两个是同一种东西。只是叫法不同。 They are the same thing, just different names. 参考百度百科： reference: http://baike.baidu.com/link?url=sKsQ6Utj4phsNAj8-c80D9ZRe1YTk5SjRHM0I7V-XbUe0k1_sl7tpgn2YoFhRqkaAXhGUfH8O7jXKLSlBdSmVH_yJx9YgAdDBE-fRjPrhdtJwBsJ0x68kmbeXzlXGOEEZ3zghzqltdA_5pSTiXs1Ptpw4iQXuqfQTEzG4nsitLusvn54kQIKyvJTmyKwKG7v 第一行写道：同义词 西红柿一般指番茄（茄科茄属植物） In the first line, it says: they are synonymous, 西红柿 generally means 番茄 就像马铃薯和土豆一样，完全相同 It's like the relationship between "马铃薯"and "土豆", they are all potatoes.

3 characters vs 2 characters

西红柿=番茄=tomato

In Taiwan, we always say番茄, and usually called 西紅柿 in China.