Nasturtium officinale Watercress is an aquatic or semi-aquatic perennial herb with bright white flowers that resemble the shape of a cross; hence, an old name (Cruciferae) for the mustard family, to which watercress belongs. Watercress is commonly found in cold, alkaline waters of springs, spring runs, and similar streams throughout the State of Missouri, as well as the majority of the North American continent. Watercress is also worldwide in distribution and is usually considered an introduced species in North and South America, Australia, South Africa and New Zealand. Watercress is a hardy perennial, with creeping, hollow, fleshy, square stems to 30-50cm with many side stems of lush-green, oblong-ovate leaves. Very small, white flowers with four-petalled corollas resembling a Greek cross, which is a characteristic of plants in the Brassicaceae family (syn. Cruciferae family, the name coming from Latin meaning to bear a cross, because of the cross-like resemblance of the flower).Watercress is a member of the mustard family, which includes many well-known leafy and tuberous vegetables such as collard greens, kale, turnips, and radishes, as well as many problematic weeds such as garlic mustard
Watercress - fs.fed.us, https://www.fs.fed.us/wildflowers/plant-of-the-week/nasturtium_officinale.shtml (accessed January 19, 2017).
Free herb information - WATERCRESS - Herbs are Special, http://www.herbsarespecial.com.au/free-herb-information/watercress.html (accessed January 19, 2017).