Refers specifically to bok choy with white stalks, as opposed to チンゲンサイ (green-stalked varieties).
from Chinese
See also: チンゲンサイ
I stir-fried and ate bok choy.
Bok choy goes well with this soup.
Katakana spelling is standard for this loanword; the kanji form 白菜 is rarely used for this specific cultivar.
Kanji spelling is possible but strongly associated with はくさい (napa cabbage); using it for パクチョイ may cause confusion.
Borrowed from Chinese, likely via English 'bok choy' or 'pak choi'.