20 ZANNICHELLIACEAE 



Leaves rounded-ovate to short-lanceolate, araplexicaul, not cucullate; the 

 curved embryo pointing inside the base of the fruit. 11. P. Richardsonii. 



Leaves narrowly Linear to capillary. 



Stipules free from the petioles and the leaf-blades. 

 Leaves 1.5-4 mm. wide. 



Species without glands at the base of the leaves; leaves with 3 principal 



nerves and several fine ones. 12. P. compressus. 



Species with glands at the base of the leaves. 



Glands large and translucent; nerves mostly 3; the curved end of tlie 



embryo pointing inside the base of the fruit. 13. P. obtusifolius. 



Glands small, dull; nerves of the leaves .5-7; the straight end of the 

 embryo pointing to the base of the fruit. 1-4. P. Friesii. 



Leaves seldom more than 1.5 mm. wide, often less. 



Glands absent; nutlets keeled. 15. P. foliosus. 



Glands present; nutlets not keeled. 16. P. pusillus. 



Stipules adnate to the base of the leaves. 



Leaves 1.5 mm. wide or less, with entire margins. 



Stigma broad, sessile; nutlets indistinctly 1-keeled or keel-less. 



Leaves filiform, less than 0.5 mm. wide; stipular sheaths 3-8 mm. long. 



17. P. filiformis. 

 Leaves about 1 mm. wide; stipular sheaths 1-2 cm. long. 



18. P. interior. 

 Stigma capitate, on an evident style: nutlets with 2 lateral but no median 



keel. 19. P. pectinalus. 



Leaves several-nerved, 3-6 mm. wide, finely serrulate seen under a lens. 



20. P. Robbinsii. 



2. RUPPIA L. 



Sheaths 6-10 mm. long; drupe about 2 mm. long or less. 



Drupe very oblique; beak 0.5-1 mm. long. 1. R. marilima. 



Drupe scarcely oblique, almost beakless. 2. R. pectinata. 



Sheaths 20-40 mm. long; drupe 3-4 mm. long. 3. R. occidentalis. 



3. ZANNICHELLIA (Mich.) L. i. Z. palustris. 



Family 8. NAJADACEAE. Najas Family. 

 1. NAJAS L. 



Leaves 1-3 mm. wide, coarsely toothed; back of the leaves and internodes spiny; plant 

 dioecious. 1. iV. marina. 



Leaves 0.5—1 mm. wide, finely, almost microscopically serrulate; back of the leaves and 

 internodes imarmed; plant monoecious. 

 Drupe shinmg, with 30-50 rows of indistinct reticulations. 2. iV. flexilis. 



Drupe dull, with 16-20 rows of strongly marked reticulations. 3. N. guadalupensis. 



Family 9. SCHEUCHZERIACEAE. Arrow-grass Family. 



Stem scapose; leaves all basal ; flowers spicate or racemose. 1. Triglochin. 



Stem leafy; flowers few, in loose racemes. 2. Scheuchzeri.\. 



1. TRIGLOCHIN L. Arrow-grass. 



Carpels 3; fruit linear -clavate, tapering at the base. 1. T. paluitris. 



Carpels 6; fruit oblong or ovoid, obtuse at the base. 2. 7. marilima. 



2. SCHEUCHZERIA L. i. s. paiusiris. 



Family 10. ALISMACEAE. Water-plant.\in Family. 



Carpels in a ring on a small flat receptacle; flowers perfect. 1. Alis\l\. 



Carpels in several series on a convex receptacle; flowers monoecious or dioecious. 



2. S.\GITTARIA. 



1. ALISMA L. Water-plantain. 



Acbenes longer than wide, grooved on the back, their inner edges not meeting; pedicels 



straight, ascending. 1. A. brevipes. 



Achenes as wide as long, ribbed on the back, their inner edges meeting; pedicels recurved. 



2. A. Geyeri. 



2. SAGITTARIA L. Arrow-head, Swan or Swamp Potato. 



Leaf-blades usually without basal lobes; beak borne below the top of the achenes. 



1. S. graminea. 

 Leaf-blades or some of them sagittate or hastate, with basal lobes ; beak borne at the top 

 of the achenes. 

 Beak short, erect; bracts lanceolate or linear-lanceolate. 



Basal lobes of the leaves acute or acuminate. 2. 5. cuneata. 



Basal lobes of the leaves rounded or obtuse. 3. S. hebetiloba. 



Beak of the achenes horizontal. 



Beak short; basal lobes of the leaves at least twice as long as the terminal one; 

 bracts lanceolate. 4. A', longiloba. 



Beak long; basal lobes of the leaves usually shorter than the terminal one; bracts 

 ovate. 5. S. latifolia. 



