Variegated Water Parsley;
aka, Rainbow Water Celery;
aka, "Flamingo" Silom, Selom, or Seri;
aka, Java Dropwort
I obtained this plant from an Asian woman who told me it was a type of watercress her family ate in Korea. I puzzled over whether it could really be some kind of cress until I discovered she actually meant water celery, also known as water parsley.
This is specifically a variegated form called Oenanthe javanica "Flamingo" (formerly known as O. stolonifera), native to Asia & Australia. The commonly cultivated variegated form "Flamingo" is a bit smaller than the species, & less invasive, though it certainly can spread like crazy until it reaches dry ground. It does well in regular garden soil kept moderately moist, but will also thrive at pond margins, or partially submerged in water.
It's chief feature is the colorful serated leaves of cream, green, & pink, but in summer it also has small white carrot-flower umbrels. It grows to about six inches tall, sometimes more than a foot tall, with pracatically limitless spread via rhizomes. If it happens to spread to far, it is not difficult to pull from where it isn't wanted. It's hardy to about 15 degrees F., & in mild climates can be at least partially evergreen. It prefers partial shade, but ours gets full morning sun which does not seem to harm it so long as there is always some moisture around it.
Lovely as a garden ornamental, it also happens to be very good to eat, whether fresh on salads or sandwiches, or cooked in soups or stuffings, or merely as an especially pretty garnish. Young leaves taste like a mild celery; older leaves are spicier & may be nicer steamed with vegetables than raw. Since it grows so vigorously, it's a good idea to really make the effort to use some of it in the kitchen.
The leaves can also be dried for later use as a tea, regarded in Malaysia & elsewhere as having medicinal antioxidant or health-tonic properties. Its curative value is mentioned in ancient or classical Chinese herbal texts. Although many herbal medicines have no measurable effect beyond that of a placebo, there is some science conducted on rats by Jong-Cheol Park et al (1996) indicating possibly healthful responses to persicarin extract & other components of O. javanica.