Marsilea sp., or Water Clover, is an interesting aquatic fern distributed world wide. There are 65 species within the genus Marsilea. The plants resemble the 4-leaved clover (Trifolium), except that 4 leaflets are the rule rather than the exception in Marsilea. The plants that we propagate grow leaves that are up to 6-8 inches (15-20 cm) tall with their 4 leaflets reaching about 1-1.5 inches (2.5-3.5 cm) across. The fern spreads by a thin hairy underground rhizome. In nature, the plants are native to shallow water where the leaves float on top of the water. They are great plants for shallow aquariums and will grow in moist containers out of water as long as they don't dry out.
Blooming: This genus reproduces by producing hardened sporocarps, which are very specialized reproductive structures. This is the closest that ferns get to producing seeds! Sporocarps actually appear a bit like seeds and are born on short petioles, but they are more properly compared to reduced and hardened fertile pinnae. The sporocarps are green at first, turning grayish brown and becoming very hard at maturity. Sporocarps contain female spores called megaspores and male spores called microspores. The genus Marsilea is among the most advanced of the ferns in being heterosporous (the only others are the floating aquatic ferns Azolla and Salvinia). It can complete its life cycle within 10-15 hours once the sporocarps open.
Culture: Marsilea plants need a moist to wet soil with partial to full shade. In the greenhouse, we use a soil mix consisting of equal parts of loam and sand with a small amount of peat moss added. The plants are kept in tanks with the containers submerged to about 6 inches (15 cm) deep. The fronds float on top of the water for an interesting effect. We keep the water temperature around 68°F (20°C) all year long.
Propagation: Marsilea plants are vegetatively propagated by division of the rhizomes and reproductively multiply by germination of the sporocarps. Sporocarp germination is very interesting. Cut away a small part of the sporocarp (to admit water) and place the sporocarp in a petri dish containing distilled water. If conditions are right, a gelatinous ring with sori (groups of male and female sporangia) will emerge in a few minutes. Several hours later, megaspores and micospores are released into the water. Fertilization occurs within 12-24 hours after being placed in water. After 72 hours, the young sporophytes can be placed on wet mud in containers to mature.
Marsilea was featured as Plant of the Week February 17-23, 2006.
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Cal's Plant of the Week was provided as a service by the University of Oklahoma Department of Microbiology & Plant Biology and specifically Cal Lemke, who used to be OU's botany greenhouse grower and an avid gardener at home as well. If the above links don't work, then try the overview site. You may also like to look at the thumbnail index. ©1998-2012 All rights reserved.