It’s easy enough to make most nouns possessive by adding an apostrophe and the letter “s:”
Tom’s fish tank has too much algae.
The school’s parking lot is small.
Don’t forget to stop and pick up a card for your grandmother’s birthday.
But possession gets tricky when the noun ends in the letter “s.” Do you add another one on top of it, or can that “s” do double duty?
Breathe a sigh of relief. Both choices are correct. Some styles, like Associate Press, suggest leaving that extra “s” off: “the lotus’ root.” Others suggest you include it: “the lotus’s root.” If you’re writing for a publication that adheres to a particular style, then follow that. If not, you decide.