​Individuals belonging to the fossil genera Calamites are considered to be upright arborescent plants. They were characterized by stems which mostly arose from subterranean rhizomes. The cross sections of young stems showed the presence of a central pith canal and collateral vascular bundles with carinal canals. To which of the following extant genera is this plant most similar?​

Correct option is C

Explanation -

Calamites (extinct):
 They belonged to the Sphenopsida group (same as Equisetum). These were arborescent (tree-like) plants from the Carboniferous period.
They were characterized by - Hollow stems, Nodes and internodes, Rhizome-based branching , Collaterally arranged vascular bundles with carinal canals (i.e., water-conducting tissues surrounding a central canal).

Equisetum (horsetail):
The only living genus of Sphenopsids. They shares the following traits with Calamites - Hollow jointed stems, presence of nodes/internodes, carinal canals in vascular system, rhizomatous (underground stem system).
Thus, Equisetum is the closest living relative and most similar in morphology.

Incorrect Options-
Psilotum – Primitive vascular plant, but lacks true roots and leaves; no hollow stems or carinal canals.
Selaginella – A lycophyte with microphylls; unrelated structure.
Rhynia – Very primitive vascular plant (from Silurian/Devonian); does not have Calamites-like anatomy.


Final Answer - Option c - Equisetum​