Weird plant growing in my lemon tree pot
I've been taking care of this lemon tree for 2 years now with no fruits so far. I fertilize and water it as instructed online.
It's sitting in the balcony in my Dubai apartment. Temperatures here can get extremely hot during summer (up to 115F). I have two questions:
1- I've left this little plant grow at the base of my lemon tree. What is it ? It's not week is it ? I like how it looks but is it harmful to the lemon tree ?
2- Does my lemon tree look healthy ? i'm worried about the leaves curling but my guess is it's due to the extreme direct sun it had during the summertime (my balcony gets around 4 hours of direct sun rays).
It's my first post here and would really like some advice on it. I've attached some pics for my tree and the plant growing underneath it.