Tiedemannia filiformis subsp. filiformis, commonly known as water cowbane, is a slender perennial wetland herb native to the coastal plains of the southeastern United States and the Bahamas. Instead of broad, divided foliage, it sends up smooth, rush-like stems and cylindrical, hollow structures that explain its Latin epithet filiformis, meaning thread-like.
Belonging to the family Apiaceae, this plant was originally described as Oenanthe filiformis by Thomas Walter in 1788 and spent decades classified as Oxypolis filiformis before molecular studies confirmed its placement in the genus Tiedemannia. As the autonymic subspecies, it represents the typical, hollow-quill form of the species rather than the northern inland lineage.
Rising from a cluster of tuberous, fascicled roots, the upright hollow stem reaches 50 to 150 centimeters in height. The subterranean tissues are anchored in waterlogged muck and peat, drawing oxygen downward from the aerial shoots.
True leaf blades are absent; in their place, the plant produces reduced leaves called phyllodes—hollow, cylindrical leaf stalks partitioned by internal cross-walls that look and act like rush stems. These quill-like structures are Divided by visible transverse septa (internal partitions) and taper toward the tip, minimizing water drag during seasonal flooding.
Blooms from summer through autumn, typically between July and October.
Living in cypress domes, wet pine savannas, and fluctuating coastal marshes requires a plant to survive both submerged roots and intense summer sun. Rather than investing in wide, fragile leaf blades that would tear in moving water or rot when submerged, Tiedemannia filiformis subsp. filiformis reduces its foliage to sleek, cylindrical tubes.
Taxon Synonyms: Tiedemannia bakeri, Conium filifolium, Oxypolis bakeri
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