BUR-REED FAMILY 



83 



6. Sparganium minimum Fries. 

 Small Bur- reed. Fig. 172. 



sparganium minimum Fries, Summa Veg. Scand. 2: 560. 1S49. 



Stem floating and elongated, or decumbent, ascending or 

 erect, and relatively short. Leaves dark green, flat, narrow, 

 mostly 2i-7 mm. wide ; tlie sheaths of the upper leaves dilated 

 but not scarious-margined ; inflorescence simple, the pistillate 

 heads solitary or 2 or 3 and placed about equally distant, 

 axillary ; fruiting heads about 5 mm. in diameter ; achenes 

 short stipitate, about 3 mm. long, broadly ellipsoid, usually 

 constricted below the middle, dull greenish brown ; stigma 

 obliquely oblong or oval. 



In ponds and streams of the cooler regions of the northern hemi- 

 sphere; Swan Lake, Vancouver Island, and Mount Rainier. Type lo- 

 cality: Sweden. 



Family 3. ZANNICHELLIACEAE. 

 PoNDWEED Family. 



Perennial fresh-water plants with floating or submerged leaves or both. Leaves 

 petioled or sessile, capillary or expanded into a proper blade, or rarely reduced to 

 terete phyllodes. Flowers perfect or monoecious, in sessile or peduncled spikes 

 or in small axillary clusters. Perianth none, but flowers sometimes enclosed in 

 a hvaline sheath. Stamens 1-4; anthers extrorse, 1-2-celled, the connective some- 

 times becoming perianth-like. Pistils of 1-4 distinct carpels. Fruits of small 

 drupelets, sessile or stipitate. Endosperm wanting. 



About 4 genera and 70 species of wide geographic distribution, most abundant in north temperate regions. 



Flowers perfect; stamens 2 or 4. 



Stamens 4; drupelets sessile. L Potamogeton. 



Stamens 2; drupelets stipitate. 2. Ruppia. 



Flowers monoecious; stamen 1. 3. Zannichellia. 



1. POTAMOGETON L. 



1753. 



Sp. PI. 126. 



Leaves alternate or the uppermost opposite, often of two kinds, submerged and floating, 

 the submerged mostly linear, the floating petioled, coriaceous, lanceolate or broader. Stipules 

 membranaceous, more or less united and sheathing, free or connate to the base of the leaf or 

 petiole. Spikes sheathed by the stipules in the bud, mostly raised on a peduncle to the surface 

 of the water. Sepals 4, rounded, valvate in the bud, green or reddish. Stainens 4 opposite 

 the sepals; anthers 2-celled. Ovaries 4, sessile, distinct, 1-celled, 1-ovuled, attenuated into 

 a short recurved style, or with a sessile stigma. Fruit of 4 ovoid or subglobose drupelets, 

 the pericarp usually thin and hard or spongy. Seeds crustaceous, campylotropous, with an 

 imcinate embryo thickened at the radicular end. [Greek, in allusion to the aquatic habit.] 



A genus of about 65 species, inhabiting temperate regions. Type species, Potamogeton natans L. 



Leaves of 2 kinds, floating and submerged, the former coriaceous with a dilated blade, petioled, different in 

 form from the submerged thinner ones. 

 Submerged leaves filiform or linear, not over 4 mm. wide. 

 Spikes all alike, cylindric. 



Submerged leaves filiform; floating leaves, subcordate at base. 1. P. natans. 



Submerged leaves narrowly linear-lanceolate, 2-4 mm. wide; floating leaves attenuate into the 

 petiole. 4. P. epihydnis. 



Spikes of 2 kinds, the emersed cylindric, many-flowered, the submerged capitate, few-flowered. 



Peduncles of the submerged spikes equaling or exceeding the spikes. 2. P. diversifoliiis. 



Peduncles of the submerged spikes shorter than the spikes. 3. P. dimorphus. 



Svibmerged leaves lanceolate to ovate, when approaching linear at least over 4 mm. 

 Floating leaves 30-50-nerved. 

 Floating leaves with fewer nerves. 



Submerged leaves, at least all but the lowest, sessile. 

 Submerged leaves serrulate at apex. 

 Submerged leaves entire. 



Upper leaves and spikes reddish; submerged leaves lanceolate. 

 Upper leaves and spikes green; sul)merged leaves linear. 

 Submerged leaves all petioled. 



wide. 



5. P. amplifalius. 



6. P. angitstifolius. 



P. 

 P. 



alpiiius. 

 heterophyllus. 



9. P. americanus. 



