Cistaceae, the Rock-rose Family
Small herbs or shrubs, with opposite or alternate entire leaves; flowers regular, with 5 sepals, 3 or 5 petals, and 3 to many stamens.
| 1a. Flowers yellow (early summer) — 2. | |
| 1b. Flowers greenish or purplish, minute, in panicles (late summer) (Pinweed) — 4. | |
| 2a. Leaves crowded, closely appressed to the branches; flowers 7 mm. wide (2-4 dm. high) | False Heather, Hudsonia tomentosa. |
| 2b. Leaves spreading; flowers 15-30 mm. wide (3-6 dm. high) (Frostweed) — 3. | |
| 3a. Petal-bearing flowers solitary | Frostweed, Helianthemum canadense. |
| 3b. Petal-bearing flowers few, racemose | Frostweed, Helianthemum majus. |
| 4a. Stem-leaves linear, 4 or more times as long as wide — 5. | |
| 4b. Stem-leaves oblong or elliptical, about 3 times as long as wide (2-6 dm. tall) — 8. | |
| 5a. Plant pale with dense appressed pubescence (2-4 dm. high) | Pinweed, Lechea stricta. |
| 5b. Plant green, pubescence sparse or none — 6. | |
| 6a. Leaves thread-like, seldom exceeding 1 mm. in width (1-3 dm. tall) | Pinweed, Lechea tenuifolia. |
| 6b. Leaves 1-5 mm. wide (2-6 dm. high) — 7. | |
| 7a. Leaves on the basal shoots narrowly lanceolate | Pinweed, Lechea intermedia. |
| 7b. Leaves on the basal shoots oblong-elliptic, about twice as long as wide | Pinweed, Lechea racemulosa. |
| 8a. Pubescence of spreading hairs | Pinweed, Lechea villosa. |
| 8b. Pubescence of appressed hairs | Pinweed, Lechea minor. |