Short Answer.
Each plant or group of plants has some phylogenetic significance in relation to evolution: Cycas, one of the few living members of gymnosperms is called the 'relic of the past'. Can you establish a phylogenetic relationship of Cycas with any other group of plants that justifies the above statement?
Cycas is considered a 'living fossil' because it is the only living species in the family Cycadaceae. All other species of this family are now extinct. This plant is often considered as the plant of the Old World; which means it is found only at those places which can be associated with some of the oldest rocks in the world. Due to these reasons; it is called the 'relic of the past'. Moreover, the Cycas plant shows more resemblance to Pteridophytes than Gymnosperms. This shows the phylogenetic relationship between Pteridophytes and Gymnosperms.
Some of the characters of Cycas which indicate this are as follows :
- Seeds are shed when the embryo is still mature. In other gymnosperms; seeds are shed only when the embryo is mature.
- The megasporophylls appear like leaves.
- In spite of the presence of pollen tubes, male gametes are flagellate.
- The leaf base is persistent.
- It shows circinate ptyxis venation like the pteridophytes.