Did ancient Romans reach America?

Did the ancient Romans reach the America? Let's analyze this possibility.
This could be possible for the following reasons:
• Knowledge of the spherical shape of Earth
• Romans had ships that were able to do that kind of travel
• We have found evidences of America endemic plants in the ancient roman world
• We have found Roman objects in America

The spherical shape of Earth 
Many philosophers, like Cicero, Plinius and Seneca, knew that the shape of the Earth was spherical and rotating around the Sun. They had precise sky charts, used also as a naval map. So, they was sure that it would be possible to travel to Indian east coast going to the West.

Ships
Roman ships were equipped to be able to afford a journey like that. In fact, the ship hull was covered by lead to protect the wood from the marine bio organisms. The sails were made to be able to sail also with headwind. The navigation it was easier thanks to an old type of compass, made with a natural magnetic rock.

America endemic plants in the roman empire
In the roman empire there were found evidences of America endemic plants, like corn, pineapple and sunflower. But it is not clear if those plants were traded directly by Romans or with the help of someone else.

Roman objects found in America 
In Canada, in the Oak Island, archeologists found some ancient roman objects such as a sword, a shield and a whistle. All this staff was evaluated authentic, and especially the sword was analysed accurately and authenticated by the Naples Museum, in Italy. But there are two problems to be solved: was this a direct trade between Romans and Americans? How to be sure that none have brought in modern times this objects from Europe to America? For now there are no answers.
There were found also some underwater tombs in Oak island. The Americans did not use tombs for their dead bodys, so the tombs have to be built by someone else. Another time, we are not able to know if these tombs are Romans or not.
The history channel archeologists and scientists think to have found what remains of an ancient roman ship near Oak Island. The evidences are not kept out from the water yet, to be analysed. If this discovery will be confirmed, this could be the evidence of the roman presence in America.

Personal thoughts
I think that there was for sure a trade between Europe and America, but we are not able to understand how it worked. In fact it is not clear if there was a direct trade between Romans and Americans or not. Despite it is sure that the roman ships were able to afford this kind of journey, the presence of romans in America it is not sure. Only other researches could prove that Romans reached America.

Bibliography
“Quando i romani andavano in America” book by Elio Cadelo
 Research of Professor James P. Scherz University of Wisconsin-Madison
Research of Professor Jovan Hutton Pulitzer for History Channel