Hydrophylloideae is a subfamily of the plant family Boraginaceae. Its taxonomic position is somewhat uncertain. Traditionally, and under the Cronquist system, the taxon was given family rank under the name Hydrophyllaceae, and treated as part of the order Solanales. More recent systems have recognised a close relationship to the borage family, Boraginaceae, initially by placing Hydrophyllaceae and Boraginaceae together in an order Boraginales, and in the 2016 APG IV system by including Hydrophyllaceae in Boraginaceae. However, the placement and circumscription of Boraginaceae is still uncertain. Some sources now split off Hydrophyllaceae again (together with Namaceae).

Plants in this subfamily may be annual or perennial herbs or shrubs, with either a prostrate or an erect stem. Most have a taproot. The flowers are bisexual, and normally radial, with 5 petals and 5 stamens. About 20 genera, containing around 300 species, are recognised; many of them are native to the western United States.

The subfamily takes its name from the genus Hydrophyllum (waterleaf). Members include Emmenanthe (whispering bells), Nemophila (baby blue eyes) and Phacelia (scorpionweed).

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