Which gymnosperm possesses a subterranean tuberous stem?

The male gametophyte of $Pinus$ is found to be

Top-shaped,multiciliate male gametes and the mature seed which bears only embryos with two cotyledons are characteristic features of which of the following?

Which of the following gymnospermic coralloid roots are associated with $N_{2}$-fixing cyanobacteria?

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?

What type of habitat characteristics do $Gymnosperms$ exhibit?