Plant species matter!
Blue porterweed (Stachytarpheta jamaicensis) is native to Florida, according the Florida Plant Atlas. Nettleleaf velvetberry (Stachytarpheta cayennensis) is listed as a category #2 invasive pest plant by the Florida Exotic Pest Plant Council (FLEPP) and was, until recently, labeled Stachytarpheta urticifolia. Lisa Earnest (Class of 2016) asked about how to differentiate between the native wildflower and the invasive pest plant.
Blue porterweed is a low growing (no taller than 18″) and sprawling plant with horizontal stems. Its leaves are coarsely serrate with obtuse teeth generally pointing toward leaf tip. Its leaves are shown in the first picture. Note that there are NO prominent raised areas between leaf veins.
By contrast, nettleleaf welvetberry is a distinct woody trunk and grows to be 4 – 6′ tall. Its leaves are wrinkly and crinkly with a “quilted” appearance (bullate). Its marginal teeth are more numerous, more acute, and tend to point outward. Its leaves are shown in the second picture.
The flowers of blue porterweed are bluish in color and are held on long spikes that can be up to 12″ long and sometimes flop over.
The flower of nettleleaf velvetberry are more purple or violet in color and are held on narrower, more erect spikes.
Blue porterweed may have been brought to Florida by aboriginal people from the Caribbean for medicinal use. A beer-like drink or “porter” can be brewed from its leaves. It is the larval host plant for tropical buckeye (Junonia genoveva) butterflies.
The exotic, but similar, nettleleaf velvetberry is Asian in origin. These two species have hybridized, and the hybrids are recognized as S. x intercedens. They are usually 2-3′ and trunked. Likely, the plant pictured below growing at the Florida Medical Entomology Laboratory is a hybrid.
Both of these porterWEEDS are excellent nectar sources for butterflies and “volunteer” readily. Some folks would call both of the weedy. Please try to plant the only the native species in your garden.
Visit the website of the PInellas Chapter of the Florida Native Plant Society to read a much more detailed account of porter weeds by Naturalist Roger Hammer.