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Chapter 3. Emergent Plants

Emergent species grow in shallow water at the margins of lakes or streams. These species are rooted below the water surface, but the stems, leaves, and flowers are mostly above the surface. Emergent plants often form a continuous band at the edge of the water at depths to about 1 m; the width of the emergent zone depends on the slope of the lake bottom.

ARROW-ARUM, TUCKAHOE

PELTANDRA RAF.

Arum Family—Araceae

Arrow-arum, tuckahoe

Peltandra virginica (L.) Schott & Endl.

Native

Rooted, emergent perennial

Arrow-arum is one of several emergent aquatic plants with large, arrow-shaped leaves. The plants consist of a cluster of long-petioled leaves that grow from buried vertical rhizomes. The strongly veined leaf blades are 5–20 cm long. Separate male and female flowers are packed closely on a fleshy stalk (spadix) that is enclosed in a tightly rolled green spathe. After pollination the flower stalk bends downward, pulling the developing fruits under the water surface, where the spathe eventually rots away, releasing the pea-sized fruits. The height of mature plants is up to 1 m.

Other emergent aquatic plants of similar stature and leaf shape include pickerel-weed (Pontederia cordata) and duck-potato (Sagittaria latifolia). Neither has a flower and fruit structure at all like arrow-arum. In addition, pickerel-weed has more rounded, heart-shaped leaves, and those of arrowhead are much thinner in texture and more variable in shape than arrow-arum.

The range of arrow-arum extends from southern Maine to Florida and inland to Michigan, Missouri, eastern Kansas, and Texas. In Pennsylvania it is found in the eastern and western portions of the state. Arrow-arum typically grows in water to 0.3 m deep in swamps and along the shorelines of rivers, lakes, or ponds. Flowering occurs from late spring through summer.

Native Americans used grated roots of arrow-arum in milk as a tonic for babies. Leaves, seeds, and fruits were also used for food. The fruits of arrow-arum are also eaten by wildlife, including waterfowl.

Peltandra virginica—leaf ×1/4

Peltandra virginica—inflorescence ×1/4

Peltandra virginica

ARROWHEAD

SAGITTARIA L.

Water-plantain Family—Alismataceae

The arrowheads are named for the shape of the leaf blade of the more prominent members. However, leaf shape is highly variable and influenced by water depth. Most species are emergent perennials; however, several grow completely submersed, and one species (S. calycina) is an annual. Individual flowers are unisexual, but both male and female flowers are borne on the same plant, making the species monoecious. The inflorescence is typically a raceme with female flowers in several whorls, each containing 3 flowers, at the bottom and male flowers in additional whorls above. The flowers are insect-pollinated. The fruit is a cluster of achenes. Seven species of arrowhead, all native, are present in Pennsylvania. An eighth, S. filiformis, known only from a few early collections in southern Bucks County, is believed to be extirpated.

Key to the Species of Arrowhead

A. sepals closely appressed in fruit ..................................................... Sagittaria calycina

A. sepals spreading or recurved in fruit

B. leaf blades rarely, or never, sagittate

C. stamens 7–15; plants low-growing, stoloniferous, mat-forming; leaf tips rounded; found only in freshwater intertidal marshes along the Delaware River ...................................................................... Sagittaria subulata

C. stamens 12–many; plants not mat-forming; leaf tips pointed in the rosette stage; of more widespread occurrence

D. female flowers sessile ..................................................... Sagittaria rigida

D. female flowers with a distinct pedicel ...................... Sagittaria graminea

B. sagittate leaf blades usually present

E. beak of the achene spreading to nearly horizontal ........ Sagittaria latifolia

E. beak of the achene ascending

F. beak to 0.5 mm; achene without facial wings; petioles not ridged ....... ..................................................................... Sagittaria cuneata

F. beak 0.7–1.7 mm; achene with 1 wing on each face; petioles ridged.... .................................................................... Sagittaria australis

Appalachian arrowhead

Sagittaria australis (J.G. Smith) Small

Native

Rooted, emergent perennial

Appalachian arrowhead is as much as 1 m tall with broad sagittate leaf blades. In overall appearance Appalachian arrowhead is very similar to the common Sagittaria latifolia, from which it is most easily distinguished by the presence of 5 longitudinal wings on the petioles. Like S. latifolia it produces stolons and corms. The inflorescence bears 5–12 whorls of 2.5 cm-wide flowers; the achenes have a strongly recurved beak.

Sagittaria australis

Appalachian arrowhead grows from New York south to Mississippi and Louisiana. In Pennsylvania it is found in river backwaters, wet meadows, and wet woods in the southern half of the state. Flowering occurs from late July to early September.

