Asari mating, Protheans and Ardat-Yakshi

Hmm.  Perhaps the asari are like Earth's anglerfish, in that there are "males" that embed themselves into a female's body, re-absorb almost all of their internal organs, and function as sperm repositories for the female to use at her leisure.  If you encountered a free-living asari male, at first glance you wouldn't even recognize it as being of the same species as the females, in the same way you wouldn't guess that a caterpillar and a butterfly are the same species.  If the game developers had been bold enough, we might have had a reveal that each asari "hair tentacle" was actually a male asari parasitically attached to the female asari's head.

More seriously, the asari are one of the biggest examples of Artistic License: Biology in Mass Effect 1, given that the meiotic recombination of genes was one of the major evolutionary advances that led to the success of us multi-cell eukaryotes.  Multicellular eukaryotes with a single sex tend to be hermaphroditic, e.g. slugs and snails, rather than exclusively female -- and the few obligate parthenogens out there, such as whiptail lizards, tend to show signs of evolutionary stagnation (low diversity, decreased viability over time due to deleterious mutations accumulating across generations).  You can get *some* of that back with recombination -- the games do mention "randomized genetic material" -- but it's not as powerful as combining two lineages.