subgroup

please say if it is possible that in Xerertic Calciargids subgroup we have xerertic prefix including xeric and vertic . so question is :

1- why these two words are not written as independent words for this subgroup for example can we say xeric vertic caciargid??

2- can we say vertic xeric calciargid ??
3- why xeric is said in the first and ertic is said later???

thanks to receive the answer soon