Yellow Alder

Turnera ulmifolia opens a fresh set of bright yellow flowers every morning and closes them by early afternoon, and it does that almost every day of the year in a warm climate. Nothing else at this size gives colour on that schedule.
It makes a soft, rounded bush of about a metre with serrated elm-like leaves, and it is used as a mass bedding shrub on hot, exposed sites where irrigation is limited.
Yellow Alder gives a daily flower cycle at low height on very little water, which makes it a workhorse of hot-climate mass bedding.