When I traveled to California, the last fern that I was expecting to find outdoors was Regnellidium diphyllum, a narrow endemic species from S Brazil, N Argentina, and Uruguay. But there it was, vigorously growing in a garden pond. Almost everything about this fern is unusual. Besides being aquatic, the sori are borne within hardened bean-like structures called “sporocarps”. Each sporocarp has two types of sporangia (megasporangia and microsporangia), a condition that is very rare among ferns (i.e., heterospory). Regnellidium is the only living species of Marsileaceae with two pinnae, thus the common name “two-leaved marsilea”. It is also the only nonflowering plant that produces latex, which is formed in unbranched laticiferous ducts in the cortex of the stem, petiole, and lamina (Gifford & Foster, 1989).
Classification & Common Names
- Class: Polypodiopsida
- Family: Marsileaceae
- Genus: Regnellidium Lindm.
- Species: Regnellidium diphyllum Lindm.
- Common name(s): Two-leaved marsilea
- Location: – Orinda – Contra Costa County – California – United States.
- Coordinates: 37.882778, -122.179722
- Elevation: 300 m
Great shots, Fernando!
Thanks, Tom! The plant helped a lot.