| | 1. Leaf coarsely spine-toothed, stiff, 1–3 mm wide, bright green; internodes often minutely spiny; fruit generally << 5 mm, 2–3 mm wide; dioecious |
| N. marina |
| | 1' Leaf entire to minutely toothed (at 20× magnification), flexible, 0.1–2 mm wide, light to olive-green or reddish; internodes not spiny; fruit generally < 3 mm, < 2 mm wide; monoecious |
| |
| | 2. Leaf sheath appendages obvious, rounded to acuminate |
| |
| | 3. Leaf thread-like, not recurved; fruit linear-oblong, often slightly curved, net-like surface with angular spaces longer than wide |
| N. gracillima |
| | 3' Leaf linear, often recurved; fruit oblong or elliptic in outline, generally straight, net-like surface with angular spaces as long as wide |
| N. graminea |
| | 2' Leaf sheath junction with blade abrupt, top truncate or rounded, not appendaged (following reliably distinguished only by fruit) |
| |
| | 4. Fruit surface smooth, shiny (finely net-like at 20 × magnification); anthers 1-chambered; stigmas generally 3 |
| N. flexilis |
| | 4' Fruit surface dull, clearly net-like, pitted; anthers 4-chambered; stigmas 2–3 |
| N. guadalupensis
|