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W. Carl Taylor & Jon E. Keeley

Perennial herb, aquatic to terrestrial. Stem: buried, corm-like, 2–3-lobed, corky, brown. Leaf: simple, in grass-like tufts, spirally arranged on stem top, erect to spreading, < 30 cm, linear above base. Sporangium: solitary, embedded in wide leaf base, < 1 cm, ± covered by a translucent membrane, male or female; male spores > 10000, < 0.045 mm, ± bean-shaped, gray or brown in mass; female spores 20–200, 0.2–0.7 mm, spheric, white, ± smooth, ridged, tubercled, or prickly.
1 genus, 200+ species: worldwide. [Taylor et al. 1993 FNANM 2:64–75] —Scientific Editors: Alan R. Smith, Thomas J. Rosatti.
Unabridged references: [Pfeiffer 1922 Ann Missouri Bot Gard 9:79–233]

(Greek: evergreen, from habit of some species) Perhaps most poorly known lycophyte genus. Mature female spores, found in decaying leaf bases or soil, critical for identification, as are hand lens for texture when dry, microscope with micrometer for size. Hybrids (spores of variable size, shape) common between aquatic species, making them less distinct.

Key to Isoetes

I. howellii Engelm.
Plant becoming terrestrial. Leaf: deciduous, < 30 cm, rigid, not brittle, tapered to tip, bright green; base ± brown to black. Sporangium: membrane covering < 75%; male spores 0.025–0.035 mm, brown in mass; female spores 0.3–0.5 mm, ridged.
2n=22. Vernal pools, lake margins; generally < 1500(2900) m. Klamath Ranges, North Coast Ranges, Cascade Range, Sierra Nevada Foothills, n High Sierra Nevada, Great Central Valley, Central Coast, San Francisco Bay Area, South Coast Ranges, South Coast, Peninsular Ranges; to Washington, Montana, Utah. Small plants of South Coast, Washington, Baja California (leaf < 10 cm, female spore < 0.42 mm) are assignable to Isoetes howellii var. minima (A.A. Eaton) N. Pfeiff., recognition of which remains questionable pending further research, although it is ± clear that it should not be treated as an infraspecific taxon of Isoetes howellii. Spores mature late spring, summer. [Online Interchange]

Previous taxon: Isoetes echinospora
Next taxon: Isoetes nuttallii


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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora,, accessed on Nov 26 2015
Citation for this treatment: [Author of taxon treatment] 2013. Isoetes, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on Nov 26 2015

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click for enlargement Isoetes howellii
See CalPhotos for additional images
© 2004 Carol W. Witham

Geographic subdivisions indicated for the distribution of Isoetes howellii 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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Data provided by the participants of the Consortium of California Herbaria.
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CCH collections by month

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