1	"Alar cells rectangular and thick-walled; stems plumose and loosely ascending; leaves 3-5 mm long"	2
1	"Alar cells at least in part quadrate or isodiametric; main stem prostrate; leaves smaller"	3
2	"Plants of high-elevation calcareous bogs; older portions of stems densely cloaked with clusters of brown rhizoids that are inserted on the abaxial surface of the leaf near the costa"	"Tomentypnum nitens"
2	"Plants of soil in mesic forests; rhizoids not so densely arranged, inserted on stem"	"Trachybryum megaptilum"
3	"Quadrate alar cells reaching costa; costa with a number of spines closely arranged on the distal portion; costa extending to near the base of the acumen; dry branches not markedly hamate"	"Homalothecium arenarium"
3	"Alar cells not reaching costa; spines on costa inconspicuous, mostly single; length of costa usually shorter; dry branches mostly hamate"	4
4	"Differentiated alar cells quadrate to short-rectangular, up to 15 on margin and 10 along the base; quadrate alar cells extending farther along margin than along immediate inframarginal regions"	5
4	"Differentiated alar cells fewer; immediate margin of alar region with elongate cells"	6
5	"Leaves long-decurrent; main stems up to 15 cm long"	"Homalothecium californicum"
5	"Leaves not or very little decurrent, plant smaller"	"Homalothecium pinnatifidum"
6	"Larger stem leaves often with a somewhat auriculate base; alar cells mostly elongate but with a few quadrate cells; urn 2.4-2.8 mm long with a short-rostrate operculum over l mm long; mostly on trees near the coast"	"Homalothecium fulgescens"
6	"None of the stem or branch leaves at all auriculate; alar cells mostly quadrate; urn shorter with operculum conic and shorter; ecology various"	7
7	"Leaves with several marginal teeth near junction of alar region with more distal region; plant usually very regularly pinnate, often with flagelliform caducous branchlets; stem leaves mostly less than 2 mm long; plant epiphytic on trees near the coast"	"Homalothecium nuttallii"
7	"Leaves without such peribasal teeth; plant pinnate but often obscurely so, without caducous branchlets; stem leaves larger; range and geography various"	8
8	"Alar cells rather obscure under low magnifications of the compound microscope with alar region more opaque than surrounding cell regions"	"Homalothecium nevadense"
8	"Alar cells with outlines clear under low magnigication; alar region not so opaque"	"Homalothecium aeneum"