The Oxalis barrelieri contrasted very well in texture and colour with the dark drainage wall.
The weedy Tridax procumbens (common name: Coast Button) from the Asteraceae (Compositae) Family, shown in the 3rd and 4th photos, looked interesting and its flowers do provide nectar to some butterflies. A link is shown below for reference.
Even the wasp loved the Melastoma malabathricum (common name: Sendudok, Singapore Rhododendron) shown in the 5th to 8th photos and flit from flower to flower to collect nectar.