Isoetales

 
Isoetes  
The order Isoetales includes the modern "quillwort", the living genus, Isoetes with about 70 species, which has a worldwide distribution, and very similar fossils (Isoetites a mid-Cretaceous plant resembling modern Isoetes). These are small, often aquatic plants with a short stem and elongate leaves. These are highly reduced plants that have effectively "telescoped" the body into a small corm-like stem that lacks vegetative leaves (all the leaves are fertile sporophylls). Fossil forms are sometimes placed in the modern genus Isoetes. Like the more primitive Selaginellales, the Isoetales are heterosporous, producing two kinds of spore.

The Isoetales are the most advanced of the lycopsids, and many unusual features with the great Carboniferous scale trees (Lepidodendrales) including secondary tissue development (both wood and bark), a modified shoot system that acts as a rooting system, bipolar growth and an upright plant habit.   Despite the superficial difference in size and form, they could actually be considered miniaturized versions of the mighty scale trees. Although the scale trees died out with the drying of the climate during the latest Carboniferous, their tiny aquatic relatives the Isoetales survived as living fossils to the present day.

The Order Isoetales and Lepidodendrales are sometimes included in the Subclass Ligulatae - defined by the presence of ligules, heterospory, and endospory. There is also a tendency now to include the Chaloneria, Pleuromeia, and Nathorstiana under the order Isoetales, although Pleuromeia, is sometimes also considered a late and specialized Lepidodendrale. Because of the uncertainty of placing these transitional forms, I have retained the old order Pleuromeiales for them, at least for now

Order Isoetales
Isoetaceae (Isoetes, Stylites, Isoetites)

Links

The Isoetes Page, Laboratorio Fisiologia Vegetale e Micropropagazione, Universita degli Studi di Palermo, Italy - everything there is to know about Isoetes

Quillworts: a small page on Isoetales with some useful diagrams

The delayed resurgence of equatorial forests after the Permian ...: a scientific paper which discusses the ecological importance of Isoetales in the recovery from the end-Permian extinctions. This paper is discussed in more detail in connection with the Olenekian Age of the Early Triassic.