Jepson eFlora: Taxon page
Vascular Plants of California
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Ceratophyllum demersum

Higher Taxonomy
Family: CeratophyllaceaeView Description 
Habit: Perennial herb, submersed aquatic; overwintering on bottom as detached, dense shoot tips (winter buds); roots 0; monoecious; water-pollinated. Stem: flexible with water currents, internodes clustered near tip. Leaf: whorled, generally compound, forked; segments linear, toothed; stipules 0; petiole 1--2 mm, translucent. Inflorescence: reduced axillary cymes generally near shoot tips, +- sessile, 1--several per node, generally staminate below, pistillate above, or sometimes mixed at a node; flowers 1--3 per cyme but appearing to be 1 subtended by calyx-like whorl of 8--15 bracts, bracts linear, leaf-like, fused at base, toothed at tip, persistent in fruit. Flower: unisexual; perianth 0; staminate round-topped, stamens 3--50, spirally arranged, anthers +- sessile, exserted from bracts, pollen shed underwater; pistillate of 1 simple, ovoid pistil, ovary superior, chamber 1; placenta pendulous; style elongate, spine-like, with decurrent groove; stigma pocket-like, at style base; ovule 1. Fruit: achene, tubercled or not, spines 0 or elongate, basal, facial, marginal or stylar; lateral margin winged or not.
Genera In Family: 1 genus, 6 species: +- worldwide.
eFlora Treatment Author: Donald H. Les
Scientific Editor: Thomas J. Rosatti.
Genus: CeratophyllumView Description 

Common Name: HORNWORT

Etymology: (Greek: horn leaf, for antler-like appearance) Note: Ceratophyllum grown as ornamental or for oxygen generation in aquaria, garden ponds. Leaves, fruit eaten by migrating waterfowl. Vigorous growth (even of native species) can result in weedy infestations.
Ceratophyllum demersum L.
Stem: 1--3+ m, glabrous, limp, suspended by water, brittle, branches 0--3 per node. Leaf: 3--11 per node, 0.8--3 cm; segments 2--4, with 2 rows small teeth distally, 1 multicellular, glandular appendage at tip. Inflorescence: uncommon. Flower: staminate 2--5 mm, stamens pink to +- red; pistillate 1--2 mm, pistil generally +- yellow, margins red-tinged or not, style generally 1 mm. Fruit: 3.5--6 mm (except spines), dark green to red-brown, generally tubercled, base with 2 tubercles or 2 spines, margin spineless, wingless; spines 0.1--12 mm, stiff, bases generally webbed; style persistent on fruit, stiff, erect, 0.5--14 mm. Seed: cotyledons large, fleshy; terminal bud highly developed; first leaves simple, opposite, awl-like. Chromosomes: 2n=24,38,40,48.
Ecology: Common. Ditches, lakes, ponds, pools, slow watercourses; water 0.1--4 m deep, fresh to +- brackish, medium to high nutrient levels, acidic to alkaline (pH 5.9--9.4) but generally alkaline (pH > 7); Elevation: generally < 1700 m. Bioregional Distribution: CA (exc CaRF, Teh, ChI, W&I, DMtns); Distribution Outside California: common worldwide. Flowering Time: Jun--Aug Note: Plants self-fertile; populations generally > 50% staminate.
Synonyms: Ceratophyllum apiculatum Cham.
Unabridged Note: Plants with fruit having basal tubercles instead of spines were named Ceratophyllum apiculatum Cham., but such variants occur commonly and sporadically throughout sp. range and do not merit taxonomic recognition.
Jepson eFlora Author: Donald H. Les
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Botanical illustration including Ceratophyllum demersum

botanical illustration including Ceratophyllum demersum


Citation for this treatment: Donald H. Les 2012, Ceratophyllum demersum, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on October 20, 2019.

Citation for the whole project: Jepson Flora Project (eds.) 2019, Jepson eFlora,, accessed on October 20, 2019.

Ceratophyllum demersum
click for enlargement
© 2008 Neal Kramer
Ceratophyllum demersum
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© 2015 Barry Breckling
Ceratophyllum demersum
click for enlargement
© 2008 Neal Kramer

More photos of Ceratophyllum demersum in CalPhotos

Geographic subdivisions for Ceratophyllum demersum:
CA (exc CaRF, Teh, ChI, W&I, DMtns)
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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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All markers link to CCH specimen records. The original determination is shown in the popup window.
Blue markers indicate specimens that map to one of the expected Jepson geographic subdivisions (see left map). Purple markers indicate specimens collected from a garden, greenhouse, or other non-wild location.
Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.

CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa, if there are more than 1 infraspecific taxon in CA.
Blue line denotes eFlora flowering time.