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BC Conservation Data Centre: Species Summary


Rotala ramosior
toothcup

 
Scientific Name: Rotala ramosior (L.) Koehne
English Name: toothcup
 
Classification / Taxonomy
Scientific Name - Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Classification Level: Species
Species Group: Vascular Plant
Species Code: ROTARAM
Kingdom Phylum Class Order Family
Plantae Anthophyta Dicotyledoneae Myrtales Lythraceae
   
Conservation Status / Legal Designation
Global Status: G5 (May 2023)
Provincial Status: S1 (Apr 2019)
BC List: Red
Provincial FRPA list:   
Provincial Wildlife Act:
COSEWIC Status: Endangered (Nov 2014)
SARA Schedule: 1  -  Endangered (Jun 2003)
General Status Canada: 1 - At Risk (2010)
   
Ecology & Life History
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.
Technical Description: From Field Guide to Colorado's Wetland Plants (Culver and Lemly 2013):
Growth Habit: annual, fibrous-rooted, glabrous herb.
Stems: erect or nearly prostrate, sometimes creeping at base with more erect branches
Leaves: opposite, broadly linear to narrowly elliptic or oblanceolate, tapering to slender base, (0.5)1-3 cm long and 2-5(10) mm wide.
Flowers: mostly (3) 4 (6) -merous, solitary in axils, sessile, subtended by a pair of bracteoles; floral tube 2-3 mm long, and thick-columnar, becoming thickly urceolate (urn-shaped) at maturity; sepals alternating with triangular appendages of nearly the same size; petals white or pink, about 1 mm long, caducous (falling off early).
Fruit: 3- 0r 4-valved capsule, equaling or a little shorter than the floral tube..
Diagnostic Characteristics: Ammania coccinea has sessile, clasping leaf bases. Gratiola have short-stalked flowers and separate sepals. A hand lens will be necessary to discern the flower characters.

From Field Guide to Colorado's Wetland Plants (Culver and Lemly 2013):
Main Characteristics:
·Annual herb with 4 petals, white or pink
·Flowers solitary in axils
·Leaves opposite and arranged at right angles to leaf pair above and below, tapered to petioles
Subspecies Comments: None.
Identification Comments: This is a small glabrous annual herb from spreading roots (Douglas et al. 1999; Washington Natural Heritage Program 2005.) Leaves are opposite and taper to a distinct petiole. The white flowers are bell-shaped and sessile (Washington Natural Heritage Program 2005).
Similar Species: This species shares its habitat with Ammania robusta, and may be separated from this genus by its white flowers. In Ammania species, flowers range from lavender to scarlet (Washington Natural Heritage Program 2005). Additionally, leaves of Ammania robusta are sessile and clasping at the base while leaves of Rotala ramosior gradually taper to a distinct petiole (Douglas and Oldham 1999). Ammannia robusta has at least some leaf axils with three to five flowers, while Rotala ramosior rarely has more than one flower per leaf axil (Douglas and Oldham 1999).
Global Reproduction Comments: This is an annual plant that produces numerous small seeds, about 0.3 mm long (Godfrey and Wooten 1981).
Provincial Reproduction Comments: Little information is known on the reproductive biology of Rotala ramosior in BC (Douglas and Oldham 1999), although characteristics can be inferred from data gathered in other jurisdictions. Rotala is monoecious, hermaphroditic, and insect-pollinated (though it is primarily self-pollinated) (Shirley Graham, pers. comm. in Mattrick 2001). Flowers are also homostylous. The self-compatibility likely confers some advantage since flowers are inconspicuous, and probably overlooked by pollinators who spend more time visiting showy species (like Lythrum salicaria in eastern United States). Not very many showy plants occur in Rotala habitats in BC (Lythrum salicaria is not yet known from the sites but does occur in the vicinity), but regardless of this, self-pollination ensures a reliable seed set every year whether pollinator activity is favorable or not.

