Rare Species Guide

  Synonyms

Sagittaria montevidensis ssp. calycina, Sagittaria calycina

  Basis for Listing

Sagittaria calycina var. calycina (hooded arrowhead) is known to occur in several south-central states. It is apparently not uncommon in the center of its range; however, it is rare or uncommon in the northern part of its range, including Minnesota and adjacent states. Perhaps the major reason native plant species become rare in Minnesota is loss of habitat. In some cases, the loss of habitat can become so acute it threatens the continued existence of the species within the state. This is certainly the case with S. calycina var. calycina. The habitat under consideration is wetlands, in all forms, including the littoral zone of small and large-size lakes and ponds, as well as shallow marshes, streams and rivers. All of these habitats can, to one extent or another, provide habitat for S. calycina var. calycina, and all have suffered severe losses as a result of human activities (Minnesota's Remaining Native Prairie). At this time, the species is known to occur at a comparatively few scattered sites in Minnesota  (Minnesota and Northeast Iowa Morainal, North Central Glaciated Plains, and the Paleozoic Plateau sections) that have escaped significant human habitat alteration. For these reasons, S. calycina var. calycina was listed as a threatened species in Minnesota in 2023.

  Description

Sagittaria calycina var. calycina is an annual; it lacks rhizomes and tubers. The emergent leaves are arrowhead-shaped, with one terminal lobe and 2 basal lobes. Due to the annual nature of the species, the leaves can vary in size from very small to 20 cm (8 in.) wide by 26 cm (10 in.) long. The basal lobes are about equal in size to the apical lobe; the apex of the leaf is acutely or obtusely pointed or infrequently rounded. The petioles are circular in cross-section, soft and spongy. The scape (stalk of the inflorescence) is initially ascending or spreading, ultimately reclining or recurving, 10-70 cm (4-28 in.) long, with 2-6 whorls of flowers; the pedicels (stalks of the individual flowers) are recurved, especially in fruit, 2-7 cm (0.8-2.8 in.) long, 1.5-10 mm (0.06-0.4 in.) thick. The flowers are unisexual, 2-5 cm (0.8-2 in.) across; the sepals are not reflexed. The achenes (seeds) are 2.2-2.8 mm (0.09-0.11 in.) long, in ± spherical heads, 1-2 cm (0.4-0.8 in.) across at maturity, and tightly enclosed by the sepals; the beak of the achene is 0.5-1.0 mm (0.02-0.04 in.) long, inserted laterally at the upper corner of achene, and is perpendicular to the axis of the achene; the tip of the beak is straight (Haynes and Hellquist 2000).

Field identification: There are six species of Sagittaria in Minnesota. They all have the word “arrowhead” in their common names even though they do not all have arrowhead-shaped leaves. They do all have white flowers, each with 3 petals and 3 sepals, and relatively large basal leaves that typically emerge from shallow water or wetlands.

Of the six species in Minnesota, S. calycina var. calycina  is the most distinctive, and perhaps the only one that can be reliably identified without mature seeds. In particular, notice the thick downward curving pedicels. The downward curving aspect is especially prominent after pollination. The other species of Sagittaria that occur in Minnesota have thin pedicels that grow straight outward or slightly upwards. Also, look at the sepals of the flower or fruit. When in flower, the sepals of S. calycina var. calycina are pressed tightly against the petals. When in fruit the sepals appear to tightly clasp the seed head. Sepals of other species curve away from the flowers and the seed head. It can sometimes be noticed that the leaves of S. calycina var. calycina are held somewhat horizontal to the ground, rather than vertical like the other species. This can be useful for field identification, but it is not always reliable. Shape and aspect of a leaf vary too much to be used for identification.

