Aquatic Plants of Pennsylvania. Timothy A. Block
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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
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