2a. Leaves thread-like, 3-8 cm. long =Horned Pondweed, Zannich.e.l.lia pal.u.s.tris.=

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 coa.r.s.ely 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 Gra.s.s 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 Gra.s.s) --2.

1b. Stem-leaves present; flowers in a loose bracted raceme (1-3 dm.

high). =Scheuchzeria, Scheuchzeria pal.u.s.tris.=

2a. Fruit (usually to be seen at the base of the raceme) ovoid or oblong, rounded at the base =Arrow Gra.s.s, Triglochin maritima.=

2b. Fruit linear, narrowed at the base (1-5 dm. high) =Arrow Gra.s.s, Triglochin pal.u.s.tris.=

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 Gra.s.s, Vallisneria spiralis.=

1b. Leaves on the stem, 2 cm. long or less =Water-weed, Elodea canadensis.=

GRAMINEAE, the Gra.s.s Family

Gra.s.ses, with linear or narrow sheathing leaves, and very small flowers without perianth in the axils of chaffy bracts, appearing in late spring and summer.

Of the large number (over 150) of gra.s.ses in Michigan, only the commonest are included here, and the student is referred to the Manuals for a full treatment of them.

Their cla.s.sification depends chiefly upon the structure and arrangement of the spikelets. These consist typically of a short axis, the rachilla, almost or quite concealed by several chaffy bracts. The two lower bracts are termed glumes, and have no flowers in their axils. Above the glumes are two or more other bracts, the lemmas. In the axil of each lemma, and usually concealed by it, is a smaller bract, the palea, and between the lemma and the palea is a single flower. The number of flowers in a spikelet is therefore normally equal to the number of lemmas. The spikelets are grouped in racemes, spikes, or panicles of various size.

1a. Spikelets one-flowered --2.

1b. Spikelets with 2 or more flowers --24.

2a. Spikelets grouped into dense solitary cylindrical spikes --3.

2b. Spikelets arranged in panicles or in panicled spikes --8.

3a. Spikelets without awns or bristles, or with short awns not more than 3 mm. long --4.

3b. Spikelets with awns 2-5 cm. long, terminating the bracts =Squirrel-tail, Hordeum jubatum.=