Hi Marthamc.
Your plant is botanically known as Syngonium. There are many common names with Arrowhead being the most common. There are several different species of this plant with different shaped leaves.
http://aggie-horticulture.tamu.edu/i...Syngonium.html
http://www.bachmans.com/tipsheets/in...wheadPlant.cfm
http://images.google.com/images?hl=e...-8&sa=N&tab=wi
This plant can be toxic if ingested.
http://www.ces.ncsu.edu/depts/hort/c...on/Syngopo.htm
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.