Costoluto Genovese The fluted, old Italian favorite that has been around since the early 19th century. Fruit is rather flattened and quite attractive with its deep ribbing. This variety is a standard in Italy for both fresh eating and preserving, and known for its intensely flavorful, deep red flesh. They were also one of the varieties planted at Thomas Jefferson’s home in Monticello in 1809.
Costoluto Fiorentino Heavily ribbed (costoluta) flat Italian heirloom beefsteak type from Florence. Red, 12-16 ounces slightly flattened fruit. Outstanding taste. Large, vigorous, indeterminate plant with good production. Similar to Costoluto Genovese but slightly flatter and higher-yielding.
Costoluto refers to the distinct flattened, heavily-ribbed shape of various Italian heirlooms. Both of these tomatoes are shaped like this. some of my customers don’t like the ribbing but I think it is pretty and the taste is good. There is a reason these are heirlooms!
Both these pics are from my garden the year that I grew them.
Notes From The Tomato Lady 
It is amusing how these get around, and that tomatoes of Italian descent are more popular among those who are not of Italian descent. My ancestors preferred varieties that were developed in America, probably because they were commonly available.