Key to the species of Hypnea

1	Plants less than 5 cm high, in mats or cushions	2
1	Plants more than 5 cm high, loosely tangled or free	3
2	Axes and branches less than 400 µm in diam., branching dichotomous and close; webbing between branches common	*H. spinella* (C. Agardh) Kützing
2	Axes and branches mostly 600-1000 µm in diam., linked by secondary attachments into dense mat or clump	*H. pannosa* J.Agardh
3	Plants without percurrent primary axes, branching broadly dichotomous, with both sides of dichotomy symmetrically divided	*H. cervicornis* J. Agardh
3	Plants with percurrent axes	4
4	Apices of many axes and branches with widened hooked or curved ends	*H. musciformis* (Wulfen) Lamouroux
4	Apices straight, not broadened and hooked	5
5	Primary axes and main branches distinct, with short spinous branchlets radially attached	*H. valentiae* (Turner) Montagne
5	Primary axes usually unbranched, covered by narrow, soft branchlets of various lengths	*H. chordacea* Kützing