All our species have glandular foliage and a prominent sweet balsamic odor.

1. Leaves decurrent (stem with 2 short wings of leaf tissue extending beneath each node); stems (at least on the less tomentose middle and lower internodes) with evident spreading glandular hairs all or mostly 0.3-0.7 mm long.

P. macounii

1. Leaves not decurrent; stems with glandular hairs, if any, at most ca. 0.2 mm long, usually not evident.

2. Stems green, with evident but tiny (ca. 0.2 mm or less) gland-tipped hairs.

P. micradenium

2. Stems with white tomentum, concealing any glands.

P. obtusifolium