In $Opuntia$,the spines are modifications of:

Leaves arise from which part of the plant?

In $1/2$ distichous phyllotaxy:

Leaves of dicotyledonous plants possess . . . . . . venation,while . . . . . . venation is the characteristic of most monocotyledons.

$A$ mature angiosperm that bears only one leaf is

Rachis is present in