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Montana Field Guides

Water Awlwort - Subularia aquatica

Native Species

Global Rank: G5
State Rank: SNR
(see State Rank Reason below)

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State Rank Reason (see State Rank above)
Subularia aquatica is a native aquatic plant in North America where it grows sparsely in the greater Pacific Northwest region (Al-Shehbaz in Flora of North America 2010; Giblin et al. [eds] 2018). Subularia aquatica was first documented in Montana from Lincoln County in 2022 during surveys conducted by Montana Fish, Wildlife & Parks through the Aquatic Invasive Species Program. The conservation status for Subularia aquatica in Montana has not yet been ranked (SNR). Information is needed to document this plant’s population size, distribution, and life history in Montana, along with any potential threats to its persistence.

NOTE: It is important to document new occurrences by providing quality pressed plant specimens to one of our State herbaria (University of Montana, Montana State University, or Montana State University-Billings). Herbarium specimens allow identifications to be confirmed, provide a central location for education and information sharing, are a source for genetic, morphological, and ecological studies, and are the basis on which Montana's floras are written.
General Description
PLANTS: An aquatic annual that grows up to about 10cm tall. Plants have mostly basal leaves and one or more erect, unbranched stems that terminate into an inflorescence. Plants lack hairs (glabrous). Sources: Al-Shehbaz in Flora of North America [FNA] 2010

LEAVES: Basal, forming a rosette of leaves, 1-7 (-10) cm long. Blades are sessile to the stem, erect to ascending, awl-shaped (subulate), almost roundish, and with entire margins. Cauline leaves are lacking. Sources: Al-Shehbaz in FNA 2010; Giblin et al. [eds] 2018

INFLORESCENCE: A congested raceme of (1) 2-12 (-18) flowers that may elongate in fruit. Pedicels typically form a 30 to 50 degree angle with the rachis, are stout, and 1-7 (-10) mm long. Sepals are persistent. White flowers may open to pollinate (chasmogamous) or remain closed to self-pollinate (cleistogamous). Fruits are oval to elliptical silicles. Sources: Al-Shehbaz in FNA 2010; Giblin et al. [eds] 2018

Flowering from July through October (Al-Shehbaz in FNA 2010).

Diagnostic Characteristics
In our region, Subularia aquatica is the only aquatic plant with silicles that belongs to the Mustard (Brassicaceae) Family. Plants have one or more unbranched, leafless flowering stems (peduncle) and basal leaves that are linear, roundish, and slightly curved (like an awl). Plants are easily over-looked due to their size and sparse populations.

The genus Subularia comes from the latin word of subula and refers to the leaf’s shape Al-Shehbaz in FNA 2010.

Plants in the greater Pacific Northwest belong to the subspecies americana G.A. Mulligan & Calder (Giblin et al. [eds] 2018).

Range Comments
i>Subularia aquatica occurs in most western and north-central states of the United States of America (USA) and most provinces of Canada (Al-Shehbaz in FNA 2010). In the greater Pacific Northwest plants occur from British Columbia, Canada to northern Washington and occasionally in Idaho (Giblin et al. [eds] 2018). Plants also occur in Yellowstone National Park, Wyoming (Lesica et al. 2022). The first documented occurrence of Subularia aquatica in Montana was found in 2022 from Lincoln County.

Observations in Montana Natural Heritage Program Database
Number of Observations: 2

(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)

Subularia aquatica grows in freshwater ponds and lakes where it is often submerged (Giblin et al. [eds.] 2018). Plants can also grow along shorelines and margins of muddy ponds, wet sedge meadows, shallow sandy water flats, rocky/gravelly streams, muddy tidal flats, salt marshes, gravelly lake beaches, and lakes (Al-Shehbaz in FNA 2010). Plants occur in sparse populations (Giblin et al. [eds] 2018).

In Montana, Subularia aquatica was found growing submerged in the silt bottom of a lake.

Reproductive Characteristics
Plants reproduce by seed.

FLOWERS Source: Al-Shehbaz in FNA 2010
Sepals are persistent, (0.5) 0.7 mm wide by 1.0 (-1.3) mm long. Petals are white, 1.2-1.5 mm wide by 0.2-0.5 mm long. Stamens are subequal with filaments, 0.7-1.0 mm long, and anthers, 0.1-0.2 mm long. The pistil lacks a style and is stalked (gynophore), 0.2-0.1 (-1) mm long.

FRUITS Source: Al-Shehbaz in FNA 2010
Fruits are silicles, (0.15-) 0.2-0.35 (-0.55) cm long by 1.2-2.0 (-2.5) mm wide. Seeds are light brown, 0.8-1.0 mm by 0.5-0.8 mm. Seeds are biseriate, slightly compressed, oblong, and not winged. Seed coat is not mucilaginous when wetted.

GENETICS Source: Al-Shehbaz in FNA 2010
Haploid chromosome numbers for Subularia chromosomes have been published as x = 14, 15. Diploid chromosome numbers for Subularia aquatica have been published as 2n = 30.

LIFE CYCLE Source: Al-Shehbaz in FNA 2010
Flowers may open to pollinate through sexual exchange (chasmogamous) or may remain closed and self-pollinate through cloning (Cleistogamous).

Threats or Limiting Factors
In Washington populations of Subularia aquatica have been lost when lakeshores are developed, docks are installed, and from increased levels of swimming and boating activities, particularly when aquatic plants are purposely removed from the lake's nice sandy bottoms (Zika personal communication).

  • Literature Cited AboveLegend:   View Online Publication
    • Al-Shehbaz, I.A. 2010. Brassicaceae. In: Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford. Vol. 7.
    • Hitchcock, C.L. and A. Cronquist. 2018. Flora of the Pacific Northwest: An Illustrated Manual. Second Edition. Giblin, D.E., B.S. Legler, P.F. Zika, and R.G. Olmstead (eds). Seattle, WA: University of Washington Press in Association with Burke Museum of Natural History and Culture. 882 p.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2022. Manual of Montana Vascular Plants, Second Edition. Fort Worth, TX: BRIT Press. viii + 779 p.
    • Zika, Peter. 2023. Electronic correspondence on observed threats to Subularia aquatica. University of Washington Herbarium, Seattle, Washington.
  • Additional ReferencesLegend:   View Online Publication
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    • Mulligan, G.A. and J.A. Calder. 1964. The genus Subularia (Cruciferae). Rhodora 66(766):127-135.
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Citation for data on this website:
Water Awlwort — Subularia aquatica.  Montana Field Guide.  .  Retrieved on , from