Arctium Lappa vs Arctium Minus: Are these medicinally-interchangeable species?

Hello everyone.
I really could you some help.
In the area where I live (somewhere in Greece) we have plenty of Arctium (Burdock) growing wild everywhere.
I recognized a lot of these wonderful plants a couple of months ago, and due to the fact that I wanted to use them medicinally, I tried to identify them.
Then I met the Arctium spp. Minus where it is almost the same with it's "big cousin", arctium lappa.
They both have heart-shaped leaves, they are white underneath, where the only difference is a few, tooth like leaves, in the basal rosette of the plant.
Unfortunately, I watched several tutorials on youtube; I double checked my guides. These two plants are really hard to distinguish which one is which. The only difference occurs only in the second year of the plant, where arctium lappa surpasses in size the "minus" one.
Unfortunately the part used (roots) must be collected on the first year of plants growth
Does anyone have any experience on this? How can I tell the difference between those two species? Are these two plants interchangeable medicinally?
Thank you for your time,
Daniel

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