Apium graveolens var. secalinum Alef.
Chinese celery or leaf celery.
Thinner and leafier than what you may call 'regular' celery, Chinese celery is curved into round, hollow stalks. Frequently used and sold along with 蒜苗 (Mand: suàn miáo; Cant: syun3 miu4) above, this is known in Chinese as 芹菜 (Mand: qín cài; Cant: kan4 coi3).
It is used extensively in hot pots, but also simply stir fried with the leaves as a side dish. Here in Guangxi, a popular dish is Chinese celery with day lily, chilli and cashew nuts.
We also get regular celery which is 西芹 (Mand: xī qín; Cant: sai1 kan4), meaning 'western celery'. It is less popular.