BC Conservation Data Centre: Species Summary
Callitriche marginata
winged water-starwort
| Scientific Name: | Callitriche marginata Torr. | ||||||||||
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| Scientific Name Synonyms: |
Callitriche longipedunculata
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| English Name: | winged water-starwort | ||||||||||
| 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: | CALLMAR | ||||||||||
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| Conservation Status / Legal Designation | |||||||||||
| Global Status: | G4 (Aug 2023) | ||||||||||
| Provincial Status: | S3S4 (Apr 2019) | ||||||||||
| BC List: | Yellow | ||||||||||
| Provincial FRPA list: | |||||||||||
| Provincial Wildlife Act: | |||||||||||
| COSEWIC Status: | |||||||||||
| SARA Schedule: | |||||||||||
| General Status Canada: | 2 - May be at risk (2010) | ||||||||||
| Ecology & Life History | |||||||||||
| General Description: | |||||||||||
| Technical Description: | |||||||||||
| Subspecies Comments: | No subspecies of Callitriche marginata are recognized in B.C. | ||||||||||
| Identification Comments: | Callitriche marginata is a small (5-10 cm), limp-stemmed, amphibious annual herb of vernal pools. Leaves are small (< 1 cm), narrow to egg-shaped, and oppositely arranged, and leaf bases are joined by a tiny winged ridge. Submerged leaves are linear, single-nerved, and slightly notched terminally, while aerial leaves are wider and incompletely three-nerved. Tiny flowers are produced on aerial stems in leaf axils. Flowers are apetalous, and are male or female, with or without tiny brown linear bracts. Female flowers have distinct stalks that are much longer than the fruits; styles are sharply reflexed. Aerial elongating stems root at the nodes (under optimal conditions), producing large foliar mats of many interconnected stems. Fruits are achene-like. Four fruits are produced, and each is one-seeded, conspicuously wing-margined, oval, and irregularly pitted in a fine network (Douglas et al. 1998b; M. Miller, pers. comm. 2008). | ||||||||||
| Similar Species: | There are five Callitriche species in southern B.C. that may be confused with C. marginata: C. anceps, C. hermatophroditica, C. heterophylla ssp. bolanderi, C. stagnalis, and C. verna. The five species are very similar morphologically, but only C. marginata produces female flowers with distinct stalks that are longer than the fruit; styles are also sharply reflexed (Douglas et al. 1998b; M. Miller, pers. comm. 2008). | ||||||||||
| Provincial Reproduction Comments: | Asexual reproduction in Callitriche marginata has not been studied but may be common. In the genus Callitriche, new plants can form when a node of an aerial stem comes in contact with a minute part of an adjacent internode (Sculthorpe 1967 in M. Miller, pers. comm. 2008). As an annual plant, the persistence of the population is dependent on sexual reproduction. Flowers are monecious (separate female and male flowers occur on one plant) and lack petals. Pollination systems in Callitriche have been very well studied. Aerial pollination (anemonphily) occurs in C. marginata and is primarily geitonogamous (among flowers on one plant). Self-fertilization occurs when a style of a female flower contacts a dehisced anther from a male flower or when pollen falls from the anther onto the stigma (Philbrick and Anderson 1992 in M. Miller, pers. comm. 2008). Pollinator-mediated fertilization may be rare. When C. marginata was grown under pollinator-free conditions in the greenhouse, seed set was always near 100% (Philbrick and Anderson 1992 in M. Miller, pers. comm. 2008). When cross-pollination occurs, the lack of a perianth or obvious pollinator reward suggests that abiotic (e.g., wind) vs. biotic pollination vectors are involved. Each flower produces four, tiny, one-seeded nutlets. Fertility rates have not been studied, but M. Miller (pers. comm. 2008) observed high rates of reproduction with most individual plants bearing two or more fruit. Genetic variation among populations and subpopulations has not been studied in B.C. The level of gene flow may be low and genetic differentiation among populations and subpopulations may be high over short distances, which is the case for other vernal pool species (Miller 2001). The genetic distinctness of B.C. populations from more southerly populations has not been tested. The closest populations in Oregon are found in inland vernal pools and likely are adapted to very different environmental conditions than B.C. populations. Genetic studies may find that distinct ecotypes have evolved in B.C. and Oregon (M. Miller, pers. comm. 2008). | ||||||||||
