This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Aquatic plants, or if terrestrial usually on moist ground, the leaves in a basal rosette, or borne along floating stems, or more or less root-like, or wanting. Inflorescence scapose. Flowers solitary or racemose, perfect, irregular. Calyx inferior, 2-5-lobed or parted, persistent. Corolla hypogynous, gamopetalous, 2-lipped, the upper lip entire or 2-lobed, the lower lip entire or 3-lobed, usually with a nectariferous spur. Stamens 2, borne upon the base of the corolla; anther-sacs confluent into 1. Ovary superior, usually subglobose, 1-celled; placenta sub-globose, central, free; ovules 2 or more, usually very numerous; style short or obsolete; stigma 2-lipped, the anterior lip larger, lamelliform. Fruit a capsule, bursting irregularly, or dehiscent by valves. Seeds variously appendaged or sculptured; embryo in the axis, often imperfectly developed; endosperm none.
About 16 genera and 300 species, of world-wide distribution. Scapes without bracts or scales, 1-flowered; leaves in a basal rosette.
Scapes with one or more bracts, with or without scales; leaves usually alternate, often dissected or root-like and bladder-bearing. Bracts at the base of the pedicels without bractlets; calyx not enclosing the fruit.
Branches verticillate, and verticillately or oppositely decompound; lateral lobes of lower lip of corolla saccate.
Branches alternate or none; lateral lobes of lower lip of corolla not saccate. Bracts, and scales if present, flat, basally attached; aquatic.
Bract solitary, tubular, surrounding the scape; scales none.
Bracts and scales peltate; terrestrial.
Bracts at the base of the pedicels accompanied by a pair of bractlets; calyx enclosing the fruit; terrestrial.