Mandayam Osuri Parthasarathy Iyengar (15 December 1886–10 December 1963) was a prominent Indian botanist and phycologist who researched the structure, cytology, reproduction and taxonomy of algae. He is known as the "father of Indian phycology" or "father of algology in India". He was the first President of Phycological Society of India. He primarily studied the Volvocales. Iyengar was an active sportsman and swimmer. He rescued two of his students from drowning in the Pamban in 1925. He was also a billiards champion in Madras. He died from cerebral thrombosis.