I think this statement needs clarifying
"........ "Whoever invents or discovers and asexually reproduces any
distinct and new variety of plant, including cultivated sports, mutants,
hybrids, and newly found seedlings, other than a tuber propagated plant or
plant found in an uncultivated state, may obtain a plant patent therefore
..........."

This refers to plants propagated by producing a lot of individual tubers,
such as Potatoes and not to plants that can be propagated from cuttings and
then produce a tuber such as Dahlias.
Don't be confused by Canna Lilies, apart from not being Lilies also don't
produce a "Tuber" despite this description being used for their fleshy root
structure, more correctly it is a rhizome.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk