The Marsileaceae, or water clovers, are a family of small, semi-aquatic ferns that resemble clover plants. They are part of the Salviniales, a group of ferns adapted to watery environments, and are notable for being one of the only four living plant groups that produce two types of spores: tiny microspores (male) and larger megaspores (female), a condition known as heterospory. Unlike their free-floating relatives, Marsileaceae are rooted to the substrate. Their long, slender stems connect anchored roots to delicate floating leaves that rest at the water’s surface. Fossils of this group are fairly common in Cretaceous rocks worldwide, including both four-lobed forms like modern Marsilea, two-lobed types like Regnellidium, and extinct forms grouped under the fossil genus Marsileaceaephyllum. Today, Marsilea species grow in muddy, slow-moving waters across tropical and subtropical regions. Their Cretaceous relatives seem to have preferred similar habitats, but their fossils have been found across a much wider range, from Canada all the way to Antarctica, suggesting they once thrived in warmer climates at higher latitudes.