Fimbristylis thomsonii Boeckeler, Linnaea 37: 37 1871. (syn: Iria thomsonii (Boeckeler) Kuntze);
Assam; Bangladesh; China South-Central; China Southeast; East Himalaya; Hainan;
Laos; Malaya; Myanmar; Nansei-shoto; Philippines; Sumatera; Taiwan; Thailand;
Vietnam as per Catalogue of Life;
SK1419 07 Sep 2018 : 8 posts by 4 authors. Attachments (6) – around 600 kb each.
Location: Victoria Peak, Hong Kong
Date: 12 August 2018
Elevation: 1300 ft.
Habit : Wild
Juncus sp. ??
your guess is on track
This is Juncus, but not easy to confirm the species.
This should be Fimbristylis thomsonii.