| Galium oresbium Greenm., 1898 |
| Galium orizabense Hemsl., 1879 |
| Galium ovale Ruiz & Pav., 1798 |
| Galium parishii Hilend & J.T. Howell, 1934 |
| Galium pendulum Greenm., 1905 |
| Galium pennellii Dempster, 1978 |
| Galium pilosum Aiton, 1789 |
| Galium pilosum var. pilosum Aiton, 1789 |
| Galium pilosum var. puncticulosum (Michx.) Torr. & A. Gray, 1841 |
| Galium porrigens Dempster, 1974 |
| Galium praetermissum Greenm., 1897 |
| Galium pringlei Greenm., 1898 |
| Galium proliferum A. Gray, 1853 |
| Galium punctatum Pers., 1805 |
| Galium puncticulosum Michx., 1803 |
| Galium rzedowskii Dempster, 1975 |
| Galium seatonii Greenm., 1898 |
| Galium sphagnophilum (Greenm.) Dempster, 1973 |
| Galium sphagnophilum var. mazocarpum (Greenm.) Dempster, 1973 |
| Galium sphagnophilum var. sphagnophilum (Greenm.) Dempster, 1973 |