- 1s a 
: 
PONDWEED FAMILY. 77 
30. Potamogeton Spirillus Tuckerm. Spiral Pondweed. (Fig. 171.) 
Potamogeton Spirilius Tuckerm. Am. Journ. Sci. 
(II) 6: 228. 1848. 
Stems compressed, branched, 6’-20’ long, the 
‘branches often short and recurved. Floating leaves 
-oval or elliptic, obtuse, the largest about 1’ long 
and 14’ wide, with 5-13 nerves deeply impressed 
‘beneath, their petioles often 1’ long; submerged 
leaves linear, 114’/—-2’’ long, about 14’’ wide, mostly 
5-nerved ; stipules of the upper floating leaves free ; 
‘those of the submerged leaves adnate to the blade 
or petiole ; spikes above water 3’’-5’’ long, contin- 
uous, the lower mostly sessile, capitate and 1-I0- 
fruited; fruit cochleate, roundish, less than 1/” 
long, flat and deeply impressed on the sides, 3- 
keeled on the back, the middle keel winged and 
sometimes 4-5-toothed ; style deciduous ; embryo 
spiral, about 1% turns. 
In ponds and ditches, Nova Scotia and Ontario to 
Minnesota, south to Virginia, Missouri and Nebraska. 
_June-Aug. 
31. Potamogeton filiformis Pers.  Fili- 
form Pondweed. (Fig. 172.) 
Potamogeton filiformis Pers, Syn. I: 152. 1805. 
Stems from a running rootstock, slender, 3°-20° 
long, filiform above, stout and thick towards the 
base. Leaves numerous, 2/-12’ long, %’/—%4// 
wide, 1-nerved with a few cross veins; sheaths 
about 1’’ long and the free part of the stipule 14/ 
long, scarious on the edges; flowers on long, often 
recurved peduncles, 2-12 in each whorl, the whorls 
(/-1/ apart ; fruit 1//-1}4/’ long, slightly less than 
1’’ wide, the sides even, the back not keeled, the 
face nearly straight or obtusely angled near the 
top; stigma nearly or quite sessile, remaining on 
the fruit as a broad truncate projection. 
In ponds and lakes, Anticosti to western New York 
and Michigan. August. 
Potamogeton filiformis Macounii Morong; Macoun, Cat. Can. Pl. 4:88. 1888. 
Leaves 1'-3' long, the largest !4’' or more wide, obtuse, stiff, with a strong midrib and raised 
-or slightly revolute margins; fruit rarely more than 1’’ long; peduncles only 8’’-10'’ long; plant 
commonly with a compact bushy habit. In brackish or salt water lakes, prairie region of Canada. 
32. Potamogeton pectinatus I. Fennel- 
leaved Pondweed. (Fig. 173.) 
Potamogeton pectinatus I, Sp. Pl. 127. 1753. 
Stems slender, much branched, 1°-3° long, the 
branches repeatedly forking. Leaves setaceous, 
attenuate to the apex, I-nerved, 1/—6’ long, often 
capillary and nerveless; stipules half free, 14/—1’ 
long, their sheaths scarious on the margins; pe- 
duncles filiform, 2’-12’ long, the flowers in verti- 
cils; fruit obliquely obovoid, with a hard thick 
shell, 114//-2’’ long, 1//-14’’ wide, without a mid- 
dle keel, but with obscure lateral ridges on the 
back, plump on the sides and curved or occasion- 
ally a little angled on the face; style straight or 
recurved, facial; embryo apex pointing almost 
directly toward the basal end. 
In fresh, brackish or salt water, Cape Breton to Brit- 
ish Columbia, south to Florida, Texas and California. 
Alsoin Europe. July-Aug. 
