Linaceae, the Flax Family
Herbs with simple leaves, and regular flowers, having 5 sepals, 5 yellow or blue petals, 5 stamens, and 5 styles.
| 1a. Flowers blue (3-6 dm. high; summer) | Flax, Linum usitatissimum. |
| 1b. Flowers yellow (3-8 dm. high; summer) (Wild Flax) — 2. | |
| 2a. Middle stem-leaves below the branches opposite | Wild Flax, Linum striatum. |
| 2b. Middle stem-leaves below the branches alternate — 3. | |
| 3a. Leaves narrowly lanceolate to linear, 1-4 mm. wide — 4. | |
| 3b. Leaves oblanceolate to oblong, 4-6 mm. wide | Wild Flax, Linum virginianum. |
| 4a. Leaves entire | Wild Flax, Linum medium. |
| 4b. Upper leaves glandular-ciliate | Wild Flax, Linum sulcatum. |