Plants and Animals

Ammannia robusta Sessile tooth-cup

Key Characteristics

Short, annual forb of moist exposed soil; up to 40 cm tall, stem flushed with red; flowers and fruits mostly sessile, clustered in axils of cordate-based leaves in groups of 1 to 3, calyx with 4 teeth or shallow lobes slightly exceeding the appendages; pale lavender flowers 2.5 to 5.0 mm long. Resembles Rotala ramosior, which has tapered leaf bases and flowers solitary in axils. Specimens of A. robusta have historically been misapplied to A. coccinea, which ranges to the south and west of Michigan and has smaller (2.0 to 3.5 mm long), deep purple flowers.

Status and Rank

US Status: No Status/Not Listed
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G5 - Secure
State Rank: SNR - Not ranked


CountyNumber of OccurrencesYear Last Observed
Allegan 1 2017
Monroe 2 1977
Van Buren 1 2013

Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.


Found in wet or marshy areas with exposed soil such as mudflats, sometimes in floodplains. Often found in cultivated soil (e.g., on the margins of farm fields in low-lying areas).

Natural Community Types

For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.

Associated Plants

The limited data on associates for this species in Michigan includes brook nut sedge (Cyperus bipartitus), scouring rush (Equistem hyemale), and softstem bulrush (Schoenoplectus tabernaemontani). Associates in a floodplain in Iowa include water-hemp (Amaranthus tuberculathus), horseweed (Conyza canadensis), long-scaled nut sedge (Cyperus strigosus), spike rush (Eleocharis obtusa), cut grass (Leersia oryzoides), false pimpernel (Lindernia dubia), tooth-cup (Rotala ramosior), frost aster (Symphyotrichum pilosum), and neckweed (Veronica peregrina).

Management Recommendations

Maintain hydrological fluctuations. This species requires soil disturbance, especially due to flooding and associated drawdowns, and thrives in bare soil that is moist or saturated. The persistence of this species may depend on recruitment from the seed bank under favorable conditions (i.e., water drawdown).

Survey Methods

Random meander search covers areas that appear likely to have rare taxa, based on habitat and the judgment of the investigator.

  • Meander search

    • Survey Period: From third week of August to fourth week of October


Survey References

  • Elzinga, C.L., D.W. Salzer, and J.W. Willoughby. 1998. Measuring and Monitoring Plant Populations. The Nature Conservancy and Bureau of Land Management, Denver. BLM Technical Reference 1730-1. 477pp.
  • Goff, G.F., G.A. Dawson, and J.J. Rochow. 1982. Site examination for Threatened and Endangered plant species. Environmental Management 6(4): 307-316
  • Nelson, J.R. 1984. Rare Plant Field Survey Guidelines. In: J.P. Smith and R. York. Inventory of rare and endangered vascular plants of California. 3rd Ed. California Native Plant Society, Berkeley. 174pp.
  • Nelson, J.R. 1986. Rare Plant Surveys: Techniques For Impact Assessment. Natural Areas Journal 5(3):18-30.
  • Nelson, J.R. 1987. Rare Plant Surveys: Techniques for Impact Assessment. In: Conservation and management of rare and endangered plants. Ed. T.S. Elias. California Native Plant Society, Sacramento. 8pp.

Technical References

  • Gleason, H. A., and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. Second edition. The New York Botanical Garden, Bronx. 910pp.
  • Graham, S.A. 1979. The origin of Ammannia x coccinea Rottboell. Taxon, 28(1): 169–178.
  • Graham. S.A. 1985. A revision of Ammannia (Lythraceae) in the western hemisphere. Journal of the Arnold Arboretum, 66(4): 395–420.
  • Gray, A. 1950. Gray's Manual of Botany; eighth ed. Van Nostrand Reinghold, New York. 1632pp.
  • Holmgren, N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the vascular plants of Northeastern United States and adjacent Canada. New York Botanical Garden, Bronx. 937pp.
  • van der Valk, A.G. 2013. Seed banks of drained floodplain, drained palustrine, and undrained wetlands in Iowa, USA. Wetlands 33(1): 183–190.
  • Voss, E.G., and A.A. Reznicek. 2012. Field Manual of Michigan Flora. University of Michigan Press, Ann Arbor, MI. 1008 pp.