Key to the species of Korthalsella

1Flowers in terete spicate conflorescences which arise singly or in threes, terminally and laterally, these sharply distinct from the strongly flattened vegetative cladodes
1'Flowers produced at nearly all nodes, or predominantly on more slender lateral cladodes, but not in strongly differentiated spicate conflorescences (the internodes of flowering branches showing a gradual rather than an abrupt transition in shape from the lower non-flowering ones)
2Flowers 3 in each cluster; conflorescences commonly lateral, sometimes terminal; conflorescence internodes 1-1.5 mm long
2'Flowers 40 or more in each cluster; conflorescences rarely lateral, mostly terminal; conflorescence internodes 1.5-7 mm long
3Internodes terete, without visible veins; plants very slender, up to 3 cm long; hosts conifers
3'Internodes compressed or flattened in one plane, with 1-3 veins visible as raised ribs; plants slender to robust, mostly more than 5 cm long; hosts dicotyledons
4Largest internodes usually 1-ribbed, 5-12 mm long; plants mostly less than 10 cm long; flowers usually 8 or fewer in each cluster
4'Largest internodes usually 3-ribbed, 10-27 mm long; plants mostly more than 10 cm long; flowers usually more than 10 in each cluster