I'd go with both Spot and Knowledge (nature) alternatives. The damage from this thing is pretty nasty, so maybe DC 20 to 25?
Changing "plant" to "fungus" is fine.
Shall we say DC 20 skill checks, for the sake of argument?
DC 15 for the Fort saves, like Yellow Mold?
Give it CR5, halfway between Green Slime and Yellow Mold?
Finally, I'm not sure about using a touch attack for the rhizome pod, but will leave that in for the time being. I'd certainly modify it to affect a 5 foot radius, though.
Putting that together...
Lure Lichen (CR 5)
A lure lichen is a deadly subterranean fungus that resembles a female humanoid with pale white hair and a similarly-colored gown. To distinguish a lure lichen from a sleeping woman requires a DC 20 Spot check or a DC 20 Knowledge (nature) check.
If a lure lichen is touched by a living creature it explodes in a 10 ft. radius cloud of poisonous spores (Fort DC 15). These spores do 1d6 Con damage as initial damage, as secondary damage they do 1d6 Con damage and infect the victim with a spore infestation. Lure lichen spore infestation is a disease (Fort DC 15) that does 1d6 Constitution damage per day. The corpse of any creature that dies while affected by a spore infestation will sprout a new lure lichen. Creatures immune to poison or disease are unaffected by the spores, and any bonuses to resist disease or poison apply to all saving throws against the spores. A
neutralize poison spell will prevent the poison damage or spore infestation, while a
remove disease spell will cure a creature of spore infestation.
In addition, the main body of the plant is surrounded by rhizomes out to a 20 ft radius. If a creature enters this radius, a rhizome will reflexively fling an immature spore pod at the creature as a ranged touch attack with attack bonus of +5. If the pod misses its target determine which square it hits as if it were a grenade-like missile. The spore pod bursts wherever it hits, creating a 5 foot radius cloud of immature spores. All creatures within the cloud must succeed at a DC 15 Fortitude save or suffer 1d6 Con damage.