Sagittaria australis ×1/4

Sagittaria australis—achene ×5

Long-lobed arrowhead

Sagittaria calycina Engelm. [synonym: Sagittaria montevidensis Chamisso & Schlechtendal spp. calycina (Engelm.) Bogin]

PNHP

Native

Rooted, emergent or submergent annual

In Pennsylvania long-lobed arrowhead is a rare plant of the freshwater tidal zone of the Delaware River and its tidal tributaries. Submersed plants have strap-shaped leaves with a blunt tip; under emergent conditions sagittate leaves with long, spongy petioles are produced. Inflorescences contain several whorls of flowers; sepals remain closely appressed to the fruiting head. Unlike subulate arrowhead, another freshwater tidal species, longlobed arrowhead is not turf forming, but rather occurs singly or in small groups of 2–3 plants. Flowering occurs July to early September.

Sagittaria calycina ×1/2

Along the east coast long-lobed arrowhead is limited to tidal mudflats in Delaware, Pennsylvania, and New York. It also has a large interior range in the Mississippi River basin, but the main range of this plant is in South America. It has apparently expanded its range northward since it was first collected near Wilmington, Delaware, in 1860.

Sagittaria calycina—leaf variation ×1/2

Slightly wider leaves and appressed sepals help to differentiate long-lobed arrowhead from S. subulata. Sagittaria rigida and S. graminea also occur in the tidal zone, but these species have pointed leaves in the rosette stage.

Sagittaria calycina

Northern arrowhead

Sagittaria cuneata Sheldon

PNHP

Native

Rooted, emergent or submergent perennial

The leaves of northern arrowhead are sometimes completely submersed, or they may extend above the water surface on long petioles. The leaf blades are sagittate when emersed, with a central lobe that is larger than the basal lobes. When submersed the blade is elliptical (lacking basal lobes) or long and ribbon-like. Floating leaves may also be produced in deep water. The plants form large, edible corms.

The flowering stalk contains 2–10 whorls of white flowers, the upper staminate and the lower pistillate; the petals are 7–10 mm long. Stamen number ranges from 5–25. The achenes have a short, erect beak.

Sagittaria cuneata

This species is rare in pond margins and swamps in northwestern Pennsylvania. It is also known from one site in northeastern Pennsylvania where it was likely planted in a restored wetland. The main range of northern arrowhead extends from Nova Scotia and Quebec to Alaska and south to New York, Ohio, Texas, and California.

The corms of northern arrowhead were harvested by Native Americans; they are also an important source of food for wildlife. The achenes are eaten by ducks.

Submersed plants with ribbon-like leaves can be confused with water-celery (Vallisneria americana) or some of the bur-reeds (Sparganium spp.), but the venation is different and the leaves are not as strictly parallel-sided. See additional discussion under water-celery.

Sagittaria cuneata—achene ×5

Sagittaria cuneata ×1/4

Grass-leaved arrowhead

Sagittaria graminea Michx.

Native

Rooted, emergent or submergent perennial

Grass-leaved arrowhead is a rhizomatous perennial; it grows as an emergent or completely submersed where it sometimes forms a coarse turf. Underwater, the leaves are stiff, linear, and tapered to an acute tip; length and width can be highly variable. Emergent leaves typically develop an elliptical blade; lobed leaves are rare. The flowering stem contains 2–12 whorls of flowers; both male and female flowers are borne on individual pedicels. Flowering occurs from June to early August.

Grass-leaved arrowhead has a range covering the eastern half of the United States and adjacent areas of southern Canada. In Pennsylvania it occurs in the eastern half of the state in shallow water of lakes, ponds, and streams and on tidal mudflats.

Stalked female flowers distinguish this species from sessile-fruited arrowhead. In the absence of an inflorescence it is impossible to differentiate grass-leaved arrowhead from the sterile rosettes of other species based on appearance alone.

Sagittaria graminea ×1/2

Sagittaria graminea—juvenile rosette ×1/2

Sagittaria graminea

Duck-potato, wapato

Sagittaria latifolia Willd.

Native

Rooted, emergent perennial

Duck-potato is one of the most common emergent plants of lake and pond margins, swamps, marshes, and stream edges throughout Pennsylvania. The leaves are arrow-shaped with 2 backward-pointing basal lobes; the width of the main part of the blade and the lobes varies from plant to plant, ranging from very narrow to broad. Both leaves and flowering stems of this native perennial, which are up to 0.6 m tall, arise directly from a large, starchy, edible corm; stolons may also be present.

The flowering stalks bear 2–15 whorls of 3 flowers each; the lower whorls contain female flowers; male flowers are borne above. The flowers are white and 0.5–2 cm across; flowering occurs from July to early September. Fruiting heads are round and globe-like to somewhat flattened, up to 2.5 cm across, and the tiny, 6 mm-long achenes have a beak extending at a 90-degree angle to the body of the fruit.

The total range of arrowhead extends from Newfoundland and New Brunswick west to British Columbia, and south to northern Florida, Alabama, Louisiana, Texas, California, and Mexico.

The starchy corms of arrowhead were an important food for many Native American tribes. Known as “wappatoo” or “katniss,” the corms were prepared by baking, roasting, or boiling; they were also stored for winter use. Ducks, geese, and muskrats also eat the corms and seeds of this plant.

