Marsh plants, with linear cylindrical leaves and inconspicuous flowers in spikes or racemes, appearing in early summer.
| 1a. Leaves all basal; flowers numerous in a spike-like raceme (Arrow Grass) [— 2.] | |
| 1b. Stem-leaves present; flowers in a loose bracted raceme (1-3 dm. high). | Scheuchzeria, Scheuchzeria palustris. |
| 2a. Fruit (usually to be seen at the base of the raceme) ovoid or oblong, rounded at the base | Arrow Grass, Triglochin maritima. |
| 2b. Fruit linear, narrowed at the base (1-5 dm. high) | Arrow Grass, Triglochin palustris. |
ALISMACEAE, the Water Plantain Family
Marsh plants, with scape-like stems; flowers with 3 green sepals, 3 white petals, 6 or more stamens, and several separate pistils.
| 1a. Ovaries in a ring; flowers in panicles (2-8 dm. high, summer) | Water Plantain, Alisma Plantago-aquatica. |
| 1b. Ovaries in a head; flowers in racemes or umbels [— 2.] | |
| 2a. Flowers all perfect, in a single umbel of 2-8 flowers; stamens 9 (leaves lanceolate; 15 cm. high or less; summer) | Dwarf Water Plantain, Echinodorus tenellus. |
| 2b. Flowers in a raceme of 3-flowered whorls, the lower pistillate, the upper staminate; stamens usually more than nine (1-10 dm. high, summer) (Arrow-head) [— 3.] | |
| 3a. Leaves ovate to linear, not sagittate at base [— 4.] | |
| 3b. Leaves broad or narrow, sagittate at base [— 5.] | |
| 4a. Pistillate (basal) flowers sessile or nearly so (2-8 dm. high, summer) | Arrow-head, Sagittaria heterophylla. |
| 4b. Pistillate flowers with obvious pedicels | Arrow-head, Sagittaria graminea. |
| 5a. Basal lobes of the leaf conspicuous, triangular, almost or quite as long as the terminal portion [— 6.] | |
| 5b. Basal lobes small, short, linear [— 4b.] | |
| 6a. Beak of the achene very short and erect; rare species | Arrow-head, Sagittaria arifolia. |
| 6b. Beak of the achene sharp, incurved at right angles to the body; common species | Arrow-head, Sagittaria latifolia. |
HYDROCHARITACEAE, the Frog's Bit Family
Submerged aquatics, with inconspicuous flowers in summer.
| 1a. Leaves all from the base, 2 dm. long or more | Eel Grass, Vallisneria spiralis. |
| 1b. Leaves on the stem, 2 cm. long or less | Water-weed, Elodea canadensis. |