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Alan R. Smith & Andy Murdock

Plant free-floating or stranded on mud, generally 1–5 cm, often fan-shaped; roots pendent from stem forks, unbranched. Stem: forked repeatedly or pinnate, thread-like, easily fragmented at joints. Leaf: alternate, in 2 rows, sessile, often overlapped, 0.5–1.5 mm, seemingly paired but actually of 2 ± round to ovate lobes; upper lobe floating or emergent, thick, ± green or ± red, margin ± white, adaxial surface smooth or generally with papillae; lower lobe submersed, generally ± larger, thinner, ± white. Sporangia: in seemingly axillary cases of 2 kinds, cases generally in pairs of 1 kind. Male sporangium case: 1.2–2 mm diam, spheric; tip dark-pointed; wall transparent; sporangia generally 20–100+, long-stalked; spores 32 or 64, spheric, in generally 3–6 barbed masses. Female sporangium case: 0.2–0.4 mm diam, hemispheric or spheric; tip obtuse, covered by dark, conic, spongy structures that aid in flotation; wall ± opaque; sporangium 1, sessile; spore 1, spheric.
1 genus, ± 6 species: ± worldwide. When Salvinia and Azolla in same family, the name is Salviniaceae. —Scientific Editor: Thomas J. Rosatti.
Unabridged note: Barbs evidently on neither sporangia nor spores, but on cells surrounding spore masses. If Salvinia is included in the same family with Azolla, as is sometimes done, the name for the inclusive family would be Salviniaceae.

(Greek: dry kill, from plant death in dried habitats) [Reid et al. 2006 Int J Plant Sci 167:529–538] Used as green manure in rice paddies because of nitrogen-fixing algae in upper leaf lobe; species identification difficult, depends in part on fertile material (generally 0 on herbarium specimens). Species hybridize in culture.
Unabridged references: [Perkins et al. 1985 Scanning Electron Microscopy 1985(IV):1719–1734; Evard & Van Hove 2004 Syst. Geogr. Plant. 74:301–318]
Unabridged note: Evard & Van Hove (2004) treated Azolla microphylla as a synonym of Azolla filiculoides, suggesting that plants here called Azolla microphylla might instead belong to Azolla cristata Kaulf., although no California material was referred to this sp. by them.

Key to Azolla

A. microphylla Kaulf. MEXICAN MOSQUITO FERN
Plant green or blue-green to dark red. Stem: prostrate, generally 1–1.3 cm; internodes < 1 mm. Leaf: with generally conspicuous papillae on upper leaf lobe. Sporangium cases: male and female, often 0, female with equatorial girdle, wall ± smooth to pitted.
Ponds, slow streams; < 1200 m. n&s High Sierra Nevada, Great Central Valley, Central Coast, San Francisco Bay Area, San Bernardino Mountains, East of Sierra Nevada; to British Columbia, central United States, South America. [Azolla mexicana C. Presl] Geog ± uncertain due to confusion with Azolla filiculoides. [Online Interchange] {CNPS list}

Previous taxon: Azolla filiculoides
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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora,, accessed on Dec 1 2015
Citation for this treatment: [Author of taxon treatment] 2013. Azolla, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on Dec 1 2015

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Geographic subdivisions indicated for the distribution of Azolla microphylla Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).

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Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.