Cycas- Overview, Habit, Morphology and Anatomy
Cycas belongs to cycads. About 300 million years ago, cycads appeared in the Carboniferous period. Due to the significant evolutionary position between ferns and angiosperms, Cycads have some incredible unique characteristics.
Are cycads living fossils?
It is believed that it is not appropriate to call them living fossils since the living species are not reported to be older than 12 million years. Hence, they are said to be ancient.
Habit of Cycas
Cycas is an evergreen tree with a long life span and palm-like appearance.
Distribution of Cycas
Cycas is widely distributed in Asia. Here is a list of places that are home to various different Cycas species:
Malabar hills, Tamil Nadu and Odisha are home to C. circinalis
Bihar, Assam and Himalayas are home to C. pectinata
Andaman and Nicobar is home to C. rumphii
Morphology of Sporophyte of Cycas
To begin with, primary roots are tap root type and short-lived. They give rise to lateral roots. Specialised apogeotropic collaroid roots are formed as a result of modification of the upper part of this root system.
Collaroid roots are produced in clusters. Dichotomous branching is particularly observed in the collaroid roots. An algal zone is reported in the cortex which is inhabited blue-green algae like Anabaena and Nostoc. These roots are specifically termed so because of their coral-like appearance.
The young stem is tuberous but the mature stem is thick and unbranched.
The arrangement of leaves is spiral. Scale leaves are brown and protective in nature whereas foliage leaves are green
and hence, are photosynthetic. Leaflets are borne on the rachis.
Anatomy of Sporophyte of Cycas
To begin with, the epidermis of the stem comprises thin-walled cells. It is covered by the cuticle. Cortex comprises large parenchymatous cells along with mucilaginous canals and storage starch in cells. The endodermis is inconspicuous and so is the pericycle. The vascular bundles are conjoint, collateral and open in nature. Medullary rays separate the vascular bundles. Specialised spiral thickenings are observed in the case of tracheids of protoxylem and the metaxylem has marked scalariform thickenings. Pith is large and parenchymatous.
Angiosperm-like roots are seen in Cycas. The outermost layer Epiblema is followed by the cortex. A number of mucilage canals are observed in the cortex. The endodermis is single-layered with casparian thickenings on tangential walls of cells.
The metaxylem has scalariform and pitted thickenings whereas the protoxylem has tracheids with spiral thickening. To summarize, the secondary growth pattern is similar to that of dicot roots.
Stay tuned for the reproduction in Cycas in further articles.
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