mushroom
圥 centers on mushrooms as a type of fungus. The meaning is narrow and concrete, with no clear abstract extensions.
The historical origin of 圥 is uncertain. It combines 土 (earth) and 儿 (legs), but how this relates to 'mushroom' is unclear.
Picture 土 as the soil and 儿 as the stem and cap of a mushroom pushing up from the ground.
For ロク, imagine a mushroom growing on a log: log -> ロク, and the mushroom sprouts from the earth.