Proserpinaca pectinata
A feathery aquatic plant with comb-like leaves and small flowers.
Proserpinaca pectinata, called combleaf mermaidweed, comb-leaved mermaid-weed, or feathery mermaid-weed, is a flowering plant that lives in water or wet ground. It belongs to the Haloragaceae family and is native to eastern North America and Cuba.
French naturalist Jean-Baptiste Lamarck first described the species in 1792. The name *pectinata* comes from the Latin word for comb-shaped, referring to its leaf form. In 1910, Kenneth Kent Mackenzie described a plant from New Jersey’s Pine Barrens as *Proserpinaca intermedia*, based on leaves that looked intermediate between *P. palustris* and *P. pectinata*. Later treatments disagree on its status. Go Botany treats it as a rare hybrid (*Proserpinaca × intermedia*) known from Massachusetts and Rhode Island, with pinnately lobed submerged leaves, a broader central rachis than *P. pectinata*, and different fruit size. The Digital Atlas of the Virginia Flora excludes it from formal recognition there, noting that records have been interpreted as a hybrid, a species of hybrid origin, or environmentally induced plasticity, and that no solid evidence supports a hybrid origin.
This perennial herb has trailing or decumbent stems that may rise toward the tips, reaching up to 50 cm long. Leaves are alternate, simple, and deeply split into narrow, comb-like segments (not separate leaflets). Leaf blades are mostly 13–23 mm long, with final segments 2–7.5 mm long. Unlike many aquatic plants, both submerged and emergent leaves stay deeply pinnately divided and feathery. Flowers are small, radially symmetrical, and stalkless in the axils of emergent leaves. Each flower has an inferior ovary, three sepals, three stamens, and three carpels. The fruit is a small, dry, indehiscent, three-loculed nutlet or schizocarp, 2–2.8 mm long.
To tell *P. pectinata* from the more common *P. palustris*, look at the floral bracts: *P. pectinata* has pinnately lobed or divided bracts, shorter leaf blades, and lower leaves with mostly six to nine pairs of segments. *P. palustris* has toothed bracts, usually longer leaf blades, and lower leaves with seven to fourteen pairs of segments. Also, *P. pectinata* keeps similar pectinate leaves above and below water. It can resemble aquatic milfoils like *Myriophyllum aquaticum*, but mermaidweed has one leaf per node, while parrotfeather has leaves in whorls.
Quick Facts
- Genus
- Proserpinaca
- Species
- pectinata
Facts from the source article.
Lore & Background
Proserpinaca pectinata was first described by Jean-Baptiste Lamarck in 1792. Its specific epithet, pectinata, is derived from Latin pectinatus, meaning comb-shaped or pectinate. In 1910, Kenneth Kent Mackenzie described Proserpinaca intermedia from material collected in the New Jersey Pine Barrens, distinguishing it from P. palustris and P. pectinata by its intermediate leaf morphology. The status of P. intermedia has been interpreted differently by later floristic treatments; Go Botany treats it as Proserpinaca × intermedia, a rare hybrid of P. palustris and P. pectinata, while the Digital Atlas of the Virginia Flora excludes the taxon from formal recognition, noting that empirical evidence for hybrid origin is lacking.
The species is a perennial wetland herb with trailing to decumbent stems that may become ascending toward the tips, reaching up to 50 cm in length. Leaves are alternate, simple, and deeply divided into narrow, comb-like segments, with leaf blades mostly 13–23 mm long. Both submerged and emergent leaves are deeply pinnately divided and feather-like. Flowers are small, radially symmetrical, and borne without stalks in the axils of emergent leaves, with an inferior ovary, three sepals, three stamens, and three carpels. The fruit is a small, dry, indehiscent, three-loculed nutlet or schizocarp, 2–2.8 mm long.
Proserpinaca pectinata can be distinguished from the more common Proserpinaca palustris by its pinnately lobed or pinnately divided floral bracts, shorter leaf blades, and lower leaves with mostly six to nine pairs of segments. It may also resemble aquatic milfoils such as Myriophyllum aquaticum, but mermaidweed has one alternate leaf per node, while parrotfeather has leaves arranged in whorls.
Reader's Guide
Proserpinaca pectinata is significant as a distinctive aquatic plant of eastern North America and Cuba, with a unique leaf morphology that remains consistently pectinate in both submerged and emergent forms, unlike many aquatic plants. Its taxonomic history includes a disputed taxon, Proserpinaca intermedia, described in 1910 from the New Jersey Pine Barrens, which later treatments have variously interpreted as a hybrid or environmentally induced plasticity, with no empirical evidence for hybrid origin. The species is globally secure (NatureServe G5) but is rare or legally protected at the northern edge of its range, including Michigan (ranked S1 and listed as endangered) and New York (listed as a threatened native plant). Its conservation status highlights the vulnerability of disjunct populations, such as the single known occurrence in Michigan, first collected in Ottawa County in 1941, initially misidentified as P. palustris, and rediscovered in 1984. The species' association with sandy coastal-plains wetland habitats underscores its ecological niche in seasonally inundated freshwater wetlands, including pond margins, bogs, marshes, and ditches.
Did You Know?
- Its specific epithet, pectinata, means 'comb-shaped' in Latin.
- The species has both submerged and emergent leaves that are deeply pinnately divided and feather-like.
- In Michigan, it is known from a single sandy, wet, peaty ditch and is listed as endangered.
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