Seed set from single plants is abundant and seeds are small and light, thus, easily dispersed by wind, water and gravity (Cook 1979). The primary means of dispersal is not known, but Shirley Graham (pers. comm. in Mattrick 2001) suggests that it is wind. Since the seeds have inverted epidermal hairs, it is also possible that they get caught in the feet of waterfowl (Shirley Graham, pers. comm.; Carol Baskin, pers. comm.; Margaret Ardwin, pers. comm. all in Mattrick, 2001).
Provincial Ecology Comments: Rotala ramosior life cycle and phenology are tied to water level fluctuations, showing a preference for sites with little competition (Douglas and Oldham 1999). The shoreline at Rotala sites is kept free of competing vegetation by the natural fluctuations in water levels. Without the fluctuations, more aggressive herbaceous and woody species would begin to colonize the habitat currently occupied by R. ramosior (Brownell and Douglas 2004).
Habitats:
(Type / Subtype / Dependence) 		Other Unique Habitats / Vernal Pools/Seasonal Seeps / Facultative - frequent use
Riparian / Riparian Herbaceous / Facultative - frequent use
Riparian / Riparian Shrub / Facultative - frequent use
Wetland / Bog / Facultative - frequent use
Wetland / Fen / Facultative - frequent use
Wetland / Marsh / Facultative - frequent use
Wetland / Swamp / Facultative - frequent use
Global Habitat Comments: This species is found in wet open sites, low places, shores, depressions, ditches, temporary pools, marshes, and rice fields at elevations ranging from 0 to 1900 meters (Godfrey and Wooten 1981, Graham 2022).
Provincial Habitat Comments: In British Columbia, Rotala ramosior is known from moist to dried alkaline lagoons and moist, fluctuating lakeshores in two interior dry valleys (Douglas and Oldham 1999). Timing and amounts of seasonal rainfall, flooding, and degree of water draw-down in the habitats are of critical importance in the lifecycle of this species.

In Kamloops, it occurs in backwaters of the Thompson River, on sandy, exposed banks of a channel. Associated species include Carex kelloggii, Crassula aquatica, Eleocharis acicularis and Potamogeton nodosus. In Osoyoos area, it is associated with Ammannia robusta, Carex sychnocephala, Cyperus erythorhizos, C. squarrosus, Eleocharis acicularis, Marsilea vestita, Phalaris arundinacea, Potentilla anserina, and Schoenoplectus saximontanus.

Little is known of the physical characteristics of the sites in BC, however some of the plants at Osoyoos occur on a gentle SW slope (5-10 percent slope). Beal (1977) found that Rotala ramosior selects habitats with pH level of 6.3 to 7.6 in North Carolina. The pH is not known for the BC sites.
Provincial Phenology:
(1st half of month/
2nd half of month)		 Jul: / Flowering, Fruiting
Aug: Flowering, Fruiting / Flowering, Fruiting
Sep: Flowering, Fruiting / Flowering, Fruiting
Oct: Fruiting / Fruiting
Provincial Phenology Comments: In BC, this species rarely flowers before August, but flowering times range from July to September. In other parts of the range, flowering times are from June or July to October (Mattrick 2001). Fruiting in the eastern United States is late July to Autumn. As flowering followed a similar schedule in BC to eastern United States populations, fruiting may do the same. Timing of phenology will, however, be linked to a given year's seasonal rainfall timing and intensity and water level draw-down.

Studies by Baskin et al. (2002) showed that flooding and temperature controlled dormancy break in seeds of Ammannia coccinea and Rotala ramosior. They showed that seeds absolutely required light for germination, but different flooding (and timing of flooding) and temperature regimes had varying effects on germination success. In their experiments, they found that at maturity in autumn, about 65-100% of Rotala ramosior seeds were dormant and a large proportion of freshly matured seeds did not germinate at any temperature regime. Flooded seeds hit 50% germination 1 month later than seeds that were not flooded at 30/15 and 35/20 degrees Celcius mean daily maximum and minimum temperatures. In terms of optimum conditions for germination, they found that seeds that were treated to the 35/20 degree Celcius temperature cycle in July produced the highest germination (99-100%) for both flooded and unflooded seeds. Flooded seeds of R. ramosior also required lower minimum temperatures for germination than fresh seeds and therefore, fresh seeds showed some evidence of conditional dormancy. Other experiments showed that seeds will germinate in shallow water at 30/15 degrees Celcius with plenty of light. Unless the water is shallow enough, they probably won't germinate due to the light requirement, thereby ensuring that they don't germinate too early before water draw-down when conditions for seedling establishment are favorable.

