I think having some fairly complex life forms in world's biosphere being asexual for a long time would add a lot in terms of mystique and spur lore engagement. I was intrigued by some discussion on this article concerning the evolution of sexual reproduction. One segment in particular:
Furthermore, even though asexual lineages do arise, they rarely persist for long periods of evolutionary time. Among flowering plants, for example, predominantly asexual lineages have arisen over 300 times, yet none of these lineages is very old.
It seems that currently, we see little to no examples in nature for asexual lineages to persist for long periods of time (in terms of geological/evolutionary time scales). While there are several facets to this question, I will narrow the scope to the issue of diversity/lack-there-of.
The Red Queen hypothesis asserts that when a species' genomic make-up remains unchanged for too long, it imposes a extinction risk factor on itself -- the rest of the biological world is evolving and eventually some mutations elevate competitive norms.
Below is a diagram that illustrates the concept (as well as the adversity an asexual lineages in trees, plants, more complex life)
How can an asexual lineage of trees/flowers/similarly complex life forms continue to reproduce and stay "competitive" for millions of years?
- Microbes are out of scope
- Trying to avoid too many double-digit-sigma events (not asking them to be mass-extinction proof or anything, but also not assuming they can have the perfect random mutation at each juncture)