As the garden marches into spring mounds of bright green Oxalis appear.  The twelve inch tall cushions of leaves resembling clover come just in time for St. Patrick’s Day but, despite what an occasional catalog selling Oxalis acetosella may say, Oxalis are not true shamrocks.  Studies from 1892 and 1988 requesting true shamrock samples from Ireland only yielded plants from Trifolium and Medicago, no Oxalis.  The cheery mounds with hot pink tubular flowers at Horsetail Haven are Oxalis violacea or violet wood sorrel.  The genus Oxalis is in the Family Oxalidaceae or wood sorrel family.  There are around 700 members of the species, most native to South America and South Africa.  Most are herbaceous with tubers or bulbs.  The leaves are palmately compound with three leaflets that have a clover like appearance.  The leaves often fold up at night or during stormy weather.  Most members of the genus contain oxalates which give them a bitter, sour taste.

There are two forms of Oxalis that Austin gardeners know way too well.  These are the dark green wood sorrels with yellow flowers that we seem to constantly pull from our gardens and flower beds.  The nomenclature of these two is somewhat controversial but the 1999 edition of Shinners & Mahler’s Flora of North Central Texas treats the pesky mat like grower with purple pigmentation as Oxalis corniculata and the greener more erect grower as Oxalis stricta (syn. Oxalis dillenii).  Refer to that source for an in depth discussion.

Violet wood sorrel is only one of many highly ornamental Oxalis that can be grown in Austin. Oxalis drummondii is another Texas native with lavender colored flowers and deeply lobed crescent shaped leaflets.   Oxalis hedysaroids ‘Rubra’ is a South American native with dark maroon leaves and yellow flowers and Oxalis articulata subsp. rubra from Brazil has pink flowers with dark veins and red spots on the underside of the leaves.  Oxalis usually die back during the summer heat and reappear in late winter.  To keep them evergreen they should be planted in light shade and watered frequently.  Some people consider them invasive, the scaly tubers seem to get transplanted around the yard by accident but Ann Marie loves the cheer they bring to the late winter garden.

Despite the word “sorrel” in the common name of many Oxalis, there is only one species that is considered a good culinary option.  This is Oxalis tuberose, a root vegetable grown in Peru that is commonly called “Oca”.   The leaves of other Oxalis may be safe in small amounts to give a pucker of lemon flavor to salad or soup but large amounts of some have poisoned livestock and individuals with kidney stones, gout and arthritis should avoid foods containing oxalates.

To confuse the issue, there are culinary plants called “sorrel” you can find in herb and vegetable sections of nurseries and catalogs.  These are Rumex species in the Family Polygonaceae.  They do have a couple of things in common with our ornamental wood sorrels.  First, they also contain oxalates that yield a sour, lemony flavor and should be eaten in limited quantities.  Second, they too do best in Texas with light shade and attentive watering.  Finally, there are some species that can best be described as “weeds” and others that are highly desirable in the garden.

First the weeds.  These were the original sorrels that historically were eaten and used medicinally by Egyptians, Romans and Europeans.  Sheep sorrel (Rumex acetosella) and curly dock (Rumex crispus) are the most common and are still eaten as greens today, especially in early spring when the leaves are young and tender.  Some authorities recommend boiling the greens with several changes of water to help reduce the oxalates.  Iron cooking utensils and pans should always be avoided when dealing with sorrel as they can color the sorrel black and give it a metallic taste.   Refer to the Texas A & M broadleaf weed site for information about these plants.

Over time more tasty sorrels with lower levels of oxalates were selected for culinary needs.  The four most common ones are Rumex acetosa often called English or garden sorrel, Rumex scutatus, called French sorrel, Rumex patientia or spinach dock and the highly decorative Rumex sanguineus or blood sorrel.  Rumex acetosa will be the sorrel gardeners encounter most frequently.  It has rosettes of bright green, broad leaves and flower stalks of reddish brown flowers in the summer.  It can be used sparingly in salads and more heavily in soups and cream sauces for fish and veal.

Rumex scutatus can be used the same way as Rumex acetosa but the flavor is more acidic.  It is a low grower forming a mat of shield shaped leaves.  Some references state that it may be hard to eradicate.  A cultivar called ‘Silver Shield’ is reported to be quite attractive.  Rumex patientia is reportedly best used in early spring so the assumption is that it is higher in oxalates but Ann Marie is not familiar with the plant.  Rumex sanguineus has been grown at Horsetail Haven.  It forms rosettes of 3 inch leaves that are bright green with dark maroon stems and veins.  Unlike many variegated plants, it retains its dramatic color even in the summer heat.  It will grow best in Austin when given light shade and frequent watering, but may not survive the worst summers.  It can be used as other sorrels, but the leaves toughen up as the plant ages and Ann Marie just prefers it as an ornamental.

For recipe suggestions using sorrel refer to The Herb Garden Cookbook by Lucinda Hutson and The Herb Society of America’s Essential Guide to Growing and Cooking with Herbs by Katherine Schlosser.