Quillwort

Quillwort is the common name for plants in the genus Isoetes, a group of small, spore-bearing vascular plants in the family Isoetaceae. Isoetes is a lycophyte and one of the oldest lineages of land plants. There are about 150 described species, distributed worldwide with a strong presence in temperate and subtropical regions. They are typically aquatic or semi-aquatic, inhabiting freshwater ponds, marshes, lake margins, and slow-moving streams.

Quillworts grow from a short underground stem or corm. Above ground, they form a rosette of narrow, hollow, quill-shaped leaves that resemble green pencils. The leaf bases enclose a small underground rhizome and roots. Leaves are usually stiff and ribbed, and plants can form dense tufts near the water surface or on the damp substrate depending on habitat.

Reproduction in quillworts is heterosporous, producing two distinct types of spores in separate sporangia. The sporangia are borne in a sporocarp at the base of the leaves. Megaspores give rise to female gametophytes, and microspores give rise to male gametophytes. The spores bear elaters, structures that aid in dispersal. The life cycle is that of a sporophyte-dominant plant, with free-living gametophytes that require water for fertilization.

Ecology and conservation: quillworts are indicators of moist, stable freshwater habitats. They are sensitive to habitat disturbance and water chemistry changes, and several species are considered threatened or of concern in various regions. They are also used in paleobotanical studies due to their ancient lineage.