KEY* TO SELECTED FAMILIES BASED ON INTERNAL ANATOMY

1. Embryo with two (rarely one) cotyledons
2. Cotyledons thin, bent or folded laterally (radicle-hypocotyl may not be bent)
3. External cotyledon slightly laterally bent, seeds oblong CRUCIFERAE
3. Cotyledons strongly folded, seeds often sectoroid
4. Radicle-hypocotyl curved-encircling, cotyledons folded laterally MALVACEAE
4. Radicle-hypocotyl ± straight, cotyledons doubly folded CONVOVULACEAE

2. Cotyledons not folded nor bent laterally
5. Embryo encircling or coiled
6. Embryo filling entire seed
7. Embryo coiled CHENOPODIACEAE
7. Embryo not coiled
8. Hilum inconspicuous CRUCIFERAE
8. Hilum conspicuous LEGUMINOSAE
6. Nutritive tissue evident, usually abundant
9. Hilum basal, seeds triangular or lenticular in cross-section POLYGONACEAE
9. Hilum basolateral to lateral
10. Embryo encircling, external
11. Seeds papillate or colliculose with cell margins wavy CARYOPHYLLACEAE
11. Seeds smooth, cell margins not wavy
12. Embryo bent
13. Cotyledons much larger than radicle ANACARDIACEAE
13. Cotyledons smaller than radicle Echinocactus
12. Embryo encircling
14. Pericarp ± adherent, seeds black CHENOPODIACEAE
14. Pericarp not adherent, conspicuous rim, seeds red AMARANTHACEAE
10. Embryo surrounded by 'endosperm'
15. Cotyledons narrow, endosperm extensive, embryo usually encircling SOLANACEAE
15. Cotyledons broader than radicle, endosperm scanty LEGUMINOSAE
5. Embryo straight
16. Nutritive tissue absent or scanty
17. Hilum basolateral, conspicuous; seeds sectoroid LABIATEAE
17. Hilum usually inconspicuous
18. Seeds elongate ob-pyramidal COMPOSITAE
18. Seeds sectoroid, often with appendages ROSACEAE
16. Nutritive tissue evident
19. 'Seeds' (mericarps), ribbed, with oil glands UMBELLIFERAE
19. True seeds, without oil glands
20. Hilum lateral
21. Cotyledons slightly broader than radicle, seeds sulcate PLANTAGINACEAE
21. Cotyledons much broader than radicle, cell margines wavy CARYOPHYLLACEAE
20. Hilum basal or basolateral
22. Seed with funiculus, often with caruncle EUPHORBIACEAE
22. Without funiculus and caruncle
23. Cotyledons much broader than radicle LEGUMINOSAE
23. Cotyledons narrow, embryo + coiled SOLANACEAE
1. Embryo without leaf-like cotyledons
24. Embryo spirally coiled, nutritive tissue scanty CONVOVULACEAE
24. Embryo not coiled, nutritive tissue abundant
25. Embryo (basolateral) region visible externally, caryopsis circular in cross-section, enclosed by ± leafy palea and lemma GRAMINEAE
25. Embryo (basal) region not visible externally, achene enclosed by perigynia or surrounded by narrow bristles CYPERACEAE

*BASED ON
Duane Isely. 1947.
Investigations in seed classification by family characteristics.
Iowa State Univ. Agric. Exp. Stat. Res. Bull. 351:317-380.