Carol Baskin (pers. comm. in Mattrick 2001) found that seeds of Rotala ramosior did not germinate if buried too deeply. Sowing seeds at a depth greater than 1 mm prevented germination. Another study conducted by graduate students at the Brown University on seeds of R. ramosior looked at treatments to induce germination (Fite-Wassilak et al. 2001). They looked at fertilization, gibberellic acid, inundation, control, and stratification treatments and found that cold, moist stratification for 21 days followed by long warm day length yielded the highest germination percentages. All treatments, however produced some germination and when combined with stratification showed an increase in the germination percentages.

Baskin et al. (2002) also found that the optimal temperature regime for dormancy break in seeds of R. ramosior was 20 degree C/10 degree C maximum and minimums, but that dormancy break occurred over a range of temperature and conditions. Low oxygen levels also affect dormancy break, probably by enhancing it. The ability of seeds to come out of dormancy during flooding at field temperatures from late autumn to early summer showed that Rotala is well adapted to its habitat with seeds nondormant when mudflats become de-watered in summer in Tennessee-Kentucky, and likely elsewhere too.

Furthermore, Carol Baskin (pers. comm. in Mattrick 2001) has shown that a few Rotala ramosior seeds live up to 10 years in the soil seed bank. On the other hand, she also reports low survivorship in other seeds tested. Seeds were reported to quickly lose viability with as much as 50% of the seed became non-viable in a single year.
Elevation (m) (min / max): Provincial:  280 / 560
Known Pests:
Pollen Vector:
Pollinator:
Dispersal:
   
 
Provincial Inventory
Inventory Priority: B - Strong
Ownership of occurrences (Known locations): Mixed private/government
Inventory Need: Inventory for this species is needed. While its occurrence in BC is so far only reported in lacustrine habitats, in Washington State, it is considered a riverine species (Washington Natural Heritage Program 2005). In addition, Mattrick (2001) indicates that it also occurs in wet woods, fields and ditches elsewhere in its range. Targeted searches of riverine habitats as well as small ponds and alkali lakes, and ditches, throughout the Okanagan, seem warranted. Targeted searching for this species will benefit its equally rare associates such as Ammania robusta. Both species fluctuate in numbers from year to year based on annual climatic variation and associated water levels and may not make appearances in a given year creating additional challenges for inventory efforts. Because of this fluctuation, but also considering possible additional variation in habitat type, populations may have been overlooked over the years. Given its apparent habitat specificity in the south Okanagan, potential habitat maps could be developed for use in directing inventory efforts.
Inventory Comments: A status report was prepared by George Douglas and Mike Oldham (Douglas and Oldham 1999) and the Osoyoos Lake site has been visited repeatedly since 1991. However, It is not known how much additional inventory time was spent searching for this species elsewhere.
 
Economic Attributes
Provincial Economic Comments: No economic uses are known in BC. In some parts of its range (e.g. California) this is considered a weed species. The Global Compendium of Weeds indicates that this is an invasive species that requires quarantine (HEAR 2002).
 
Distribution
Endemic: N
Global Range Comment: Rotala ramosior occurs in temperate and tropical North and South America, from southern British Columbia and Ontario in Canada, the United States, Mexico, Cental America and the Caribbean, to Peru and Brazil. It occurs in much of the eastern United States, from southern New England, to Florida, central Texas and the eastern Great Plains. It occurs in the Central Valley of California and at scattered locations elsewhere in the western United States. It is introduced in Africa, Europe and Asia. The native range extent in the Americas is estimated to be 34 million square kilometers (GBIF 2023, Godfrey and Wooten 1981, Graham 2022).
Disjunct, more common elsewhere: N
Peripheral, major distribution elsewhere: Y
 
Authors / Contributors
Global Information Author: J.M. (1994), rev. C. Nordman (2023).
Last Updated: May 04, 2023
Provincial Information Author: B. Klinkenberg, R. Klinkenberg and J.L. Penny
Last Updated: Jul 27, 2005
Last Literature Search: Jul 27, 2005
   
