Member of the water starwort family. The plants are rooted in the vernal pool bottom and have long, stringy stems which end in a cluster of floating leaves. The flowers are tiny (up to 1 mm across) and are seldom seen. Flowers occur down where the leaf meets the stem.

Other species of Callitriche may occur at Mather Field in the wetlands and along drainage channels, but Callitriche marginata is the only species which occurs regularly in vernal pools.

Water Starwort is an annual. It germinates in wet areas soon after the rains begin in the fall. As the vernal pools fill, the stems get very long so that the leaves can float on the surface of the water. As the water evaporates, the floating leaves drift around because their stems are now longer than the distance between the water surface and the soil.

Water Starwort flowers shed pollen on the surface of the water where the wind and water's surface tension carry it to other Water Starwort flowers for cross-pollination.

As soon as the water evaporates, the Water Starwort plants its seeds in the drying mud. To do this the stems below the ovaries grow very quickly and push them into the soil. This guarantees that the next generation will have a suitably wet spot in which to grow.