| Provincial Ecology Comments: | Callitriche marginata is highly specialized ecologically. It occurs in seasonally ephemeral wetlands (vernal pools/ depressions and seasonally flooded fields) and is likely ill adapted to major structural and hydrological changes to its habitat (M. Miller, pers. comm. 2008). Specific factors affecting population survival, population age structure, recruitment rate, seedling survival rates, mortality rates, and growth rates of C. marginata are not known (M. Miller, pers. comm. 2008). Year-to-year fluctuations in patterns of establishment, survival, growth, and reproduction have also not been studied. However, a few studies have been done on dispersal capability and germination requirements for C. marginata. It has no innate mechanism of seed dispersal and likely depends on animal vectors such as waterfowl or small mammals (Zedler and Black 1992 in M. Miller, pers. comm. 2008). Seeds and seedlings are buoyant and can float for some time before sinking, and may be dispersed short distances in this way. The scattered distribution of C. marginata in south coastal B.C. suggests that some long distance dispersal occurs, but it is not known how frequently. On the other hand, if populations of C. marginata are relicts of a once broader distribution, then the rate of dispersal may be very low. Seeds exhibit primary dormancy, i.e., seeds are dormant at the time of seed dispersal (McClaughin 1974 in M. Miller, pers. comm. 2008). The number of years that seeds are dormant/viable in the soil before germinating is not known. This may be critical information for determining how resilient the seed bank (population) is to drought and other factors. Germination is dependent on a variety of factors: drying, appropriate temperatures, and timing and length of late autumn rains/flooding. Seeds must experience drying in order for post-maturation loss of dormancy (after-ripening) to occur. High germination rates are common once after-ripening occurs, and at appropriate temperatures. Greenhouse experiments have shown that germination rates were almost 100% at temperatures between 10 and 180C, while no germination occurred at room temperature. Another greenhouse experiment showed that germination rates responded to the timing of the onset of fall rains/flooding as well as the length of inundation. In the study, a delayed rainy season (March) resulted in lower germination rates than an earlier rainy season (January); lower germination was also reported when seeds were kept constantly inundated vs. those kept in moderately moist conditions (Bliss and Zedler 1998 in M. Miller, pers. comm. 2008). Over-shading, over-fertilization (eutrophication), competition from introduced species, and over-grazing by waterfowl have been identified as important factors that pose threats to the persistence of vernal pool species such as C. marginata. The response of C. marginata to natural and human-caused disturbance regimes (e.g., fire and trampling, respectively) or management interventions (e.g., removing invasive species or ex situ propagation of C. marginata) are not known. | ||||||||||
| Habitats: (Type / Subtype / Dependence) |
Agriculture / Cultivated Field / Facultative - frequent use
Other Unique Habitats / Garry Oak Vernal Pool / Facultative - frequent use Other Unique Habitats / Vernal Pools/Seasonal Seeps / Facultative - frequent use |
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| Global Habitat Comments: | This species occurs in floodplain and vernal pools, streams, reservoirs, and lakes generally at elevations less than 1000 meters, but occuring at 1670 meters in San Diego County, California (CCH2 Portal 2023, Lansdown in Flora of North America Editorial Committee 2019). | ||||||||||
| Provincial Habitat Comments: | Until it was discovered in an agricultural field in 2007, Callitriche marginata was thought to be restricted to vernal pools or depressions situated on low-lying, coastal rocky knolls, bluffs, and outcrops within the Garry oak ecosystem (M. Miller, pers. comm. 2008). Vernal pools and depressions in B.C. typically form on relatively level sites underlain by bedrock or an impervious hardpan soil layer, and experience winter and spring inundations followed by complete drying in late spring. The growth and survival of C. marginata is strongly linked to these seasonal changes in hydrological regimes. The temperate Mediterranean climate of SE Vancouver Island is characterized by mild winters and dry warm summers with most of the precipitation falling during the winter months. The habitat of C. marginata occurs within Garry oak ecosystems, part of the drier subzone of the Coastal Douglas-fir biogeoclimatic zone (CDFmm) (Douglas et al. 2002). The Garry oak ecosystem is very restricted in B.C. and has been reduced to less than 5% of its original extent (Fuchs 2001). The distribution of C. marginata is, therefore, narrowly restricted since it occurs in vernal pools/depressions, a rare land feature that experiences unique climatic and hydrological properties, within a very rare ecosystem in southern coastal B.C. Associated plant species include Plagiobothyrus scouleri, Myosurus minimus, Camassia quamash, Gnaphalium palustre, Brodiaea coronaria, Tritelia hyacintha, Ranunculus spp., Eleocharis palustris, Carex lyngbyei, and Carex unilateralis (M. Miller, pers. comm. 2008). | ||||||||||
