PONDWEED FAMILY. 81 
2. Naias fléxilis (Willd.) Rost. & Schmidt. Slender Naias. (Fig. 180.) 
Eee Slexilis Willd. Abh. Akad. Berlin, 95. 
Naias flexilis Rost. & Schmidt, Fl.Sed.384. 1824. 
Stem slender, forking. Leaves linear, pel- 
lucid, acuminate or abruptly acute, %/—1’ 
long, %4//-1’/’ wide, numerous and crowded 
on the upper parts of the branches, with 25-30 
minute teeth on each edge; sheaths obliquely 
rounded with 5-10 teeth on each margin ; 
fruit ellipsoid with very thin pericarp, 1//-2’’ 
long, 4’/-4’’ in diameter ; style long, per- 
sistent ; stigmas short; seed smooth, shin- 
ing, straw-colored, sculptured, though some- 
times quite faintly, with 30-40 rows of nearly 
square or hexagonal reticulations which are 
scarcely seen through the dark pericarp. 
In ponds and streams throughout nearly all 
North America. Alsoin Europe. Summer. 
Naias fléxilis robusta Morong, Coult. Bot. Gaz. 10: 255. 1885. 
Stem stout, few-leaved, 3°-6° long; internodes 
long. Massachusetts to Michigan and Texas. 
3. Naias Guadalupénsis (Spreng. ) 
Morong. Guadaloupe Naias. 
(Fig. 181.) 
FI Guadalupensits Spreng. Syst. 1: 20. 
Naias. Guadalupensis Morong, Mem. Torr, Club, 
3: Part 2,60. 1893. 
Stem nearly capillary, 1°-2° long, widely 
branched from the base. Leaves numerous, 
6/’-9 long, %’/-%4’’ wide, acute, opposite or 
in fascicles of 2-5, frequently recurved, with 
sheaths and teeth like those of NV. fleailis but 
generally with 40-50 teeth on each margin of 
the leaf; fruit about 1// long ; pericarp dark and 
strongly marked by 16-20 rows of hexagonal or 
rectangular reticulations which are transversely 
oblong ; seed straw-colored, not shining. 
In ponds and lakes, Nebraska to Oregon and 
Texas, east to Florida. Also in tropical America. 
July—Sept. 
4. Naias gracillima (A. Br.) Morong. ‘Thread-like Naias. (Fig. 182.) 
Naias Indica var. gracillima A. Br.; Engelm. in 
A. Gray, Man. Ed. 5, 681. _ 1867. 
Naias gracillima Morong, Mem. Torr. Club, 3: 
Part 2, 61. 1893. 
Dioecious, stem capillary, 6/-15’ long, much 
branched, the branches alternate. Leaves nu- 
merous, opposite or often fascicled in 3’s—5’s or 
more, setaceous, 1%4’-2/ long, usually with about 
20 minute teeth on each margin ; sheaths auri- 
cled, with 6 or 7 teeth on each auricle, the teeth 
standing upon setaceous divisions of the sheath ; 
stigmas very short ; fruit oblong-cylindric, %4/’ 
long, 4’ in diameter, slightly curved inwardly 
or straight, the pericarp straw-colored or pur- 
plish, marked by about 25 rows of irregularly 
oblong reticulations ; seed not shining. 
In pools and ponds, eastern Massachusetts to 
Delaware, Pennsylvinia and Missouri. July—Sept. 
6 
