not only from our region but from elsewhere, do not readily fall into either of 

 these categories, although they have some characteristics attributed to one or the 

 other of these plants. Although we would not be adverse to considering these 

 plants as one complex entity, we have followed their traditional treatment as 

 maintained by Fernald. 



Fam. 15. Potamogetonaceae Dum. Pondweed Family 



Aquatic herbs of fresh or sometimes brackish or alkaline water; leaves alternate 

 or imperfectly opposite, those immersed thin, those above water often leathery, 

 sheathing at the base, the sheath free or partially adnate to the petiole; flowers 

 bisexual, small, arranged in pedunculate axillary spikes; peduncle surrounded by 

 a sheath at the base; bracts absent; perianth comprised of 4 free rounded shortly 

 clawed valvate segments; stamens 4, inserted on the claws of the segments; 

 anthers extrorse, 2-celled, sessile; gynoecium of 4 sessile free 1 -celled carpels; 

 stigmas sessile or on short styles; ovule solitary, attached to the adaxial angle of 

 the carpel, campylotropous; fruiting carpels sessile, free, 1-seeded, indehiscent; 

 seeds without endosperm, the embryo with large "foot", the plumule enclosed 

 by the cotyledon. 



A family of two widespread genera, the following and Groenlandia. 



1. Potamogeton L. Pondweed 



Annual or perennial aquatic herbs propagated from seeds, winter-buds 

 (hibernacula) or rhizomes; stems variable in length according to water depth, 

 branched or unbranched, terete or flattened; leaves all submersed or with both 

 submersed and floating blades; submersed leaves usually flaccid, sessile or petioled, 

 linear or orbicular, acute to obtuse at apex, the margins entire to denticulate or 

 serrate, the nerves 1 to 35; stipules fused to form a single structure with 2 

 midveins, arising from the axil of the stem and leaf, free or adnate to the leaf 

 base, often sheathing the stem and sometimes with the outer margins partially 

 fused (connate); floating leaves usually coriaceous, petioled, elliptic to ovate, 

 cuneate to rounded or cordate at base, the nerves 3 to 51, the margins entire, the 

 stipules like those of submersed leaves but never adnate nor connate; peduncles 

 about same diameter as stem, terete, sometimes clavate at tip; inflorescence a 

 spike with 1 to 20 whorls of flowers, compact or moniliform, with 2 to 4 flowers 

 in each whorl, mostly buoyed above the water surface; flowers bisexual, perianth 

 of 4 free rounded short-clawed greenish segments; stamens 4; anthers sessile on 

 the claws, 2-celIed, extrorse; carpels 4, free, sessile; fruits dryish drupelets or 

 achenes with spongy mesocarp and bony endocarp. one-seeded, embryo coiled, 

 cotyledon one, endosperm absent. 



A genus of 90 to 100 species found in all parts of the world, except the polar 

 regions, but mostly in the North Temperate areas. Nearly 40 species occur in 

 North America, all but one being indigenous; about half of these are widespread, 

 common and often locally abundant. 



Pondweeds are found primarily in shallow ponds, lakes and quiet waters of 

 rivers and streams, and they are an important element in the ecology of such 

 places. The achenes of all our species provide a favorite and important food for 

 wildfowl. In addition, plant parts, especially of the more delicate species, are also 

 eaten by wildfowl that include most waterfowl, marsh birds and shorebirds. The 

 plants are also commonly eaten by muskrats, beaver and deer. The most important 

 species, mainly because of its tolerance to brackish water, its abundant seed pro- 

 duction, and the edibility of its vegetative parts, is the sago pondweed (P. 

 pectinatus). Most of the species provide food, shelter and shade for fish and 

 minute animal life. They provide, in particular, an excellent haven for insect life 

 that, in turn, provide food for fish. 



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