Naoki is more or less correct. It means green stem, but the indication is there is no other pigmentation. If there is red pigmentation, it is referred Doro Jiku/泥軸 (muddy stem). Aojiku characteristic seems fairly important for Japanese, and you will see the term being used for other (
CLASSIC) plants such as
Hepatica. There are other variation such as Kuro Jiku/黒軸 (black stem) and Aka Jiku/赤軸 (red or reddish stem).
*国豆弁* 赤軸*心 : ＤＲＥＡ* ＧＲＡＳＳＥＳ
Interestingly, there is even a Wiki entry on this:
富貴* - Wikipedia
Hybrid Mode
