Beware the perils of creeping indigo

The term creeping has many negative implications. It conveys sneaky behavior with potentially malevolent intent; to pursue or follow someone in a persistent, secretive way. By doing so, the goal is to advance gradually and unnoticed, then infringe on some aspects of the target’s existence. Leon County’s botanical population, both native and exotic, is under threat daily from a creeping plant.

Creeping indigo (Indigofera spicata) is a weed with many traits equivalent to a malicious stalker whose sole purpose is to conquer territory and supplant the current inhabitants. This commonly overlooked exotic invader does not get the attention of the long list of infamous invasive plants such as kudzu, cogon grass, and climbing fern.

A native of Africa, this plant is a legume. Most legumes are viewed favorably by the agricultural community since they possess nitrogen-fixing bacteria in their root nodules.

Creeping indigo was introduced from Ceylon to Gainesville, Florida, around 1925 as part of a research project to investigate several properties including nitrogen fixation and its potential as a forage crop for the livestock industry.

While this species was considered to have a good nitrogen fixing capacity, there were other features which were not appreciated. Livestock toxicity issues began to be a concern of researchers as early as 1933.

Historically, most of the Indigofera species were used for production of indigo dye which resulted in deep blue shades in a variety of textiles. Over time this stable dye became a valuable commodity and was hauled by way of pack animals to distant locations for barter in ancient markets and bazaars.

Creeping indigo does not contain as much dye as other species in its genus and was ignored as a valueless weed until the early 20th century. Legumes such as clovers and peanut hay make excellent forage, but there is a constant search for the next improved option.

When early tests as potential forage were conducted on rabbits, one did not survive the initial grazing trial. The surviving rabbit recovered after creeping indigo was removed from the diet. Besides rabbits, equine, cattle, sheep, goats, guinea pigs, and birds have also been poisoned by this exotic plant.

Swine, demonstrating exceptionally good sense, will not eat creeping indigo and have avoided it in feeding tests.

Identification of creeping indigo in the autumn is aided by the very distinctive seed pod clusters. Seed pods are straight and approximately an inch long in densely packed groups of about one hundred pods per stalk. The downward-pointing clusters are bright green when immature, but dry to a matte black. The pods easily shatter when bumped or struck by an animal and will scatter the tiny seeds within.

During the growing season, creeping indigo is a low growing plant which lies over in a prostrate fashion, potentially reaching six feet in length. Leaves contain seven to nine hairy leaflets and stems are hairy, too.

Flowers of creeping indigo appear at the base of the leaves in the summer and contain numerous pinkish to salmon colored blooms. It can grow in urban and rural environments, so as the weather heats up, keep an eye out for the sprawling low growth of its stems and leaflets and emerging flowers. Soon after those pretty flowers disappear and seed pods emerge, this creeping beauty becomes everyone’s nightmare.

Les Harrison is the Extension Director and Agriculture and Natural Resources Agent for UF/IFAS Extension Wakulla County, an Equal Opportunity Institution. For gardening questions, email the Leon County extension office at AskAMasterGardener@ifas.ufl.edu.