Key to the common 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

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