Occurrence of endodermis with a casparian strip in stem and leaf

It is well known that an endodermis with casparian strip always occurs in roots, but few people are aware that it also occurs in stems and leaves of some vascular plants. The rather sparse literature on endodermis in aerial organs was last included in a review in 1943. The present compilation, which does not consider hydathodes, nectaries, or other secretory structures, emphasizes distribution of cauline and foliar endodermis with casparian strip. It occurs unevenly among major taxa: quite common in rhizomes and leaves among pteridophyte groups, with exceptions; absent in gymnosperm stems but found in leaves at least among some conifers; in stems of at least 30 mostly herbaceous angiosperm families, but far less common in leaves, where it is mostly reported from petioles. Etiolation can induce casparian strips in stems and petioles of some herbaceous plants, but results from leaf blades are questionable. There are recent reports of an endodermis with casparian strip in leaves of both woody and herbaceous taxa. The physiological function, if any, of a casparian strip in aerial organs remains unknown.