The So-called Porterweeds, by Roger Hammer, Reprinted from the Miami-Dade Chapter's newsletter, The Tillandsia, Jul.–Aug. 1994
Editor’s note: Since this article was published, Stachytarpheta urticifolia has been reclassifed as Stachytarpheta cayennesis.
The genus Stachytarpheta is comprised of 65 species of annual herbs or low, perennial shrubs mostly of the New World tropics but also with representatives in southeast Asia and on Pacific Islands. They are members of the well-known Verbena Family, or Verbenaceae, and are highly regarded as butterfly attractors. In the tropical Americas, they attract hummingbirds as well. It is for this very reason why many species have found their way into cultivation in tropical and warm temperate regions of the world.
Throughout the Caribbean, and in Florida, these plants are commonly called porterweeds in reference to the medicinal properties bestowed upon them. A foaming, porter-like brew, much like beer, is made from at least one species in the Bahamas. This concoction is used as a drink for fever, for "the cooling of the blood," as a wash for skin irritations, to relieve constipation and for worms in children. Whether it works or not is open to conjecture. Other local names include "snakeweed," "rat's tail" and "vervain." The generic name is taken from the Greek stachys, meaning "spike," and tarphys, meaning "thick," referring to the thickened flowerspike typical of the genus.
There are no recent monographs of this genus, which has resulted in a plethora of misapplied names in areas where they are cultivated or naturalized. Plants offered in many Florida nurseries and garden shops are either mislabeled or sold under names with no botanical standing. This adds to the taxonomic confusion surrounding the genus. There is but a single species native, or presumably native, to Florida, and that is Jamaica porterweed, Stachytarpheta jamaicensis, sometimes referred to as "blue porterweed." This is a sub-shrub growing to a typical height of only one or two feet with a sprawling or decumbent habit. It often forms a dense mound of stems in cultivation. Leaves are dull, light green or gray-green, although some plants may be entirely blushed with purple. The leaf margins are coarsely serrate and the teeth are generally forward-pointing (towards the leaf tip). The leaves are usually glabrous (smooth) above, but may also be pilose (slightly hairy) on the lower surface, and there are no prominent raised areas between the leaf veins. One to several small, blue flowers are borne on green, quill-like spikes. With each passing day, flowers appear slowly up the stem, but each flower lasts only a single day.
Jamaica porterweed is generally considered to be a Florida native, although some botanists believe that this species arrived in Florida along with early Bahamian settlers who brought seeds of medicinal plants with them. This is a species of roadsides and other disturbed sites, seldom being found in undisturbed native plant communities.
All other species of the genus found in Florida are clearly exotic. The most prominent species that is fast becoming established as an escaped exotic in southern and central Florida is Stachytarpheta urticifolia (or S. urticaefoli). This a four- to six-foot woody shrub with violet to purple flowers that, like the flowers of S. jamaicensis, only last a single day. A flowering specimen is quite attractive and is an excellent butterfly attractor. There is a highly-prized white-flowered form (forma albiflora) cultivated on Guadaloupe and Martinique in the Lesser Antilles. Leaves are dark green, somewhat glossy, with acute, marginal teeth that are more numerous and outward-pointing with S. jamaicensis. When comparing these two species, look closely at the leaves and growth habit. The leaves of S. urticifolia have distinct raised areas between the leaf veins, giving the leaf a quilted (bullate) appearance. Growth habits are entirely different; S. jamaicensis is always low and sprawling, while S. urticifolia forms an upright woody shrub with a distinct trunk. S. urticifolia is native to tropical Asia.
Native plant nurseries in central and southern Florida should ensure that they are only offering Stachytarpheta jamaicensis, Jamaica porterweed.
Hopefully, a modern monograph of this genus will help us better understand this interesting group of plants, the so-called porterweeds.
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Porterweeds Revisited, by Roger Hammer, Reprinted from The Tillandsia (date unknown)
It recently came to my attention that certain FNPS chapters are continuing to sell the nonnative species of porterweeds (Stachytarpheta spp.) at their plant sales. So I thought that I should revisit this group of plants in case there is still some misunderstanding out there in Native Plant Land. Telling the native species from the exotic species isn't all that difficult. Our native blue porterweed, Stachytarpheta jamaicensis, is a low-growing plant with branches that typically spread horizontally, forming a short central stem. The height of the plant, not counting the bloom spikes, averages about 10" high, sometimes mounding. The leaves are coarsely toothed and the teeth generally point toward the tip. The leaves are dull green or sometimes with a purplish blush. Small blue flowers are produced either singly or 2-3 in a cluster on a thickened spike to 12" long or more, somewhat resembling a rat's tail. It is called "rat tail" in the Bahamas. Individual flowers last a single day.
A commonly cultivated exotic species, and one that is often touted as native to Florida, is nettleleaf vervain, Stachytarpheta urticifolia. It is native to tropical Asia. Nearly all other species are from the Americas. This plant has an upright, shrubby growth habit to about 5' tall. The leaves are dark green, more finely toothed than our native species, and the teeth are more numerous and outward-pointing. The leaves also have a distinct quilted appearance on the upper surface. The flower spikes are narrower than on S. jamaicensis; the flowers are slightly smaller and are distinctly darker blue with a white center. Individual flowers last a single day.
Another commonly cultivated species is pink porterweed, Stachytarpheta mutabilis, a native of South America. This species has a shrubby, somewhat sprawling growth habit to about 7' tall. It has light green pubescent leaves that are larger than the previous two species, ranging to about 4" long and 2" wide. The thick flower spikes bear 3-12 or more light pink to bright rosy pink flowers that last for several days each. There is also a violet-flowered variety of S. mutabilis called var. violacea and both have even made it into the garden shops of Home Depot and KMart.
Here's a big part of the problem: In the book The Guide to Florida Wildflowers by Walter Kingsley Taylor (Taylor Publishing Company, Dallas, TX, 1992), the photo that accompanies the description for blue porterweed, Stachytarpheta jamaicensis, is actually S. urticifolia, the exotic species. In the recently published book Your Florida Guide to Butterfly Gardening: A Guide for the Deep South by Jaret C. Daniels (University Press of Florida, Gainesville, FL, 2000), there is a photo labeled "Porter Weed" and the photo is correctly identified as Stachytarpheta urticifolia. I thought that someone had finally gotten it right until I read the text that states, perennial, native, cultivar. I don't know where the author got the cultivar part because this is not a cultivated variety. And, as stated before, it's not native; it's an exotic species from tropical Asia.
To make matters worse, there are hybrids of our native S. jamaicensis and the exotic S. urticifolia. The hybrid looks similar to S. jamaicensis but has an upright growth habit from 2' to 3' tall. This hybrid is called S. x intercedens, and it does occur in Florida, especially where the two parents grow in close proximity to each other. Just what we need.