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Which tissues from the mother and embryo form the placenta?

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A series of medical illustrations showing the stages of childbirth: the baby's position at the onset of labor, flexion, internal rotation of the head, extension, external rotation of the head, and the uterus immediately after birth with the placenta and umbilical cord. — birth Sequential changes in the position of the child during labour.

The placenta is a complex organ formed through the interaction of both maternal and embryonic tissues. Its development involves the following components:1

Maternal Component: The maternal part of the mature placenta is known as the decidua basalis. This structure is derived from the endometrium—the lining of the uterus—which undergoes changes to accommodate the encroaching conceptus.2
Embryonic Component: The fetal portion of the placenta is derived from the chorion, specifically the chorion frondosum. This component includes the branching chorionic villi and their associated fetal blood vessels, which extend into the maternal tissue to facilitate the exchange of nutrients, oxygen, and waste products.23

While these tissues are closely apposed to allow for physiological exchange, they remain distinct, separated by a placental barrier that prevents the direct mixing of maternal and fetal blood.31