References and Related Literature
B.C. Ministry of Environment. Recovery Planning in BC. B.C. Minist. Environ. Victoria, BC.
Baskin, Carol C., Jerry M. Baskin and Edward W. Chester. 2002. Effects of flooding and temperature on dormancy break in seeds of the summer annual mudflat species Ammannia coccinea and Rotala ramosior (Lythraceae). Wetlands 22 (4): 661-668.
Beal, E. O. 1977. A Manual of Marsh and Aquatic Vascular Plants of North Carolina with Habitat Data. North Carolina Exp. Stn. Tech. Rep. No. 247. North Carolina State University. Raleigh, North Carolina, USA.
Brownell, V.R. and G.W. Douglas. [2004]. National Recovery Strategy for Toothcup, Rotala ramosior (L.) Koehne. Recovery of Nationally Endangered Wildlife (RENEW). Ottawa, ON. 39 pp. In press.
Coffin, B., and L. Pfannmuller, editors. 1988. Minnesota's endangered flora and fauna. University of Minnesota Press, Minneapolis, Minnesota. 473 pp.
Cook, C. D. K. 1979. A revision of the genus ROTALA (Lythraceae). Boissiera 29:1-?.
Cook, C. D. K. 1979. A revision of the genus ROTALA (Lythraceae). Boissiera 29:1-?.
Culver, D. R. and J. M. Lemly. 2013a. Field Guide to Colorado's Wetland Plants. Colorado Natural Heritage Program. Colorado State University. 694 pp.
Douglas, G.W. 1995d. Status Report on the Toothcup (Rotala ramosior (L.) Koehne in von Matius). Conserv. Data Cent., B.C. Minist. Environ., Lands and Parks, Victoria.
Douglas, G.W., and M.J. Oldham. 1999. Status Report on Toothcup, Rotala ramosior, in Canada. Unpubl. rep. submitted to the Comm. on the Status of Endangered Wildl. in Can. Ottawa. 25pp.
Douglas, G.W., D. Meidinger, and J. Penny. 2002. Rare Native Vascular Plants of British Columbia, 2nd ed. B.C. Conserv. Data Centre, Terrestrial Inf. Branch, Victoria. 358pp.
Douglas, G.W., D. Meidinger, and J. Pojar. eds. 1999. Illustrated Flora of British Columbia, Vol. 3, Dicotyledons (Diapensiaceae through Onagraceae). B.C. Minist. Environ., Lands and Parks, and B.C. Minist. For., Victoria. 423pp.
Douglas, George W. 1999. Status of toothcup in British Columbia. Wildlife Bulletin no. B-94. BC Minist. of Environ. Lands and Parks and Resources Inventory Branch, Victoria, BC.
Douglas, George W., Michael J. Oldham and J.L. Penny. [2008]. Conservation evaluation of Toothcup, Rotala ramosior (Lythraceae), an endangered vascular plant in Canada. Can. Field Nat. In press.
Fite-Wassilak, A., A. Kane, J. Kelley, and A. Leuck. 2001. Germination of the Rare Wetland Species Rotala ramosior (Lythraceae). Unpublished document. Department of Ecology and Evolutionary Biology (contact Dr. Johanna Schmitt, Box G, Brown University, Providence, Rhode Island, USA.
Godfrey, R.K., and J.W. Wooten. 1981. Aquatic and wetland plants of southeastern United States: Dicotyledons. Univ. Georgia Press, Athens. 933 pp.
Graham, S.A. 2022. Flora of North America. Rotala ramosior. Accessed: September 26, 2022. http://floranorthamerica.org/Rotala_ramosior
HEAR. 2002. Information page on Rotala ramosior (L.) Kuhne. A Global Compendium of Weeds. Hawaiian Ecosystems at Risk Project (HEAR). Online. Available: http://www.hear.org/gcw/index.html (Accessed March, 2005).
Mattrick, C. 2001. New England Plant Conservation Program Conservation and Research Plan: Rotala ramosior (L). Koehne. New England Wildflower Soc. 27 pp.
National Toothcup Recovery Team. 2008. Recovery strategy for the toothcup (Rotala ramosior) in British Columbia and Ontario. Prepared for the British Columbia Ministry of Environment, Victoria, BC, and the Ontario Ministry of Natural Resources, Peterborough, ON. 22 pp.
Washington Natural Heritage Program. 2005. Rotala ramosior field guide page. Available: http://www.dnr.wa.gov/nhp/refdesk/fguide/pdf/rotram.pdf. (Accessed May 2005).
 

Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.

Suggested Citation:

B.C. Conservation Data Centre. 2023. Species Summary: Rotala ramosior. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 13, 2026).