Egyptian Starcluster is NOT what I have ever heard anyone ever call this plant. We've just called it Pentas. Say PENT-az. The full Latin name is Pentas lanceolata. It is a tender perennial(meaning it's frost tender) that grows about 4' tall here in SoCal. There are some short varieties sold in nurseries. My white one is a short one. But the other 3 are tall, bloom almost year round and the hummingbirds LOVE them! And they make good cut flowers for small bouquets as the stems are only about 6" until the next leaves and flowers. I grow mine in part shade with an eastern exposure. Morning sun is fine. But they might fry in all day sun inland. They do need some deadheading(cutting off spent flowers) to bloom more.
The pale pink one is my latest plant. I couldn't resist it at Roger's Gardens down in Newport Beach a few weeks ago. I want to collect all the colors. I think I'm only missing purple now. I used to have a short purple but lost it. And there are some reds and pinks that have a white eye.
Do you grow Pentas? They're easy!
Happy Gardening in the Dog Days of August!