  Habitat

Habitats of S. calycina var. calycina are found in association with lake shores, river banks, ponds, and marshes in the southern third of the state. Most are in the prairie region of the state, but S. calycina var. calycina should not be considered a prairie species. It is found where water pH is non-acidic and fluctuates seasonally. Habitats that produce large exposed mud flats in May, June, or July are excellent habitat. Soft mud (silt), or loose and wet sand are suitable substrates. It does not grow well on firm substrates or in habitats dominated by perennial emergent species such as Typha angustifolia (narrow-leaved cattail) or some of the more aggressive Scirpus ssp. and Schoenoplectus ssp. (bulrushes) or Carex ssp. (emergent sedges). It typically inhabits the zone occupied by annual species. Suitable habitats can be short-lived or ephemeral in the sense they may not appear every year. They are largely dependent on rainfall patterns.

  Biology / Life History

Of the six species of Sagittaria in Minnesota, only S. calycina var. calycina is an annual; the other species are perennial. Being an annual, it reproduces only by seeds, which are produced by insect-pollinated flowers. Pollination can be performed by a large number of non-specialist insects, primarily bees. The fertile seeds float on the surface for some period of time and are dispersed on water currents and by waterfowl. The pedicels curve downward as the seeds mature and push the seed head into contact with the water or mud, sometimes burying the seeds. Seeds germinate throughout the growing season, if conditions are favorable (Kaul 1985). They can germinate in a saturated substrate, or when submerged in standing water to a depth of at least 50 cm (20 in.) Some seeds will germinate the summer following their production, others will remain dormant in the substrate for a period of at least 7 years (Kaul 1991). This indicates populations may maintain a viable seed bank in the substrate (Kaul 1985).

Because S. calycina var. calycina is an annual, all individuals of a population flower each year. There will be no non-flowering plants in the population, and nearly all flowers are fertile. Under favorable conditions, each individual plant produces flowers throughout the season, until the plant is killed by frost in the autumn. Even seeds germinating late in the season will produce flowers and seeds, though the output may be small. The result is an immense quantity of seeds. One report determined a single plant can produce 414,000 seeds per year (Kaul 1985).

  Conservation / Management

Healthy and full-functioning habitats of S. calycina var. calycina are typically inhabited by annual species of plants, rather than perennials. The unstable substrate, rapid siltation, in-stream erosion, ice-thrust events, and the extreme seasonal fluctuations in water levels are simply beyond the capacity of most perennial species to become established or to persist. However, S. calycina var. calycina thrives under such conditions. If these conditions are altered by dams, levies, diversions, ditches, or drain tiles (to name just a few examples), habitat conditions may change enough to favor perennial species, especially aggressive non-native species such as Typha angustifolia and Phalaris arundinacea (reed canary grass). Maintenance of an upland buffer of native vegetation adjacent to the high-water mark of the water body is also important.

  Best Time to Search

Sagittaria calycina var. calycina is distinctive enough to allow positive identification anytime during the growing season, depending on local conditions. However, in most years, the prime search period is early July through mid-October. The seeds (achenes) ripen from early August to mid-October, but are not necessary for identification of the species.

  Authors/Revisions

Welby Smith (MNDNR), 2018, 2026

(Note: all content ©MNDNR)

  References and Additional Information

Beal, E. O., J. W. Wooten, and R. B. Kaul. 1982. Review of the Sagittaria engelmanniana complex (Alismataceae) with environmental correlations. Systematic Botany 7(4):417-432.

Bogin, C. 1955. Revision of the genus Sagittaria (Alismataceae). Memoirs of the New York Botanical Garden 9:179-233.

Haynes, R. R., and C. B. Hellquist. 2000. Sagittaria. Pages 11-23 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 22. Oxford University Press, New York, New York.

Kaul, R. B. 1985. Reproductive phenology and biology in annual and perennial Allismataceae. Aquatic Botany 22(2):153-164.

Kaul, R. B. 1991. Foliar and reproductive responses of Sagittaria calycina and Sagittari brevirostra (Alismataceae) to varying natural conditions. Aquatic Botany 40(1):47-59.

Wooten, J. W. 1973. Taxonomy of seven species of Sagittaria from eastern North America. Brittonia 25(1):64-74