''Pilularia americana'', the American pillwort, is an unusual species of fern. The fronds essentially consist of the petioles only, any form of flattened laminae having been lost. It is in the aquatic fern family

Marsileaceae Marsileaceae () is a small family of heterosporous aquatic and semi-aquatic ferns, though at first sight they do not physically resemble other ferns. The group is commonly known as the "pepperwort family" or as the "water-clover family" because ...

, and is related to the water clovers and also to ''

Azolla ''Azolla'' (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more rese ...

'' and ''

Salvinia ''Salvinia'', a genus in the family Salviniaceae, is a floating fern named in honor of Anton Maria Salvini, a 17th-century Italian scientist. Watermoss is a common name for ''Salvinia''. The genus was published in 1754 by Jean-François Ségui ...

''.

Description

The pillwort, along with all other aquatic ferns in the order

Salviniales The order Salviniales (formerly known as the Hydropteridales and including the former Marsileales) is an order of ferns in the class Polypodiopsida. Description Salviniales are all aquatic and differ from all other ferns in being heterosporous, ...

, exhibits

heterospory Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore, is male and the larger megaspore is female. Heterospory evolved during the Devonian period from isos ...

and forms hard, seed-like sporocarps, as do the other members of the order. The sporocarps are distinctly different from the closely related genus ''Marsilea'' because they are globose in ''Pilularia'', while they are flattened in ''Marsilea''. The ferns in the genus ''Pilularia'' also have lost their leaf blades, with only the grass-like stipe remaining. However, this plant retains the

circinate vernation Vernation (from ''vernal'' meaning ''spring'', since that is when leaves spring forth in temperate regions) is the formation of new leaves or fronds. In plant anatomy, it is the arrangement of leaves in a bud. In pine species, new leaves are sho ...

characteristic of most ferns.

Distribution

The range of the American pillwort is well-established throughout much of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

and south-central

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idaho. T ...

. However, mostly only local occurrences have been found elsewhere in eastern North America. It is uncertain whether this reflects a genuinely sporadic occurrence, or whether this is a reflection of the fact that this is a small, grasslike, extremely easily overlooked plant. Close examination is often necessary to ascertain that this is a ''Pilularia''. The species also occurs through Central and South America, although scientific investigation may confirm those plants to be a separate species, ''P. mandoni'' A. Braun. Recent research has determined that the North American plants normally assigned to ''P. americana'' are actually two different (cryptic) species. The plants in most of the United States range are true ''americana'', while plants in southernmost California and Mexico are different, and are in fact very close genetically to the Australian and New Zealand species, ''

Pilularia novae-hollandiae ''Pilularia'' or pillworts is a genus of unusual ferns of family Marsileaceae distributed in North Temperate regions, Ethiopian mountains, and the southern hemisphere in Australia, New Zealand, and western South America. Depending on the taxono ...

'', and may possibly be eventually regarded as part of that species. pilularia americana-rangemap

Cultivation

This plant is easily grown given a suitable habitat and kept uncrowded. The pillwort also may die out for drier or colder parts of the season, regenerating the next year from the sporocarps. While it is in the aquatic fern group, it prefers to be emergent (in shallow water, with fronds emerging into the air) or growing completely emersed (fronds completely out of water), though preferring to be rooted in wet mud.

References

* Lellinger, David B. ''A Field Manual of the Ferns & Fern-Allies of the United States & Canada.'' Smithsonian Institution, Washington, D.C. 1985. *Nagalingum, Nathalie S., Michael D. Nowak and Kathleen M. Pryer. "Assessing phylogenetic relationships in extant heterosporous ferns (Salviniales), with a focus on Pilularia and Salvinia." ''

Botanical Journal of the Linnean Society The ''Botanical Journal of the Linnean Society'' is a scientific journal publishing original papers relating to the taxonomy of all plant groups and fungi, including anatomy, biosystematics, cytology, ecology, ethnobotany, electron microscopy, ...

'', 157(4): 673–685. 2008.

External links

Jepson Manual TreatmentUSDA Plants ProfileFlora of North AmericaPhoto gallery
{{Taxonbar, from=Q7194540 Salviniales Ferns of California Ferns of the United States Flora of Oregon Flora of the West Coast of the United States Garden plants of North America Freshwater plants Flora without expected TNC conservation status