19a. Leaves opposite or in whorls of four 119a, in =COMPOSITAE=, p. 123.

19b. Leaves in whorls of 5-12 =CERATOPHYLLACEAE=, p. 34.

20a. Plants small, flattened, rounded or ovate, without distinction of stem and leaf; the whole plant floating on or near the surface =LEMNACEAE=, p. 9.

20b. Plant attached to the soil, with differentiated stem and leaves --21.

21a. Leaves on long slender stalks, which bear also a cl.u.s.ter of slender tubers near the leaf-base; leaves heart-shape 1b, in =GENTIANACEAE=, p. 88.

21b. Leaf-stalks without a cl.u.s.ter of tubers --22.

22a. Leaves all basal --23.

22b. Stem-leaves present --24.

23a. Leaves parallel-veined 1b, in =ALISMACEAE=, p. 3.

23b. Leaves net-veined 1b, in =NYMPHAEACEAE=, p. 35.

24a. Leaves opposite or whorled --25.

24b. Leaves alternate --26.

25a. Leaves less than 2 cm. long =CALLITRICHACEAE=, p. 68.

25b. Leaves more than 2 cm. long 1b, in =NAJADACEAE=, p. 2.

26a. Leaves attached by the center to the stalk 2b, in =NYMPHAEACEAE=, p. 35.

26b. Leaves attached by the margin --27.

27a. Leaves parallel-veined --28.

27b. Leaves net-veined, with a single mid-vein; lanceolate or elliptical in outline 29b, in =POLYGONACEAE=, p. 28.

28a. Leaves not over 2 dm. long 1b, in =NAJADACEAE=, p. 2.

28b. Leaves very long and gra.s.s-like 14a, in =GRAMINEAE=, p. 5.

29a. Brown, yellow, or white plants, without green color --30.

29b. Plants with normal green color, at least in some parts --33.

30a. Stemless and leafless plants, consisting of flowers only and partly underground 4a, in =ARACEAE=, p. 8.

30b. Stems climbing on other plants 1b, in =CONVOLVULACEAE=, p. 91.

30c. Stem and flower-stalks erect, not climbing --31.

31a. Corolla regular; stamens 6-12 1a, in =ERICACEAE=, p. 84.

31b. Corolla irregular --32.

32a. Sepals and petals each 3; flowers in simple racemes 5a, in =ORCHIDACEAE=, p. 16.

32b. Sepals 5; corolla of united petals =OROBANCHACEAE=, p. 106.

33a. Stem thick and fleshy, leafless, th.o.r.n.y =CACTACEAE=, p. 77.

33b. Stem not th.o.r.n.y --34.

34a. Leaves none --35.

34b. Leaves reduced to small scales --40.

34c. Leaves thick and fleshy --44.

34d. Leaves hollow --45.

34e. Leaves small, all basal, bearing large glandular hairs on the upper surface =DROSERACEAE=, p. 48.

35a. Stem none, the flowers appearing at or partially beneath the surface of the soil 4a, in =ARACEAE=, p. 8.

35b. Stem present --36.

36a. Stem freely branched 2a, in =LILIACEAE=, p. 10.

36b. Stem unbranched, except possibly in the flower-cl.u.s.ters --37.

37a. Flowers greenish or brownish, without obvious colored petals --38.

37b. Flowers with conspicuous white or colored petals --39.

38a. Each flower with 6 small chaffy petals 4, in =JUNCACEAE=, p. 10.

38b. Petals none; each flower in the axil of a single chaffy bract 2a, in =CYPERACEAE=, p. 7.

39a. Flowers regular 34a, in =LILIACEAE=, p. 11.

39b. Flowers irregular 10a, in =ORCHIDACEAE=, p. 16.

40a. Stem erect, unbranched or with one or two branches only --41.

40b. Stem freely branched --42.

41a. Plants of moist soil, with opposite scales; corolla regular, with 4 petal-like lobes 1a, in =GENTIANACEAE=, p. 88.

41b. Swamp plants, with a few alternate scales; corolla irregular =LENTIBULARIACEAE=, p. 105.