Rhododendron arboreum of the family Ericaceae represents one of the ancient tree species of the genus showing extreme disjunction in the Indian subcontinent. It occurs as two subspecies: ssp. arboreum in temperate forests of north-eastern India and ssp. nilagiricum in the tropical Western Ghats of southern India, with no distribution in the intervening plains.
The following biogeographical theories explain distribution of flora and fauna in the Indian subcontinent:
A. Island biogeography theory – Mountains function as isolated islands, promoting speciation.
B. Satpura Hypothesis – Species migrated between the Himalayas and the Western Ghats along a cooler, wetter corridor formed by the Satpura mountain ranges during glacial periods.
C. Noah’s Ark / ‘Out of India’ hypothesis – The Indian subcontinent, as a remnant of Gondwana, acted as an isolated “ark” giving rise to some modern plant and mammalian groups.
Which one of the combinations of biogeographical models explains the distribution of R. arboreum?

Correct option is C

Correct Answer:
(c) A and B only
Explanation:
The disjunct distribution of R. arboreum between the Himalayas and Western Ghats can be explained by the Satpura Hypothesis (B), which proposes a former continuous cooler and wetter corridor enabling migration during glacial periods.
Subsequent climatic warming caused extinction in the central plains, leaving isolated populations.
Island biogeography theory (A) further explains divergence into subspecies due to long-term isolation of montane “islands.”
Information Booster :
· Disjunct distributions often reflect historical climatic and geological events.
· Mountain ranges can act as refugia during adverse climatic phases.
· The Satpura corridor is a classic explanation for Himalayan–Western Ghats affinities.
· Isolation promotes subspeciation and local adaptation.
Additional Information (Incorrect Options):
Option A alone / A and C: The Noah’s Ark hypothesis explains deep Gondwanan origins, not this specific Himalayan–Western Ghats disjunction.
Option B and C: Noah’s Ark does not account for intervening extinction and subspecies differentiation.
Hence, A and B together best explain the observed distribution pattern.