The H'ylthri have had a few dealings with Earth.
They have also conspired against Iron Fist, as a hero of the humans of K'un-Lun. They captured him and created a fake Iron Fist out of plant materials. This fake Iron Fist was on Earth for some time before eventually being killed by Captain Hero (really the Super Skrull), in a plot devised by Master Khan.
They also gave the Plant-Man some of his technology to control plants.
They later tried to take over the Earth, using a spore weapon. That army was destroyed by Master Khan.
One of their leaders was Lord Sssesthugar.