I've never been sure how to distinguish a rhododendron flower from an azalea. Consequently, when I brought up this photograph of a bloom taken in the park at Great Malvern I didn't know how to caption it. A quick internet search soon put me right: "On average, rhododendrons are larger shrubs than azalea plants, and they have larger leaves. Also, azalea flowers usually have five stamens, while the rhododendron flowers have ten. ... Finally, unlike rhododendrons, many azalea plants are deciduous." A quick count of the stamens shows this is almost certainly a rhododendron.
photo © T. Boughen Camera: Sony DSC-RX100