15(14). Submerged plants mainly of salt-water gulfs and bays, occasionally 

 inland in brackish or fresh-water (16) 



15. Plants terrestrial or (if in water) at least partly or wholly emersed (18) 



16(15). Plants perennial, entirely marine; leaves strap-shaped, leathery, at least 

 5 mm. wide, essentially entire; rhizome and stem thick and woody, 

 the rhizome with persistent fibers from the nodes, the stem adorned 



with the persistent fibrous leaf bases; flowers spicate 



19. Posidoniaceae, p. 129 



16. Plants of fresh, brackish or salt-water; leaves linear, entire or toothed; 



rhizome and stem not thick and woody, not provided with fibers or 

 persistent fibrous leaf bases; flowers axillary, solitary or cymose (17) 



17(16). Carpels 2 or more, rarely solitary; ovule pendulous; perennials 



16. Zannichelliaceae , p. 1 17 



17. Carpels solitary; ovule basal, erect; annuals 18. Najadaceae, p. 123 



18(15). Flowers ebracteate; small herbs with narrow grasslike basal leaves and 



slender spikelike racemes of small usually greenish flowers 



20. Juncaginaceae, p. 129 



18. Flowers with bracts, bractlets, scales or glumes (19) 



19(18). Proper perianth absent or nearly so, the flowers borne in dense heads, 

 spikes or racemes or thickly crowded on a fleshy axis or else vari- 

 ously disposed in panicles, when genitalia subtended by scalelike 

 structures these never numbering precisely 3 in 1 series or 6 in 2 

 series (20) 



19. Proper perianth present, often in 2 series of 3 members each (in some 



families the outer or inner or both series scalelike (25) 



20(19). Flowers crowded on a terminal elongate fleshy axis which below the 

 flowering zone usually has a large foliaceous partially or wholly 

 sheathing bract (spathe) which covers the inflorescence during its 

 early development..... 27. Araceae, p. 556 



20. Axis of inflorescence not fleshy; bract (if present) not so large and not cover- 



ing the young inflorescence (21) 



21(20). Inflorescence a series of globose heads at the upper nodes, the uppermost 



heads of staminate flowers, the lower ones of pistillate flowers 



14. Sparganiaceae, p. 89 



21. Inflorescence otherwise (22) 



22(21). Inflorescence solitary, terminal, globose or hemispheric, 2-15 mm. thick, 

 exceedingly dense, not subtended by large bracts (bracts only 1-4 

 mm. long) 31. Eriocaulaceae, p. 588 



22. Inflorescences not globose nor hemispheric or if so (as in some Cyperaceae) 



then closely subtended by several bracts several times as long as the 

 inflorescence is thick (23) 



23(22). Inflorescence a very dense brownish spike 12-40 cm. long and 1-2 cm. 

 thick with thousands of minute flowers, the male above, the female 

 below; "cat-tails" 13. Typhaceae, p. 85 



23. Inflorescence otherwise (24) 



24(23). Leaves distichous (and sometimes equitant); with rare exceptions each 

 floret subtended by 2 scales (the lower or lemma abaxial and with 

 1 midvein; the upper or palea adaxial and with 2 unequal non- 

 medial nerves) 24. Gramineae, p. 169 



21 



