I grew this groundcover Lobelia chinensis (common name: Chinese Creeping Lobelia; Family: Campanulaceae) at various parts of HortPark extensively but most of the beds were gradually replaced by other plants.
This patch at the tail end of the Carpark Garden remains. It seems to prefer full sun conditions and wet or moist soils. The flowers are small, purplish and have 5 petals. A link on this plant is attached below: