Can you help me identify this plant? It has palmate leaves with 12 or more leaflets and flower spikes with whorled purple flowers.
These are called lupins (in Britain) or lupines (in the US). They are widely found as a wildflower, but there are many cultivated varieties, of which the most common I've seen are the Russell hybrids.
They are short-lived herbaceous perennials that flower from late spring to mid-summer depending on the warmth of the climate. They can be very susceptible to powdery mildew. They set seed easily, so even though they don't live for many years, they can form a self-sustaining colony. They also hybridize readily, so unless you get seed or plants from a controlled source, you won't know the exact flower color or shape until bloom.