un lămâi - masc sg = a lemon tree
and: doi lămâi - masc plural = two lemon trees :P
(the form for the tree does not change with the plural)
(I added a novel here: https://www.duolingo.com/comment/19682954)
Oh yeah I will avoid the subject. I'll rather try to talk about orange trees from now or maybe the weather :D
@ PaulMinden: how do you say it? :P
Sounds to me like "lamui".