Pontederia cordata
An emergent aquatic plant with tristylous flowers and edible seeds.
Pontederia cordata, called pickerelweed in the US and pickerel weed in the UK, is a monocot aquatic plant native to the Americas. It lives as an emergent plant in wetlands, such as the edges of ponds and lakes, across a vast range from eastern Canada down to Argentina. The plant relies on aerenchyma in its stem to move oxygen to its roots, though it can also tolerate low soil oxygen. It typically grows where water levels shift naturally, with spring floods and summer exposure. Soil fertility also matters, with the plant favoring more fertile bays in large lakes. Salinity, grazing, and competition from other wetland plants all harm it. Like many wetland species, it can survive tough times as buried seeds. A 36-year study in a sinkhole pond showed it has an inverse relationship with American lotus (Nelumbo lutea)—it declines when lotus is abundant and rebounds when lotus is scarce.
The plant flowers in late summer, producing slate blue blooms with yellow markings that likely attract bees. Two known pollinators are *Melissodes apicatus* and *Dufourea novaeangliae*. After flowering, the stem bends to submerge the fruits and seeds. The seeds are dormant when released and need 6–8 weeks of stratification to germinate. The flowers are tristylous, with three different style morphs usually all present in a population. Leaf shape varies widely across and within populations, even on the same plant, leading to many taxonomic synonyms. The species can also spread asexually through branching rhizomes, forming large clonal stands. The small seed pods are green and warty, dropping into the water when ripe.
This plant is grown as an ornamental in garden ponds and has earned the Royal Horticultural Society's Award of Garden Merit. Young leafstalks can be eaten raw or cooked, with unripe fruits removed. The seeds are edible raw and can be ground into grain.
Quick Facts
- Genus
- Pontederia
- Species
- cordata
Facts from the source article.
Lore & Background
Pontederia cordata is an emergent plant dependent on aerenchyma in the stem to carry oxygen into the roots, though its metabolism is also tolerant of low soil oxygen. It is often found in areas where water levels fluctuate naturally, such as spring flooding and later summer emergence, and tends to grow in more fertile bays of large lakes. The species is negatively affected by salinity, grazing, and competition from other wetland plants, but can survive unfavorable conditions as buried seeds in the soil. In a 36-year study in a sinkhole pond, it showed an inverse relationship with American Lotus (Nelumbo lutea), declining in years with high lotus abundance and increasing when lotus was low.
The plant flowers in late summer, with slate blue flowers bearing yellow markings that may assist in attracting bees for pollination; two known pollinators are Melissodes apicatus and Dufourea novaeangliae. The flowers are tristylous, meaning individual plants have one of three style morphs, and most populations contain all three. After flowering, the stem supporting the inflorescence bends to submerge the fruits and seeds. Seeds are dormant at dispersal and require 6–8 weeks of stratification to germinate. Leaf shape varies considerably across and within populations and even individuals, leading to many taxonomic synonyms. The species can also reproduce asexually via branching rhizomes, forming large clonal stands. The small seed pods are green and warty, released into the water when ripe.
Reader's Guide
Pontederia cordata is significant as a widespread native aquatic plant across the Americas, from eastern Canada to Argentina, inhabiting diverse wetlands such as pond and lake margins, northern rivers, the Everglades, and Louisiana. Its ecological role is shaped by its tolerance of fluctuating water levels and low soil oxygen, as well as its sensitivity to salinity, grazing, and competition. The 36-year study documenting its inverse relationship with American Lotus highlights its dynamic interactions within wetland communities. Its tristylous flowers and reliance on specific bee pollinators (Melissodes apicatus and Dufourea novaeangliae) illustrate a specialized reproductive strategy, while its ability to reproduce asexually via rhizomes allows it to form large clonal stands. The plant's seeds require stratification for germination, and its variable leaf shape has generated many taxonomic synonyms. Beyond its natural history, it is cultivated as an ornamental garden pond plant, earning the Royal Horticultural Society's Award of Garden Merit. Additionally, it has human uses: young leafstalks can be eaten raw or cooked, and the seeds are edible raw or ground into grain.
Did You Know?
- The flowers of Pontederia cordata are tristylous, with three different style morphs present in most populations.
- Its seeds require 6–8 weeks of stratification before they will germinate.
- In a 36-year study, the species showed an inverse relationship with American Lotus (Nelumbo lutea).
More in Aquarium and Aquatic Plants, Part 2 1-24
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