1. Herbs annual, wiry; inflorescences: branching mostly monochasial | → 2 |
1. Herbs annual or perennial, not wiry; inflorescences: branching mostly dichasial | → 3 |
2. Leaf blades linear or linear-subulate to linear-lanceolate, 5–22 mm, margins recurved to revolute; sepals 3–7 mm; capsule lengths 1–1.2 times sepals. | H. drummondii |
2. Leaf blades narrowly triangular-subulate to linear-subulate, scalelike, 1–4 mm, margins incurved; sepals 1.5–2.5 mm; capsule lengths 2–2.7 times sepals. | H. gentianoides |
3. Stems and leaves scabrous-tomentose to pilose; sepal margins setulose-ciliate. | H. setosum |
3. Stems and leaves glabrous; sepal margins sometimes ciliate, not setulose-ciliate | → 4 |
4. Leaf blades linear-subulate, 0.2–0.3 mm wide, basal veins 1, midrib unbranched. | H. cumulicola |
4. Leaf blades not linear-subulate, (0.5–)2–18 mm wide, basal veins 1–7, midrib with 0–4 pairs of branches | → 5 |
5. Leaf blades leathery; petals golden yellow or orange-yellow; stamens (35–) 50–80 | → 6 |
5. Leaf blades papery to membranous; petals usually bright, golden, or pale yellow, rarely salmon-orange; stamens 5–25 | → 11 |
6. Leaf blades linear-oblong or linear-lanceolate to linear, 0.5–2 mm wide; petals red tinged; stamens 35–50; styles 2.5–5 mm | H. paucifolium |
6. Leaf blades elliptic, lanceolate, linear-lanceolate, oblong-elliptic, obovate, or ovate, 3–18 mm wide; petals not red tinged; stamens 50–80; styles 2–4 mm | → 7 |
7. Herbs erect or ± spreading, non-aerenchymatous at base; leaves (main stems) longer than internodes | → 8 |
7. Herbs erect to ascending, usually ± aerenchymatous (spongiform-thickened) at base; leaves (main stems) mostly shorter than internodes (usually longer in. 31 H. harperi). | → 9 |
8. Leaf blades (main stem) lanceolate to oblong-elliptic or obovate, 10–30(–50) mm, apex usually acute to acuminate, rarely obtuse; subsidiary inflorescence branches with or without relatively smaller leaves. | H. virgatum |
8. Leaf blades (main stem) narrowly lanceolate, 10–40(–55) mm, apex acute to acuminate; subsidiary inflorescence branches with relatively smaller leaves. | H. radfordiorum |
9. Herbs 2–7 dm; leaf blades (main stem) usually broadly to narrowly ovate, rarely elliptic or lanceolate. | H. denticulatum |
9. Herbs 3–12 dm; leaf blades (main stem) usually lanceolate, sometimes linear-lanceolate or oblong-elliptic, rarely elliptic or ovate | → 10 |
10. Herbs erect to ascending, branching at base and in inflorescence; leaves strongly ascending to appressed, shorter than internodes, smaller distally. | H. erythreae |
10. Herbs erect, branching (from long-creeping rhizomes) at base and from mid and distal nodes; leaves ascending to deflexed, mostly longer than internodes, not or scarcely smaller distally. | H. harperi |
11. Herbs decumbent to ascending, forming loose mats; stigmas scarcely capitate. | H. anagalloides |
11. Herbs usually erect, not forming loose mats; stigmas broadly capitate | → 12 |
12. Leaf blades lanceolate, linear, narrowly elliptic, narrowly oblong-elliptic, oblanceolate, oblanceolate-linear, or obovate; capsules broadest proximal to middle | → 13 |
12. Leaf blades usually elliptic, oblong, broadly oblong-elliptic, ovate, ovate-triangular, round, or suborbiculate, rarely lanceolate; capsules usually broadest at or near middle | → 14 |
13. Leaf blades lanceolate, narrowly oblong-elliptic, or oblanceolate, (2–)6–12 mm wide, basal veins (3–)5–7; inflorescences usually compact. | H. majus |
13. Leaf blades linear to oblanceolate-linear or (proximal) oblanceolate to obovate, 0.5–5.5 mm wide, basal veins 1–3(–5); inflorescences usually diffuse. | H. canadense |
14. Leaf blades (mid and distal) lanceolate-deltate, apex usually subacute; capsules narrowly conic-ellipsoid. | H. gymnanthum |
14. Leaf blades (mid and distal) elliptic, lanceolate, oblanceolate, oblong, round, suborbiculate, or ovate, apex obtuse to rounded; capsules narrowly ovoid to cylindric-ellipsoid | → 15 |
15. Leaf blades bicolor, paler abaxially; inflorescences: bracts linear-subulate. | H. mutilum |
15. Leaf blades concolor; inflorescences: bracts not linear-subulate. | H. boreale |