Extrasolar beings should bring extrasolar plants. Shouldnt they?

There are many threads out there claiming proof of human contact with extrasolar beings. (greys etc) I can understand that this may need to be kept quiet due to an inferiority complex hitting all humans and the breakdown of religios thoery leading to worldwide anarchy, this I understand.

However, the public search for extrasolar plants and bacteria continues. If we have made contact with humanoid beings then surely they would have supplied us with information about extrasolar plants or bacteria. If this information about plants and bacteria was made public and presented as if it was found by human scientists or astronauts then surely it would only reflect on them positively. Why hasnt this happened.

maybe aliens dont exist, maybe alien plants dont exist. What are your thoughts?

I'm a firm believer in panspermia on a bacterial level or the transfer of biochemical compounds across great distances of space, but without further proof I'll reserve comments on aliens.

We know for a fact that bacteria can survive the harsh environment of space so it's a real possibility that life has moved amongst the stars, transplanted and evolved on other worlds. Perhaps life on this world even started elsewhere and drifted here over thousands or millions of years.

As far as complete plants though, my experience in agriculture and greenhouses tells me that plants require very specific growing conditions. It would be difficult to take a cactus from one eco-system on our own world and expect it to survive even in another latitude or under different conditions.

Just slight variations in moisture, nutrients, or temperature, could mean the end of said plant. Though I won't deny that there are some very tenacious plant such as mosses and lichen that could make the transition with ease.
Perhaps lichen or bacteria will be the first things our species uses to start terraforming a planet like Mars.

It is VERY simple.

aliens aren't aliens, they are fallen angels, and earth is the only place with life.