Pondweeds & Allies

Rafinesque's Pondweed Rafinesque's Pondweed Fennel-leaved Pondweed Rafinesque's Pondweed

What are they?

Pondweeds are mostly aquatic species, so it's necessary to get a little wet to study them! Some species grow in wet ground that more or less drys out in summer and tend to have broader leaves. Others are entirely submerged and generally have long, grass-like leaves.

Where are they found?

Most freshwater bodies hold at least one species of pondweed, and often more. Many of the thread-leaved species are subaquatic, making them much harder to find.


A difficult group to identify to species as the parts are very small and a hand lens is required. Details of the leaf and stipules are important for identification.

One technical term that it is useful to know when identifying this group is Stipule. Stipules are like wings that are borne in pairs at the base of the leaf stem (this stem is called the petiole). On many pondweeds, these stipules are long and thin and often form sheath around the stem.

Rafinesque's Pondweed      Potamogeton diversifolius

Common in wetlands throughout Cape May County, being found in both permanent and summer-dry sites. A very variable species. Flowers June to July.
Rafinesque's Pondweed Rafinesque's Pondweed Rafinesque's Pondweed Rafinesque's Pondweed
Typical floating leaves
Submerged leaves
Flower spike
Seed head

Leafy Pondweed      Potamogeton foliosus

Rare in South Jersey in fresh and slightly brackish water and first found in Cape May County in 2013. Flowers June to September. Best told by its very slender leaves and by its fruits, which have distinctly knobbly edges.
Leafy Pondweed Leafy Pondweed
Seed capsules

Curly Pondweed      Potamogeton crispus

An introduced species from Europe. First discovered in Cape May County in 2013 in South Cape May. Flowers July to August. The strap-like leaves with well-toothed margins are unlike any native species in the area.
Curly Pondweed Curly Pondweed Curly Pondweed Curly Pondweed
Leaf close-up

Fennel-leaved Pondweed      Stuckenia pectinata

Known to be common in ponds south of Cape May Canal. Flowers July to August.
Fennel-leaved Pondweed Fennel-leaved Pondweed Fennel-leaved Pondweed Fennel-leaved Pondweed
Flower buds
Open flowers

Wigeon-grass      Ruppia maritima

A common aquatic plant in coastal brackish waters. Flowers June to September. Wigeon-grass is in a family separate from the pondweeds but is extremely difficult to tell from some of them when not in flower. Perhaps the easiest way to recognize this plant is after it sets seeds, when the elongating stems of the seed heads become spirally twisted.
Wigeon-grass Wigeon-grass Wigeon-grass Wigeon-grass
Flower buds
Seed capsules
Spiral fruiting stalks

Rigid Hornwort      Ceratophyllum demersum

Though this plant is native to North America, it is commonly used as an aquatic plant in aquariums and garden ponds and recent records in Cape May County seem mst likely to be of introduced plants. Currently known from the lower half of the county in large ponds. Flowers July. Hornworts are included here with pondweeds as they all grow together as aquatic plants. However, hornworts are in their own family (the Ceratophyllaceae) and are most closely related to the buttercup family.
Rigid Hornwort Rigid Hornwort Rigid Hornwort
Leafy shoot
Leaf segments