Floating Mat Rooted Plants  

Species: Hydrocotyle ranunculoides L. F., water pennywort
Family: Apiaceae

The most visible feature of water pennywort is the dark green, deeply-lobed, round leaves rising above the water surface. The plants are smooth and somewhat fleshy, with long creeping stems that often float near the waters surface. The small clusters of flowers occur on stalks attached to the horizontal stems. Often when the seeds ripen, the flower stalk bends toward the water surface. Water pennywort can form a dense mat of leaves along the edges of lakes and ponds and often remains green in winter. Look for this plant in western Washington.

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Leaf: The leaves are 2-6 cm in diameter, rounded or wider than long, with 3-7 lobes. The lobe divisions extend to about mid-leaf. The leaf edges are smooth to minutely scalloped. Long (5-35 cm) slender to stout stalks are attached to the leaf edge, although the stalk may appear to be attached to the center of the leaf.

Stem: Stems float on the water surface or sometimes creep onto shorelines. There are long spaces between leaf stalks.

Flower: Small white, greenish, or yellow flowers arise from the leaf base in clusters of 5-10 at the ends of 1-5 cm long flower stalks. Individual flowers are on short stalks within the clusters. Each flower has 5 tiny petals.

Fruit: The fruit is 1-3 mm long, elliptic to round, and flattened with faint ribs. It is divided into 2 halves, each with a tiny persistent stalk.

Root: Many fibrous roots emerge from the stems at the nodes. They hang free in the water column or root in the substrate.

Propagation: Seeds and creeping stems. 

Importance of plant: Water pennywort is included on Washington’s and British Columbia’s rare plant monitor list. It provides habitat for aquatic invertebrates and is occasionally used as an ornamental plant. In Australia, where it is not native, water pennywort can become a nusiance.

Distribution: North and South America. Found west of the Cascades in Washington. Introduced in Australia.

Habitat: Marshes, ponds, lake margins, and other wet ground.

May be confused with: Species of buttercup (Ranunculus spp.) which have flowers borne signly on flower stalks rather than in clusters and usually finely divided underwater leaves. Pepperwort (Marsilea vestita) which has four-parted clover-like leaves.  

Photographs: Hydrocotyle ranunculoides plants, closeup of leaf and stems

Line Drawings: Hydrocotyle ranunculoides

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