I share Joanie's attitude that, in fact, there is a lot of evidence that the Japanese do speak of bonsai as an art form. Many early publications speak of bonsai 'art'. (I do realize that the translator has some latitude in how words and concepts are translated.)
Bijutsu Bonsai Zu (
Artistic Bonsai in Painting / Catalog of Bonsai Art), 1881
Ushimaro, Sawada
Bonsai Geijyutsu (
The Fine Art of Bonsai); 1934.
Yuji Yoshimura The Art of Bonsai 1957
Kyuzo Murata Bonsai: Miniature potted trees 1964
"Bonsai of the best kind can be fully appreciated, much as painting or sculpture, for their elegance as...art"
Norio Kobayashi Bonsai-Miniature potted trees 1950
"In its broad sense a bonsai is no doubt a kind of potted plant, but it definitely differs from the latter in being a work of art, a fact which is universally admitted"
He goes on to describe the early (1934) Ueno exhibitions at the Art Gallery in Ueno park, ultimately known as the Kokufu Bonsai Exhibitions, which today are held at the prestigious
Tokyo Metropolitan Art Museum. Here's a recent page from
Tokyo Art Beat which listed the most recent Kokufu exhibition.
John