| Provincial Phenology: (1st half of month/ 2nd half of month) |
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| Provincial Phenology Comments: | The annual life cycle of Callitriche marginata has four main stages: seedlings, juveniles, flowering adults and dormant seeds. The first three life stages require wet conditions (even inundation) (M. Miller, pers. comm. 2008). Seeds spend the dry summer and autumn months embedded in the sediment of depressions or pools. Germination occurs in early winter and is triggered by heavy rains. Plants grow from early winter to spring, maturing as pools begin to dry up again (April or May in B.C.). As the pools dry, pedicels expand and push the seeds into the soil, thus ensuring that they are in sufficiently wet habitat to germinate and grow in the next year. Plants die following seed release (approximately early June). | ||||||||||
| Elevation (m) (min / max): | Provincial: 0 / 25 | ||||||||||
| Known Pests: | |||||||||||
| Pollen Vector: | |||||||||||
| Pollinator: | |||||||||||
| Dispersal: | |||||||||||
| Provincial Inventory | |||||||||||
| Inventory Priority: | |||||||||||
| Ownership of occurrences (Known locations): | Mixed government | ||||||||||
| Inventory Need: | Additional occurrences of Callitriche marginata may be located along remote or infrequently visited coastal areas of southern Vancouver Island and adjacent islands (M. Miller, pers. comm. 2008). Inventories of smaller Gulf Islands and islets between Mitlenatch Island and Victoria, as well as some remoter sections of the Vancouver Island coastline between Victoria and Rocky Point, may result in new element occurrences (A. Ceska, pers. comm. in M. Miller, pers. comm. 2008). The rarity of vernal pools limits the likelihood that many new populations will be found in these areas. | ||||||||||
| Inventory Comments: | M. Miller (pers. comm. 2008) did a thorough search for Callitriche marginata in 2002 and 2003. Additionally, the Garry oak recovery strategy has enabled a concerted inventory of habitats such as vernal pools, preferred habitat for C. marginata, by Miller, B.C. Conservation Data Centre personnel, and other expert botanists in recent years. | ||||||||||
| Economic Attributes | |||||||||||
| Provincial Economic Comments: | No economic uses or ethnobotanical products are known for Callitriche marginata. | ||||||||||
| Distribution | |||||||||||
| Endemic: | N | ||||||||||
| Global Range Comment: | Callitriche marginata occurs in western North America, from southwestern British Columbia in Canada, to Oregon, Idaho, California, and northern Baja California, Mexico. The range extent was estimated to be 870,000 square kilometers using herbarium specimens and photo-based observations documented between 1992 and 2023 (CCH2 Portal 2023, Flora of North America Editorial Committee 2019, GBIF 2023, iNaturalist 2023, Villaseņor 2016). | ||||||||||
| Disjunct, more common elsewhere: | Y | ||||||||||
| Peripheral, major distribution elsewhere: | Y | ||||||||||
| Authors / Contributors | |||||||||||
| Global Information Author: | Nordman, C. (2023). | ||||||||||
| Last Updated: | Aug 21, 2023 | ||||||||||
| Provincial Information Author: | P. Bartemucci and S. Hartwell | ||||||||||
| Last Updated: | Jun 18, 2009 | ||||||||||
| Last Literature Search: | |||||||||||
| References and Related Literature | |||||||||||
CCH2 Portal. 2023. Consortium of California Herbaria. Online. Available: https//:www.cch2.org/portal/index.php (accessed 2023). |
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Flora of North America Editorial Committee (FNA). 2019. Flora of North America north of Mexico. Vol. 17: Magnoliophyta: Tetrachondraceae to Orobanchaceae. Oxford Univ. Press, New York. xxiv + 737 pp. |
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Miller, M. 2001. Stewardship Account for Winged Water Starwort Callitriche marginata. Prepared for the B.C. Conservation Data Centre and the Garry Oak Ecosystems Recovery Team. Sponsored by the Habitat Stewardship Program, Gov. Can. and Nat. Conservancy Can. Victoria, BC. 26 pp. |
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NatureServe. 2004b. Habitat-based plant element occurrence delimitation guidance, 1 October 2004. Available: http://www.natureserve.org/explorer/decision_tree.htm (accessed Mar. 17, 2005). |
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Penny, J.L. 2009. Callitriche marginata Update Report Notes: Saanich Flooded Field Inventories. Conservation Data Centre. Victoria, B.C. 3pp. |
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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: Callitriche marginata. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 5, 2026).