Geranium Leaf Comparison Chart

The foliage of Geranium species can vary considerably within and across species depending on environmental conditions such as water, temperature, light, soil type, and season. Leaf structure can even vary on the same plant; upper leaves tend to be more finely divided in all species and often differ in shape from the lower leaves. In addition, Geranium foliage is often misidentified as Delphinium, Mallow, Hydrocotyle, or Sidalcea. The Jepson key uses flowers and fruits to differentiate Geranium species. It does not use leaf structure in the key at all, except to differentiate G. bicknellii vs. G. rotundifolium: https://ucjeps.berkeley.edu/eflora/eflora_keys.php?key=9884. It’s difficult, if not impossible, to identify Geranium species from photos of leaves alone, so it's best to leave foliage-only observations at the genus level in iNaturalist.

Peter F. Yeo, in his classic book "Hardy Geraniums" (Timber Press, 1985, p.61) states:
"In all cranesbills there is variation according to the part of the plant on which the leaves are borne and the climatic conditions under which they unfolded, as well as variation between plants on account of their varying genetic constitutions... therefore they should not be relied upon for identification, but used for confirmation."
This book contains illustrations of basal geranium leaves for those who are interested in delving into leaf identification more deeply.

Note: The pictures in this journal posting were taken from iNaturalist photos of flowers and/or fruits of Geranium species that have been verified as Research Grade. I cropped the photos to remove the flowers and fruits, leaving only the leaves and stems.