Isoëtes

Isoëtes is a genus of perennial, root-sporing herbaceous plants in the division Lycophyta. Commonly known as quillworts, they are aquatic or semi-aquatic in habit, typically found in clear, cool, shallow waters or on moist soil. The plants are characterized by their unique morphology. They possess a corm-like, often lobed stem from which numerous long, grass-like leaves emerge. These leaves are typically dark green to black and can be quill-like, hence the common name.

Reproduction in Isoëtes involves spores. They are heterosporous, meaning they produce two types of spores: large megaspores and small microspores, housed within megasporangia and microsporangia, respectively. These sporangia are found at the base of the leaves. The life cycle involves a reduced gametophyte generation.

The distribution of Isoëtes is global, found on all continents except Antarctica. They occupy a variety of habitats, from freshwater lakes, streams, and ponds to ephemeral pools and seepages. Their presence is often an indicator of good water quality.

There are approximately 200 recognized species within the genus Isoëtes. Their phylogenetic position is of considerable interest to botanists, as they are considered to be among the most ancient lineages of vascular plants. Their unique characteristics and ancient lineage make them a subject of ongoing scientific study.