Sagittaria latifolia—inflorescence ×1/2

Sagittaria latifolia—leaf variation ×1/2

Sagittaria latifolia

Sagittaria latifolia—achene ×5

Sessile-fruited arrowhead

Sagittaria rigida Pursh

Native

Rooted, emergent or submergent perennial

Sessile-fruited arrowhead is a stoloniferous perennial with emergent or submergent leaves; corms also are produced. Underwater leaves are stiff, flattened, about 1 cm wide, and narrowed to an acute tip. Emergent leaves are typically elliptical or sometimes even develop a sagittate blade. Flowering can occur on emergent plants or those that are submersed in water 1–2 m deep. The inflorescence is characterized by female flowers that are attached directly to the main axis (sessile). In addition, the flowering stems are typically bent at the lowermost whorl of flowers.

Sessile-fruited arrowhead grows from Prince Edward Island to Wisconsin and south to Virginia and Missouri. Disjunct populations are known in Washington and California. In Pennsylvania, it is a plant of lake and pond margins, mudflats, and stream edges at scattered locations throughout. Flowering occurs from late July to late August.

If inflorescences are present, sessile-fruited arrowhead can be distinguished from the very similar grass-leaved arrowhead by the sessile female flowers. The two species are almost impossible to differentiate based on sterile rosettes alone.

Sagittaria rigida—inflorescence ×1/2

Sagittaria rigida—leaf variation ×1/5

Sagittaria rigida ×1/4

Sagittaria rigida

Subulate arrowhead

Sagittaria subulata (L.) L. Buch

PNHP

Native

Rooted, emergent or submergent perennial

This perennial species spreads by stolons to form a turf in the freshwater intertidal zone along the Delaware River and some of its tributaries. The plants are completely exposed at low tide and inundated at high tide. The 2.5–5 cm-long leaves are linear, sometimes with just a suggestion of an expanded blade at the tip. Flowering stems are slightly taller than the leaves and bear 2–3 whorls of flowers. Sepals of the fruiting heads are spreading or recurved. Flowering occurs from June to early September.

Subulate arrowhead has a limited global range in coastal areas of North America from Massachusetts to Mississippi. It is classified as a rare species in Pennsylvania.

Subulate arrowhead often occurs with long-lobed arrowhead, another species of freshwater tidal flats. See discussion above under Sagittaria calycina on how to distinguish these two species.

Sagittaria subulata ×2/3

Sagittaria subulata

BEGGAR-TICKS/BUR-MARIGOLD

BIDENS L.

Aster Family—Asteraceae

Bidens species are herbaceous annuals with opposite leaves and small flowers clustered in heads surrounded by an involucre which consists of large, leafy outer bracts and smaller membranous inner bracts. Additional (receptacular) bracts are associated with each individual floret.

Of the species treated here, only Bidens laevis produces ray flowers; all, however, are insect-pollinated. The fruits are achenes with 2–4 awns. These species are plants of shallow water of stream or lake margins or freshwater tidal marshes. The seeds are eaten by waterfowl.

Note: Bidens frondosa and Bidens cernua are included in the key due to their similarity to Bidens discoidea and Bidens laevis respectively. These species are not described below as they do not fit the criteria for aquatic plants treated in this work, despite the fact that they may occasionally occur in marginal habitat areas.

Key to Aquatic Species of Beggar-ticks and Bur-marigold

A. leaves compound

B. outer involucral bracts 3–5, not ciliate ............................................. Bidens discoidea

B. outer involucral bracts 5–10, ciliate ............................................. Bidens frondosa

A. leaves simple

C. leaves sessile; showy ray florets present

D. rays 1.5–3 cm long, receptacular bracts red-tinged ...................... Bidens laevis

D. rays less than 1.5 cm long, receptacular bracts yellowish .... Bidens cernua

C. leaves with distinct petioles; ray florets not present ................. Bidens bidentoides

Swamp Beggar-ticks

Bidens bidentoides (Nutt.) Britton

PNHP

Native

Rooted, emergent annual

Swamp beggar-ticks is a plant of freshwater tidal marshes. It has opposite leaves that are simple and coarsely toothed; the heads contain only disk flowers. A characteristic that distinguishes it from all the other Bidens species in our range is the upward pointing barbs on the awns of the achenes (visible with a 10X lens).

Swamp beggar-ticks typically grows in the upper zone of the tidal marsh where its roots are inundated at high tide but the upper stem remains above water. Its range includes freshwater tidal marshes of the estuaries of coastal rivers in New York, New Jersey, Pennsylvania, Delaware, and Maryland.

Bidens bidentoides—achene ×2, note upward-pointing barbs on awns

Bidens bidentoides ×1/3

Bidens bidentoides

Small beggar-ticks

Bidens discoidea (Torr. & A.Gray) Britton

PNHP

Native

Rooted, emergent annual

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