Porterweed (Stachytarpheta) at Bok Tower Gardens
Stachytarpheta is a large genus of predominantly Neotropical herbs and shrubs in the vervain family (Verbenaceae). Collectively referred to as porterweeds, the genus name derives from the Greek ‘stachys’, meaning spike and ‘tarphys,’ meaning thick and alludes to the thick, often elongate inflorescence upon which the flowers are borne.
Blue Porterweed growing in Hammock Hollow
Depending upon the species, flowers vary from blue to purple, or occasionally red (rarely white), and produce copious nectar that attracts hummingbirds and numerous butterfly species. Combined with their ornamental appeal and relatively carefree culture, Stachytarpheta have become popular landscape plants in many warm temperate and tropical regions of the world. Bok Tower Gardens features three species of porterweed: blue porterweed (Stachytarpheta jamaicensis), nettle-leaf porterweed (Stachytarpheta cayennensis) and coral porterweed (Stachytarpheta mutabilis).
Blue Porterweed (Stachytarpheta jamaicensis)
Blue porterweed is a short-lived, herbaceous perennial found throughout the Caribbean, Mesoamerica, and northern South America. It is also the only species of Stachytarpheta native to the United States, where it occurs only in the southern half of the Florida peninsula. At home in coastal environments, particularly on dunes or over shell middens, the species is also found further inland along roadsides or in sandy pastures or other disturbed environments.
Blue porterweed is a low-growing species reaching 1-2 feet in height, with a 3-4 foot spread. This low, spreading growth habit makes for a beautiful groundcover or colorful addition to a sunny, perennial border. In cultivation, the species grows on a variety of soil types but performs best on well-drained soils where it may benefit from supplemental irrigation during prolonged periods of drought. The blue to purple or lilac flowers and are borne in succession along prominent one-two foot spikes that extend above the foliage. Flowering typically occurs in summer but can occur year-round in warmer climates. Plants take full sun or part shade and grow reliably in USDA zone 9 or above. This beautiful, little native species deserves to be more widely planted, but unfortunately, many nurseries mistakenly sell the exotic nettle-leaf porterweed in its place.
Nettle-leaf Porterweed (Stachytarpheta cayennensis)
Nettle-leaf porterweed (Stachytarpheta cayennensis) is native to Mesoamerica and the Caribbean, south to Argentina and Paraguay where it grows in grasslands, savannas and a variety of forested situations. The species is an upright, suffrutescent (i.e., with a woody base) herb or subshrub reaching ca. 6 feet in height and features small, dark purple flowers borne on numerous, slender flower spikes. A prolific bloomer, nettle-leaf porterweed is popular in cultivation and is now naturalized in tropical regions throughout the world, including Africa, Melanesia and Australia. In Florida, it is listed by the Florida Exotic Plant Pest Council as a category II invasive species for the southern portion of the state. The species is occasionally sold under the synonymous name Stachytarpheta urticifolia, and can be distinguished from our native blue porterweed by its upright habit and larger overall size.
Cultural requirements are similar to those of our native porterweed and plants benefit from well-drained soils and full sun, but will also tolerate a variety of soil types and moisture regimes including moderate drought. Although useful as a hedge or foundation planting, we cannot recommend this species for central and southern Florida as it hybridizes readily with our native blue porterweed, and can aggressively self-seed under ideal garden conditions. Although we have not observed this species exhibiting invasive behavior at Bok Tower Gardens, we closely monitor our plantings and have been removing many of them recently in favor of our native blue porterweed. For those interested in a larger, but more well-behaved species, we suggest coral porterweed.
Coral Porterweed (Stachytarpheta mutabilis)Coral Porterweed
Coral porterweed (Stachytarpheta mutabilis) is a neotropical species found in humid forests, woodlands and ruderal areas from southern Mexico to Colombia and into parts of the Caribbean. This suffrutescent herb or subshrub can reach 6 feet (or more) in height with a similar spread and possesses a slightly more coarse texture than its nettle-leaved cousin. Coral porterweed is also widely cultivated and naturalized in parts of the old world tropics but has not yet demonstrated any significant invasive tendencies in Florida.
Coral Porterweed prefers moist, well-drained soils and full sun, but is widely adaptable to a variety of soil types and moderately drought tolerant once established. In tropical climates, plants bear pinkish-red or coral flowers on 1-2 foot spikes year-round; however, in more temperate locations (including central Florida), expect flowering in mid-summer through fall and into early winter. Plants are Ideal for pollinator gardens and make excellent natural screens or hedges. Hardy to USDA zone 9a, coral porterweed is a dieback shrub in north Florida; however, in the southern half of the state where plants survive year-round, pruning in late winter will help maintain a shapely appearance.
Nettle-leaf Porterweed with pollinator
Blog was written by Patrick Lynch, Plant Records Curator, and photographed by Cassidy Jones, Social Media Coordinator.