Yellow Mushroom - Leucocoprinus birnbaumii
I think that’s what it’s called after searching about yellow mushroom on the Internet.

I was shocked to see those yellow heads in my plant pot after a hot and rainy day. I think this is what Malay proverb said about cendawan tumbuh selepas hujan - how fast mushroom sprouts after a rainy day. One day there are none, the next day one pops after another.
It’s probably poisonous so since mushroom grows by disseminating spores, I took them out from the pot and yet after a few days I saw a whole new bunch popped up in the same plant pot.
On my third attempt, I managed to evade their growth and hopefully I won’t get to see them again. I know they might be harmless for the plant, but still having something else sharing the soil of my precious flowering plant seems like a pest or weed to me..heh!

June 24th, 2008 at 8:52 pm
I found some little yellow shroomies too…Were yours growing in a pot with a “money tree” palm?
Interesting
Rob Windsor ONtario
July 23rd, 2008 at 3:16 am
IS IT ON A RUBBER PLANT CUZ THATS THE SAME FOR MINE
August 22nd, 2008 at 1:16 pm
It seems to be growing in any pot that gets the rain and sunshine, even in my Chrysanthemum pot..huhu
August 27th, 2008 at 12:55 am
It is a leucocoprinus birmaumii
September 3rd, 2008 at 9:41 pm
I have a rubber plant too, and it grew in there after the hurricane bands that we just had. It grew to the picture, and then all of a sudden in minutes, I looked back over, and it grew to a head! I was shocked!!
April 12th, 2009 at 3:51 am
Mushroom growth is so random… My garden goes years without ever seeing them, and then all of sudden — wham! They are everywhere for a couple of weeks. Still haven’t figured it out…
July 13th, 2009 at 10:47 pm
does anyone know if they can contaminate the surrounding plants? They are growing in my potted herb garden.
August 5th, 2009 at 12:36 am
Found the same thing in our “money tree” pot this morning. And oddly enough, we’re also in Windsor, Ontario like Rob above.
August 31st, 2009 at 5:31 pm
i saw this too is it poison
September 1st, 2009 at 4:58 am
having mushroom in you soil can be a good thing, mycellum running
September 3rd, 2009 at 11:20 pm
Leucocoprinus birnbaumii is harmless to you, your pets, and your plants as long as it isn’t ingested. The first time I saw them they popped up in my “money tree” as well (very interesting!) - In Manitoba a couple years ago. I really like how they look and I have been trying for a long time to harvest them and figure out their growth patterns with little luck.
September 8th, 2009 at 10:53 pm
yellow mushroom like picture growing with meyer lemon planted after hurricane IKE, GALVESTON 9/13/08
September 16th, 2009 at 8:41 am
I found one in in my pot with a cactus. Was shocked. Now that I know they are harmless I feel much better. I don’t know if this is useful to anyone but the soil in the pot was yellow for weeks so I thought it had mold from too much watering, was amazed to find a yellow mushroom sticking out of it today.