It completely depends on what kind of euphorbia. There are more than 2000 different plants in that family, all of which range from annuals, perennials and biannuals. Garden centers will commonly call a member of the family simply "euphorbia" because not all of them have a common name (like the most famous member: poinsettias), which would mean that they are identified as the usually complicated botanical name. If you still have the tag that was in the pot when you bought it, it should tell you the botanical name.
which flower? cut or potted?
mushrooms growing is a sign of too much water and/or too much acidity in the soil. Cut back on the water and add horticultural lime.
Euphorbia haeleeleana was created in 1971.
Euphorbia herbstii was created in 1988.
Euphorbia albomarginata was created in 1857.
Euphorbia chamaesyce was created in 1753.
Euphorbia skottsbergii was created in 1936.
Euphorbia thulinii was created in 1992.
Euphorbia epithymoides was created in 1762.
Euphorbia deppeana was created in 1860.
Euphorbia antisyphilitica was created in 1832.