About 5 species occur in Michigan, of which the commonest is =Bur-reed, Sparganium eurycarpum.= NAJADACEAE, the Pondweed Family Aquatic plants with submerged or floating leaves and inconspicuous flowers in summer. 1a. Leaves opposite or whorled --2. 1b. Leaves alternate --2c. 2a. Leaves thread-like, 3-8 cm. long =Horned Pondweed, Zannichellia palustris.= 2b. Leaves linear, toothed, abruptly dilated at the base, 3 cm. long or less (Naiad) --3. 2c. Leaves entire, not abruptly dilated at base [2]=Pondweed, Potamogeton spp.= 3a. Leaves about 2 mm. wide, sharply and coarsely toothed =Naiad, Naias marina.= 3b. Leaves very narrowly linear, with numerous minute teeth =Naiad, Naias flexilis.= [2] About 30 species of Potamogeton occur in Michigan, among which the most conspicuous is Potamogeton natans, with elliptical floating leaves. For the identification of the species the Manual must be used. JUNCAGINACEAE, the Arrow Grass Family 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.=