Which of the following represent the maximum number of species among global biodiversity?

$A$ : India falls under the Oriental realm out of the major biogeographical realms.
$R$ : The world is divided into six biogeographical realms.

The variation shown by the medicinal plant $Rauwolfia \text{ } vomitoria$ growing in different Himalayan ranges represents:

Definition / Explanation: $\beta$-diversity.

Tropical regions show the greatest level of species richness because:
$A$. Tropical latitudes have remained relatively undisturbed for millions of years,hence more time was available for species diversification.
$B$. Tropical environments are more seasonal.
$C$. More solar energy is available in the tropics.
$D$. Constant environments promote niche specialization.
$E$. Tropical environments are constant and predictable.
Choose the correct answer from the options given below.

In which regions does the plant $Rauwolfia \text{ vomitoria}$ show genetic diversity?