One of the most luminous, vivid, hot pink colors in our garden comes from our four o'clock flowers (Mirabilis jalapa). Our plants were all started from seed collected in an abandoned garden area adjacent to our bank parking lot - I noticed the brilliant pink flowers and just had to get a close view of the plants. These tender perennials are also called marvel-of-Peru.
Although the smooth, dark green foliage wilts significantly with drought, the plants manage to survive with large, tuberous roots and will bloom profusely when conditions are favorable. The name comes from the fact that the flowers open late in the day and usually close up when it gets hot by about 10:00 a.m. the following morning. It took a year for the seedlings to get established but now the plants grow quickly in the spring, reaching a height of about 3 feet. Since the seeds germinate easily, the plants tend to grow in clumps and do best in shady areas. Given extra water during the hottest part of the summer, they begin blooming late in the season and really produce a lot of blossoms when temperatures drop a little in the fall.
I have seen a miniature version of our four o'clock growing near our house. This is probably wild four o'clock (Mirabilis nyctaginea), which is a native wildflower in our area. The whole plant is only about 1 foot tall and the blossoms are small and pale pink.