Commelina erecta L.
Basis for Listing
The genus Commelina (dayflowers) has five species in the United States: three perennials and two annuals. One of the perennials is Commelina erecta (slender dayflower), which is sometimes subdivided into three overlapping varieties (Brashier 1966).
In Minnesota, there are only two records of C. erecta. Both are from the same 40 acre (16 ha) area in Wabasha County (Blufflands Subsection). This area is part of a much larger natural area managed by the Minnesota DNR and The Nature Conservancy. The first record is from 1983 and has little accompanying information (just “oak woods”). A subsequent survey in 1996 found about 50 plants and described them as “rare and local” in a dry sand prairie. The area is known to have oak woods, savanna, and sand prairie intricately intermixed. High quality examples of this habitat type are rare in Minnesota (Minnesota's Remaining Native Prairie), and they harbor a disproportionate number of rare plant species. For this reason, botanists tend to seek out these habitats and search them carefully. In spite of this scrutiny, no additional populations of C. erecta have been discovered. Information from other states indicates C. erecta could also be found in habitats associated with dry bluff prairies, talus, or rock outcrops. These types of habitats have also been targeted for botanical searches, without success.
The small size of the Minnesota population and the scarcity of suitable habitat put C. erecta at risk of extirpation from the state; hence, it was listed as endangered in 2013. This species is not only rare and vulnerable in Minnesota, it is listed as threatened in Iowa and special concern in Wisconsin.
Commelina erecta is a perennial, with erect or ascending stems. The leaves are sessile, linear to lanceolate, 5-15 cm (2-6 in.) long, and 0.3-4.0 cm (0.1-1.6 in.) wide, with a pointed tip. Each inflorescence is a cyme enclosed in a spathe; the spathe is a specialized floral structure, which may look something like a clam shell. The spathes are green or sometimes purple, stalked, sometimes strongly falcate (hook shaped), 1.0-2.5 cm (0.4-1.0 in.) long and 0.7-1.5 cm (0.3-0.6 in.) wide, and variously hairy. The flower appears to emerge from the spathe on a stalk (peduncle), 0.5-1.0 cm (0.2-0.4 in.) long. The flowers are either bisexual or male and 1.5-4.0 cm (0.6-1.6 in.) across. They have 3 petals; the lowest petal is minute and white, the other 2 petals are much larger and blue (rarely lavender or white). The seed capsules are 3-locular, 2-valved, and indehiscent. There are 3 brown seeds, 2.4-3.5 mm (0.09-0.14 in.) long (Faden 2000).
In Minnesota, C. erecta has been found only in a dry sand prairie and nearby oak woods, which is perhaps more of a savanna than a woods. The setting is an extensive dune formation associated with the Mississippi River in Wabasha County (Blufflands Subsection). The dune system formed from sand deposited by glacial meltwater originating from the Grantsburg sublobe (late Wisconsin Age, 14,000 years ago).
In Minnesota, dunes are dynamic habitats, with prairie vegetation developing in the dry open areas, and oak-dominated woods or savannas developing where a bit more moisture collects or where natural fire-breaks prevent frequent wildfires.
Based on information from adjacent states, this species might also be found in habitats associated with dry bluff prairies, talus, or rock outcrops. In all cases, the sites would be sunny or only partially shaded, well-drained, and sparsely vegetated.
Biology / Life History
Very little is known about the specific biology and life history of C. erecta. It is clearly a perennial that reproduces only by seed (no rhizomes or root suckers). Each flower lasts for only one day, and they are pollinated by flying insects. We can infer (based on the characteristics of its habitat) that C. erecta is adapted to survive heat stress and moisture stress.
Seeds are released from a dry capsule that remains on the plant. The seeds do not have specialized structures to disperse on air currents or water, nor do frugivores spread them in their droppings. The seeds apparently fall to the ground and are eaten or gathered by small granivores, which may act as both seed predators and seed dispersers.
Conservation / Management
It has been reported (Ruthven et al. 2000) that in Texas, C. erecta increases with dormant season burning but decreases with cattle grazing. However, another study (Hansmire et al. 1988) found fire to have no effect on this species.
It has also been reported (Panigo et al. 2012) that C. erecta can survive and thrive after glyphosate application. Glyphosate is a broad-spectrum systemic herbicide that is especially useful in killing annual broadleaf weeds and grasses. This could prove useful, since the habitat where C. erecta occurs in Minnesota is vulnerable to the rapid invasion of non-native plant species, which could represent a serious management problem.
Before any management is conducted, it is essential to know more about the population of C. erecta. Specifically, how many individual plants occur there, how they are distributed within the habitat, the age or reproductive structure of the population, recruitment and mortality trends, and functional aspects of the plant community in which the population occurs.
Best Time to Search
The phenology of C. erecta is not well known in Minnesota; however, it is believed the flowering period is in July and August. Hence, this may be the best time of year to conduct field searches.
Welby Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Brashier, C. K. 1966. A revision of Commelina (Plum.) L. in the U.S.A. Bulletin of the Torrey Botanical Club 93(1):1-19.
Faden, R. B. 2000. Commelinaceae. Pages 170-197 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 22. Oxford University Press, New York, New York.
Hansmire, J. A., D. L. Drawe, D. B. Wester, and C. M. Britton, 1988. Effect of winter burns on forbs and grasses of the Texas coastal prairie. The Southwestern Naturalist 33(3):333-338.
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.
Minnesota Department of Natural Resources. 2006. Tomorrow's habitat for the wild and rare: An action plan for Minnesota wildlife, comprehensive wildlife conservation strategy. Division of Ecological Services, Minnesota Department of Natural Resources. 297 pp. + appendices.
Minnesota Department of Natural Resources. 2009. Map of Minnesota's remaining native prairie 100 years after the public land survey.
Panigo, E. S., I. M. Dellaferrera, J. M. Acosta, A. G. Bender, J. I. Garetto, and M. G. Perreta. 2012. Glyphosate-induced structural variations in Commelina erecta L. (Commelinaceae). Ecotoxicology and Environmental Safety 76:(2)135-142.
Ruthven, D. C., III, J. F. Gallagher, and D. R. Synatzske. 2000. Effect of fire and grazing on forbs in the western south Texas plains. Southwestern Naturalist 45(2):89-94.