Which of the following plants is referred to as a living fossil?

Ginkgo biloba is widely recognized as a 'living fossil' because it is the sole surviving member of the Ginkgoaceae family, which dates back over 270 million years to the Permian period [t1][t5]. Charles Darwin first applied this term to the species due to its long geological record and the fact that it has remained virtually unchanged from its fossilized ancestors found in Triassic and Jurassic rocks [t1][t6]. While Cycas is also sometimes associated with the term due to its ancient lineage [c3][t3], Ginkgo is the most definitive example in botanical literature because it represents a monotypic group with no close living relatives [t1][t6]. Other options like Ephedra and Adiantum do not share this unique status of being a single surviving species of an otherwise extinct ancient order [t1][t9].

Sources

1. [1] https://adpcollege.ac.in/online/attendence/classnotes/files/1624875023.pdf
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 13: Plant Diversity of India > 13.6.10. Cycads > p. 203
3. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC10940627/