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*The following is based on Gann, G.D., K.A. Bradley & S.W. Woodmansee. 2002. Rare Plants of South Florida: Their History, Conservation, and Restoration. The Institute for Regional Conservation: Miami. For updated species accounts, see Citation below. For the original text, follow the link in the Update field. If no Update field is displayed, then cite as the original publication.

Ceratophyllum muricatum Cham.
subsp. australe (Griseb.) Les
Prickly hornwort

South Florida Status: Historical. Last observed in 1978 on Big Pine Key.

Taxonomy: Dicotyledon; Ceratophyllaceae.

Habit: Perennial aquatic herb.

Distribution: Native to eastern North America and Mexico. Wunderlin (1998) reports it as rare in Florida in Brevard, Franklin, and Monroe counties.

South Florida Distribution: Monroe County Keys.

South Florida Habitats: Solution holes and ditches.

Protection Status: Not listed by any agency.

Aids to Identification: Fruits are important for proper identification, but this is the only species of Ceratophyllum reported for the Florida Keys. Its achene margins are winged, while those of C. demersum, which occurs on the South Florida mainland, has achenes with margins that are not winged.

References: Wood, 1959; Lowden, 1978; Flora of North America Editorial Committee, 1997; Wunderlin, 1998.

Synonyms: C. floridanum Fassett; C. submersum L., misapplied.

Historical Context: John Loomis Blodgett first collected prickly hornwort in South Florida between 1838 and 1853 (s.n., NY), probably on Big Pine Key, although the specimen label indicates only “South Florida.” Ellsworth P. Killip made the next collection in 1940 at Watson Hammock on Big Pine Key (32868, US), which is now located within National Key Deer Refuge. In 1953, Killip made a second collection at the same locality (43367, US), and a third collection from just north of Watson Hammock (40732, US). George N. Avery made two observations of prickly hornwort at Watson Hammock, in 1974 and 1978, in mosquito control ditches (Avery’s Notes, 28 April 1974 and 16 December 1978). During a survey he conducted in 1979, he was unable to find any plants (Avery’s Notes, 12 June 1979).

Comments: This species may be somewhat ephemeral. Les (in Flora of North America Editorial Committee, 1997) states that “the affinity of C. muricatum for shallow, ephemeral habitats results in its sporadic and nonpersistent occurrence.” Any surveys that are conducted for this species should be done for several seasons over a period of several years. The South Florida occurrence of this species has been described as C. floridanum Fassett. See Lowden (1978) and Les (in Flora of North America Editorial Committee, 1997) for discussions of the typification and taxonomy of this species. Wunderlin (1998) reports this as introduced in error.

Recommendations: · Survey Watson Hammock area in the National Key Deer Refuge. · If plants are found, map and monitor known populations. · If no plants are found, consider reintroduction to the Watson Hammock area in the National Key Deer Refuge. · Review for listing by FDACS and FNAI.