wide expanse (of flowers)
Used for a broad, visually striking spread of flowers, often in a natural setting. Less common than the group sense.
There was a flock of pigeons in the park.
A crowd of people had gathered in front of the station.
A wide expanse of rapeseed flowers bloomed on the hillside.
Compound of 一 (ひと, 'one') and 群れ (むれ, 'group, crowd'). The reading ひとむれ is a straightforward combination.