Golden rod, Aaron’s rod
This is a compact dwarfish variety of solidago which grows to around 12-15in tall with a greater spread. Solidago have a bad reputation for incurring mildew infections but this one is mildew free.
It is a perennial with wrinkled leaves which produces yellow-stalked bright yellow flower heads in conical panicles in late summer and early autumn.
All solidago like to be grown in full sun in hot dry conditions. They dislike being waterlogged in damp soil which is often the cause of the mildew attack.
These plants, if allowed to self-seed, can be a bit invasive but, in a less formal border, this may well not matter too much. It is very easy to lift and divide clumps when you cut down the old dead growth at the end of autumn as winter approaches or in a spring tidy up.