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Montana Field Guide

Montana Field Guides

Toothcup - Rotala ramosior

Species of Concern

Global Rank: G5
State Rank: S1S2
* (see State Rank Reason below)

Agency Status
MNPS Threat Rank: 4
C-value: 6

External Links

State Rank Reason (see State Rank above)
Rare in Montana, where it is known from approximately a half-dozen wetland sites in the valley bottoms in the western portion of the state. Potential threats and impacts to the known occurrences, as well as population trends, need to be evaluated.
General Description
Toothcup is a small, glabrous annual with simple or branched, erect to prostrate stems that are up to 10 cm high. The opposite, narrowly lance-shaped leaves have short petioles and are 15-30 mm long. The tiny, solitary flowers are sessile in the axils of upper leaves. The cup-shaped, shallowly 4-lobed calyx is 1-3 mm long in flower but up to 4 mm long in fruit. The 4 stamens are shorter than the 1 mm long, white petals. The fruit is a globose capsule that is ca. 3 mm across.

Flowering in late July-August.

Diagnostic Characteristics
Ammannia robusta has sessile, clasping leaf bases. Members of the genus Gratiola (Plantaginaceae) have short-stalked flowers and separate sepals. A hand lens will be necessary to discern the flower characters.

Species Range

Range Comments
Throughout U.S. south to S. America (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Summary of Observations Submitted for Montana
Number of Observations: 26

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Open, wet, gravelly soil around ponds and sloughs in the valley zone.

Ecological Systems Associated with this Species

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Citation for data on this website:
Toothcup — Rotala ramosior.  Montana Field Guide.  .  Retrieved on , from