thick, columnar and woody. It is covered with persistent and woody leaf bases. The stem is usually unbranched, but sometimes due to shoot tip injury, the stem branches dichotomously.

Leaves: Cycas has dimorphic leaves namely 1) Foliage or assimilatory leaves and 2) Scale leaves.

1.Foliage or assimilatory leaves

Large, pinnately compound (fig) foliage leaves form a crown at the top of the stem. Each leaf has 80-100 pairs of leaflets. They are arranged on both sides of the rachis in opposite or alternate manner. The leaflets are sessile, elongated and ovate or lanceolate with flat or revolute margins. The tip of each leaflet is acute or spiny. Each leaflet has a single midvein. Lateral veins are absent.

The rachis of a very young leaf is circinate with circinately coiled leaflets like those of ferns.

2.Scale leaves

These are small, rough, dry and triangular in shape. They protect the shoot apex and other aerial parts. They do not produce starch by photosynthesis. The foliage and scale leaves are arranged in close alternate whorls at the apex of the stem.