| 1a. Twining plants, with flowers in panicles or racemes | DIOSCOREACEAE, p. 14. |
| 1b. Plants with milky juice | 13a, in COMPOSITAE, p. 115. |
| 1c. Plants not twining (some climb by tendrils) and not with milky juice. — 2. | |
| 2a. Flowers in close spikes or heads, surrounded or subtended by a green or colored bract, the whole resembling a single flower; petals minute or wanting; leaves broad, not grass-like, linear, or sword-shape | ARACEAE, p. 8. |
| 2b. Plants with narrow, linear, grass-like, or sword-shape leaves (a few species of Carex have broader, lanceolate to ovate leaves); flowers greenish, yellowish, or brownish, never brightly colored, and frequently dry or chaffy in texture; perianth small or wanting; individual flowers inconspicuous in size, but sometimes grouped into conspicuous clusters — 3. | |
| 2c. Plants with leaves of various widths, but the flowers petaloid, i. e., with a white or colored, more or less conspicuous perianth, and never chaffy in texture. In a few cases the flowers are greenish, but the size and conspicuousness of the perianth identifies them in this class — 9. | |
| 3a. Flowers in the axils of dry, membranous or chaffy scales, which are regularly arranged into spikes or spikelets of uniform size and structure, which are variously grouped or clustered; fruit an achene; grasses and sedges, with joined stems and sheathing leaves, or leafless and the stems not jointed — 4. | |
| 3b. Flowers not subtended individually by dry, membranous, or chaffy scales, and otherwise not agreeing with 3a — 5. | |
| 4a. Leaf-sheaths split on the side opposite the leaf; leaves usually 2-ranked, i. e., in 2 longitudinal rows with the third leaf above the first; stems rounded or flat, never triangular, usually hollow | GRAMINEAE, p. 4. |
| 4b. Leaf-sheaths closed into a continuous tube; leaves usually 3-ranked; stems frequently triangular, usually solid | CYPERACEAE, p. 7. |
| 5a. Flowers in dense spikes — 6. | |
| 5b. Flowers in heads, racemes, or panicles — 7. | |
| 6a. Spike terminal, with pistillate flowers at the base and staminate ones at the apex | TYPHACEAE, p. 2. |
| 6b. Spike short, apparently lateral, near the apex of the stem | 3a, in ARACEAE, p. 8. |
| 7a. Flowers in globose heads which are arranged in spikes, the lowest heads pistillate, the upper staminate; ovary 1-celled | SPARGANIACEAE, p. 2. |
| 7b. Flowers in globose woolly heads terminating leafless unbranched stalks | ERIOCAULACEAE, p. 9. |
| 7c. Flowers in a spike-like raceme; ovaries 3-6, separate or nearly so | JUNCAGINACEAE, p. 3. |
| 7d. Flowers in heads or panicles, all perfect, not woolly, with one ovary — 8. | |
| 8a. Leaves less than 1 cm. wide, or none; divisions of the perianth 6 | JUNCACEAE, p. 10. |
| 8b. Leaves 2 cm. wide or more; petals 5 | 2a, in UMBELLIFERAE, p. 80. |
| 9a. Flowers regular, with all the petals of approximately the same size and shape — 10. | |
| 9b. Flowers irregular, with the petals of each flower not of the same size or shape — 22. | |
| 10a. Ovaries 3 or more, separate or barely united with each other at the base — 11. | |
| 10b. Ovary one in each flower — 12. | |
| 11a. Ovaries 3-6 in number; flowers in spikes or racemes; leaves linear | JUNCAGINACEAE, p. 3. |
| 11b. Ovaries more than 6 | ALISMACEAE, p. 3. |
| 12a. Flowers or flower-clusters lateral, axillary or apparently so — 13. | |
| 12b. Flowers or flower-clusters terminal or on leafless stalks — 14. | |
| 13a. Leaves minute and scale-like; flowers greenish-yellow | 2a, in LILIACEAE, p. 10. |
| 13b. Leaves linear, grass-like | 3b, in IRIDACEAE, p. 13. |
| 13c. Leaves lanceolate or broader, not grass-like or scale-like | 2b, in LILIACEAE, p. 10. |
| 14a. Divisions of the perianth 5-12 cm. long — 15. | |
| 14b. Divisions of the perianth less than 5 cm. long — 16. | |
| 15a. Flowers blue, or blue marked with yellow | 1a, in IRIDACEAE, p. 15. |
| 15b. Flowers not blue | 12a, in LILIACEAE, p. 11. |
| 16a. Flowers solitary — 17. | |
| 16b. Flowers 2 or more, in some kind of a cluster — 18. | |
| 17a. Leaves 2, broadly heart-shape, basal, on long stalks | 1b, in ARISTOLOCHIACEAE, p. 25. |
| 17b. Leaves not heart-shape 20, | 20, in LILIACEAE, p. 12. |
| 18a. Divisions of the perianth (4 to 6) all essentially alike — 19. | |
| 18b. Perianth differentiated into sepals and 2 or 3 colored petals — 21. | |
| 19a. Flowers in umbels — 20. | |
| 19b. Flowers in dense round heads; petals 5 | 2a, in UMBELLIFERAE, p. 80. |
| 19c. Flowers in spikes, racemes, or panicles | 38, in LILIACEAE, p. 13. |
| 20a. Ovary inferior, appearing below the perianth as a swelling at the apex of the stalk; flowers bright yellow; leaves linear | AMARYLLIDACEAE, p. 14. |
| 20b. Ovary inferior; flowers blue or white, terminating a flattened winged leafless flower-stalk | 3a, in IRIDACEAE, p. 15. |
| 20c. Ovary superior, i. e., in the center of the flower and separate from the perianth | 31, in LILIACEAE, p. 13. |
| 21a. Flowers in dense heads, yellow, 1 cm. wide or smaller | XYRIDACEAE, p. 9. |
| 21b. Flowers in umbels, blue or white, 2 cm. wide or larger | COMMELINACEAE, p. 9. |
| 22a. Flowers blue; ovary superior (defined under 20c); stamens distinct from the other parts of the flower — 23. | |
| 22b. Ovary inferior (defined under 20a); floral structure complex; stamens attached to other parts of the flower and not resembling ordinary stamens in form or structure | ORCHIDACEAE, p. 15. |
| 23a. Leaves triangular-heart-shape at base; marsh plants | 1a, in PONTEDERIACEAE, p. 10. |
| 23b. Leaves not heart-shape at base | COMMELINACEAE, p. 9. |