Mature fruit is essential for distinguishing our species of Nasturtium, and a number of collections are here not mapped because they are vegetative or their fruits are too immature. Watercress is a well-known edible plant, the foliage used in salads, mixed juices, soups, casseroles, and as a garnish. Specimens of Cardamine pensylvanica growing in water are sometimes misidentified as Nasturtium for the foliage is quite similar, although the former does not make the large massed beds so characteristic of the latter. Such specimens of Cardamine can usually be identified because the stems do not elongate and creep to form mats and by their ascending pedicels bearing straight slender narrow fruits mostly less than 1 mm wide with very finely papillate (not reticulated) seeds; the valves of the fruit are flatter than in Nasturtium, and curl after discharge of the seeds.

1. Fully mature fruits 1.8-2.7 mm wide; seeds in 2 rows under each valve of the fruit, coarsely reticulate, with ca. 25-50 (-60) areolae on each side.

N. officinale

1. Fully mature fruits 1-1.7 mm wide; seeds in one row under each valve of the fruit, minutely reticulate, with ca. (75-) 100-150 (-175) areolae on each side.

N. microphyllum