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Washington State Department of Ecology > Water & shorelines > Freshwater studies > Lake water quality > Aquatic Plant Guide home > Submersed Plants > Isoetes

Aquatic Plant Identification Manual for Washington's Freshwater Plants

Submersed Plants

Species: Isoetes spp., quillworts
Family: Isoetaceae

Several species of quillwort occur in the Pacific Northwest, all commonly found in seasonally wet to aquatic habitats. Each plant consists of a clump of 20-30 green to yellowish-green, grass-like, hollow leaves that taper to a pointed tip. Each clump arises from a bulb-like base. The leaves of the strictly aquatic underwater species are evergreen, while the wetland species have deciduous leaves. Quillworts reproduce by spores that are produced in the leaf bases. They are closely related to the primitive horsetail family (Equisetaceae). The most common quillwort in Washington lakes is western quillwort (Isoetes occidentalis).
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Leaf: The green, slender, hollow leaves each have a pointed tip and a spoon-like base. There are 10-30 leaves per plant and each leaf is divided length-wise into 4 chambers. The length varies from 3-24 cm and sometimes up to 70 cm. Spore cases are located in the swollen leaf-bases.

Stem: Quillworts have a modified stem called a corm. It is a corky-brown, bulb-like underground structure with 2 or 3 lobes, like a tiny onion. Roots grow from the lower surface and leaves from the upper surface.

Flower: None. 

Fruit: Quillworts produce spores instead of flowers or fruits. White megaspores about the size of salt grains are located in a sac within the outer swollen leaf bases. Microspores, the size of powder, are located in inner leaf bases. The spore sac is partly to completely covered by a thin flap (velum).

Root: Roots are unbranched or forked and grow in clusters from the base of the corm.

Propagation: Spores are dispersed by water or animals in the late summer.

Importance of plant: Deer feed on the leaves and muskrats and waterfowl eat the fleshy corms. Quillworts are intolerant of nutrient enrichment and can be an indicator of good water quality.

Distribution: Nearly worldwide. 

Habitat: Quillworts grow from shallow to moderate depths in lakes and slowly-flowing rivers on sandy substrates, mud, and wet ground.

May be confused with: Quillworts can be distinguished from spikerushes (Eleocharis spp.), sedges (Carex spp.), and flowering-quillwort (Lilaea scilloides) by the presence of spores and the swollen leaf bases. Quillwort species are distinguished from one another by microscopic examination of their spores, the spore sac, and velum. Quillwort species sometimes hybridize. 

Photographs: Isoetes sp. plants in water; closeup of several plants, closeup of single plant
Line Drawings: None available

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